Information

Are there animals that have evolved a resistance to human activity or encroachment?


There are countless sources, both peer-reviewed and popular, explaining how overuse and misuse of antibiotics is breeding a new generation of antibiotic-resistant "superbugs" such as MRSA (Methicillin-resistant Staphylococcus aureus) and MDR-TB (multidrug-resistant Tuberculosis). Over in the animal kingdom, the opposite seems to be happening - species after species is becoming endangered and/or extinct as humans destroy or alter their habitat through increased hunting, farming, construction, etc.

Are there any non-human animals that have been found to have evolved resistance to human encroachment into or alteration of their habitat in a way analogous to how bacteria have evolved resistance to human attempts to get rid of them? For example, this could consist of:

  • an animal that has adapted stronger bones to better survive collisions with vehicles
  • an animal that has significantly increased its blood coagulation rate to survive gunshot wounds from hunters
  • an animal that has developed better vision to see in urban environments
  • an animal that has evolved a skin pigment change that enables them to not take as much damage when they are sprayed with agricultural pesticides

One answer that came to mind is domestic animals - the horse and dog in prehistory, the cat in ancient Egypt, etc. That seems too obvious on one hand, and on the other hand may not really be an answer, as there seems to be no indication that pre-domestic animals were endangered by humans in any meaningful way. Are there animals that have significantly adapted themselves to surviving as wild animals in human-influenced environments?


Note: This is an answer to the last line of your question.

A classical example of animals adapting to the influence of humans on their environment is the adaption of the Peppered Moth.

Here is a brief summary:

The peppered moth was originally a mostly unpigmented animal (<1800). During the industrial revolution in the southern parts of the UK a lot of coal was burned. This led to soot blackening the countryside. Soon afterwards, a fully pigmented variety was first observed. Only a hundred years later, in 1895, this pigmented variety almost completely displaced the unpigmented variety.

It has been shown that the pigmentation is under strong selective pressure as birds hunt these moths. Since birds rely on their visual system to detect their prey, the variety that blends in with its environment (=camouflage) has a selective advantage over the variety that stands out.

As pointed out by Tim in the comments, since the 1970s there has been a rapid reversal with unpigmented animals being more abundant. As far as I understand, it is accepted that this reversal is due to a decrease in human induced air pollution leading to less sooty barks on trees which makes the unpigmented variety harder to prey upon.

Addendum: genetic basis of adaption

In a beautiful recent study, the causal mutation for the pigmented, or melanic, variety was identified: A ~9kb transposon insertion in the first intron of the gene cortex. The authors calculate that this mutation happened in the year 1819, a few years after the industrial revolution was in full swing. The interpretation is that due to sooty tree bark this mutation, causing pigmented moth, was under strong selection.


Many insects (as well as some other animals) have documented resistance to pesticides.

For example, the German cockroach (Blattella germanica) can be resistant to multiple insecticides1. In addition, some populations of this cockroach are now repelled by glucose, which leads to them avoiding traps2.

References:

1: Fardisi, M., Gondhalekar, A. D., Ashbrook, A. R., & Scharf, M. E. (2019). Rapid evolutionary responses to insecticide resistance management interventions by the German cockroach (Blattella germanica L.). Scientific reports, 9(1), 8292.

2: Wada-Katsumata, A., Silverman, J., & Schal, C. (2013). Changes in taste neurons support the emergence of an adaptive behavior in cockroaches. Science, 340(6135), 972-975.


Bighorn sheep are developing smaller horns and elephants are becoming tuskless in Africa:

The horns of some bighorn sheep are getting smaller, because hunters are picking off the most impressive rams before they reach their breeding peak

Elephant poaching, for example, is thought to have led to an increase in the number of tuskless animals in Africa.

Source


Nightingales have adapted to city noises by singing louder. Given that one function of singing is finding a mate there must indeed be a high, direct selection pressure to make oneself heard. Other birds have adapted in a similar fashion, e.g. by singing in a higher pitch, or at different times.


Not so much physical changes, but changes in behavior caused by human activity has numerous examples.
Foxes, pigeons, sea-gulls adapt very well to city life. Some species nowadays have larger numbers in cities than in the country side.
Polar bears are another good example. Disappearing sea-ice and increased human activity in the Artic has turned many polar bears into pre-dominantly garbage scavengers in stead of hunters/carrion-eaters.


The Impact of Human Activities on Biological Evolution: A Topic of Consideration for Evolution Educators

There is a definitive need, at all science education levels, to strongly emphasize the central anthropogenic role humans now play in current evolutionary processes and biosphere impact. This article presents a brief overview of recent human activities broad examples of the impact of human activities on biological evolution a general overview and specific examples of incorporating human activities into evolution education and further online anthropogenic resources that can be incorporated into educational settings.


2. Disease resistance

Evolution is about the survival of the fittest — and a big part of evolutionary fitness is not dying from a disease before you've had children. So it makes sense that evolution would be giving us a boost against some common diseases.

The most-studied disease we've been outrunning lately is malaria. If you've taken an introductory biology course lately, you may remember a strange connection with sickle-cell anemia. That's because there's a specific gene that, if you have one copy, will protect your red blood cells from invasion by the malaria parasite — but two copies will distort red blood cells and block their passage through blood vessels.

But that isn't the only trick that's evolved in the face of malaria. There are also more than a hundred slightly different genes that cause a shortage of a protein involved in breaking down red blood cells. That makes it harder for the malaria parasite to sneak into a red blood cell. Another type of mutation that's been spreading lately blocks malaria parasites from hanging out in the placenta.

And it's not just malaria — evolution has helped spread adaptations that protect against leprosy, tuberculosis, and cholera in certain populations as well. Some scientists have suggested that living in cities helps this process along.


The Principle of Societal Trust

As we consider the framework of policy solutions to combat antibiotic resistance, there is a fundamental principle that must be at the heart of our efforts. Antibiotics are unique among all drugs, and virtually unique among all technologies, in that they suffer from transmissible loss of efficacy over time (Spellberg, 2011 Spellberg et al., 2013 Spellberg et al., 2016). Because antibiotic-resistant bacteria spread from person to person, every individual’s use of antibiotics affects the ability of every other person to use the same antibiotics. Your use of an antibiotic affects our ability to use them. Our use affects your grandchildren’s future ability to use them. Antibiotics are therefore a shared societal trust or property. It is not acceptable for one group of people to abuse this trust for the purpose of perceived economic advantage, while harming everyone else.

In Western civilization, the rights of the individual have been paramount since the Magna Carta and the establishment of common law principles. Once an individual’s actions negatively affect others, however, limits are placed on those freedoms. For example, in the United States we recognize the rights of adults to consume alcohol, even up to the point of drinking themselves to death. Nevertheless, no person has the right to drink alcohol while driving a car, flying a plane, or doing surgery. The former affects only the individual. The latter affects others in society. The principle behind antibiotic usage is the same. We have the right to use them to benefit patients, but not to abuse them for perceived financial advantage (which may well be a false perception anyway, as discussed further below), in the process harming others.

Alexander Fleming, the discoverer of penicillin, warned the public about abuse of antibiotics in a 1945 New York Times interview. He said, “The microbes are educated to resist penicillin and a host of penicillin-fast organisms is bred out. . . . In such cases the thoughtless person playing with penicillin is morally responsible for the death of the man who finally succumbs to infection with the penicillin-resistant organism. I hope this evil can be averted” (Penicillin’s finder assays its future, 1945). Thus, 71 years ago, the man who brought penicillin to civilization also brought into specific relief the moral consequences of abusing this precious, societal trust.


Climate change could affect human evolution. Here's how.

As climate change brings rising temperatures, droughts, shifting patterns of precipitation and longer growing seasons, plants and animals are evolving to keep pace.

Biologists have observed squirrels and salmon developing at an accelerated pace, causing them to reproduce at a younger age. Earlier summers have caused some flowers to bloom earlier in the year. And corals are forging new relationships with microscopic algae to survive in warmer, more acidic seas.

As the planet continues to warm, evolutionary changes are expected in other species as well — including Homo sapiens. Climate change will alter the internal workings of our bodies in subtle but significant ways and will likely cause a noticeable shift in our appearance.

Inside the body

A warmer climate means malaria, West Nile virus and other diseases long confined primarily to the tropics will spread into temperate zones. As a result, people living in the U.S. and other developed nations will be exposed to these illnesses, and our immune systems will be forced to evolve new defenses. That, in turn, could cause other, noninfectious diseases.

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Two blood disorders — sickle cell and thalassemia — arose and continue to exist because they have a beneficial side effect: resistance to malaria. Such disorders, or new ones, may soon appear if malaria moves into populated areas of North America, East Asia and Europe.

Similarly, our digestive systems will evolve in response to shifts in food availability — where crops and livestock can be cultivated. The ability to digest milk in adulthood evolved among groups in the Middle East and North Africa that began raising cattle. Future generations may evolve better abilities to tolerate sugar or fat.

Changing diets will also trigger changes in our microbiomes — the bacteria and other microorganisms that live in our guts and help to keep us healthy. Vegetarians tend to harbor a different mix of bacteria than meat eaters, and these changes could be exaggerated if prolonged droughts make it too costly to raise livestock for meat.

External changes

While these changes will be of enormous interest to biologists, they will be largely invisible. But as we change on the inside, we’ll also be changing on the outside. Evidence suggests that a warming planet could melt away differences between human races — or population groups, as scientists more accurately call them.

The reason why climate change could reduce racial differences is that it will trigger massive migrations. In recent decades the world has become more urbanized, with people moving into large cities in coastal areas. But as polar ice melts and sea levels rise, large numbers of people will be forced to flee the coasts. And as droughts become more common and more severe, people living in more arid areas will have to move to places with more reliable sources of water.

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These migrations will erode the geographic barriers that once separated human populations. In fact, this process is already underway. As of 2017, 258 million people were living in a country other than the one they were born in — an increase of 49 percent since 2000, according to a report from the United Nations. A World Bank report released in March predicts that climate change will cause 140 million people to migrate by 2050, with those now living in sub-Saharan Africa, South Asia and Latin America especially likely to migrate.

One consequence of large-scale migrations is what biologists call gene flow, a type of evolution caused by the blending of genes between populations. When people from different populations mate and reproduce, their genes intermingle in their children. That can lead to combinations of traits not seen in either parent or in the populations they come from — like the dark skin and blue eyes of Cape Verde islanders, the result of interbreeding between Portuguese and West Africans.

Shifting skin color

One of the most obvious effects of gene flow may be greater similarity in skin color.

Skin color differences came about a result of natural selection in different human populations. The pigment eumelanin makes skin darker, which helps protect against harsh sunlight. But too much eumelanin can make it hard for the body to produce vitamin D, which is needed to build healthy bones. So over many thousands of years, human populations evolved varying levels of skin pigmentation as they spread across the globe, with natural selection balancing the cost of having too much eumelanin (which can indirectly cause bone deformities) versus having too little (which can lead to cancer and birth defects).

As a result, skin color came to closely match the intensity of sunlight in different regions — darker near the equator and lighter near the poles.

But in today’s world, with sunscreen and vitamin supplements, natural selection is less relevant to ongoing changes in human skin pigmentation than gene flow. Because skin color is controlled by many genes, parents whose skin color differs tend to have children with intermediate skin tones. And so in five to 10 generations (125 to 250 years), we may see fewer people with dark skin or pale skin and more with a brown or olive complexion. Having both dark skin and light eyes may become more common.

Blending of races is already well underway in ethnically diverse countries like Brazil, Singapore and the U.S. A Pew report from 2017 found that the number of multiracial births in the U.S. rose from 1 percent in 1970 to 10 percent in 2013. And the increase will continue — the multiracial population is projected to grow by 174 percent over the next four decades.

The bottom line? As people around the world become more physically similar to one another, it's possible that racism might slowly fade.

Scott Solomon teaches ecology, evolution and scientific communication at Rice University. He is the author of "Future Humans: Inside the Science of Our Continuing Evolution."


Are there animals that have evolved a resistance to human activity or encroachment? - Biology

There is not one gene, trait, or characteristic that distinguishes all members of one race from all members of another. We can map any number of traits and none would match our idea of race. This is because modern humans haven't been around long enough to evolve into different subspecies and we've always moved, mated, and mixed our genes. Beneath the skin, we are one of the most genetically similar of all species.

Lots of animals are divided into subspecies. Why doesn't it make sense to group humans the same way?

Subspecies are animal groups that are related, can interbreed, and yet have characteristics that make them distinct from one another. Two basic ingredients are critical to the development of separate subspecies: isolation and time. Unlike most animals, humans are a relatively young species and we are extremely mobile, so we simply haven't evolved into different subspecies.

The earliest hominids evolved from apes about 5 million years ago, but modern humans (Homo sapien sapiens) didn't emerge until 150,000-200,000 years ago in eastern Africa, where we spent most of our evolution together as a species. Our species first left Africa only about 50,000-100,000 years ago and quickly spread across the entire world. All of us are descended from these recent African ancestors.

Many other animal species have been around much longer or they have shorter life spans, so they've had many more opportunities to accumulate genetic variants. Penguins, for example, have twice as much genetic diversity as humans. Fruit flies have 10 times as much. Even our closest living relative, the chimpanzee, has been around at least several million years. There's more genetic diversity within a group of chimps on a single hillside in Gomba than in the entire human species.

Domesticated animals such as dogs also have a lot of genetic diversity, but this is mostly due to selective breeding under controlled conditions. Humans, on the other hand, have always mixed freely and widely. As a result, we're all mongrels: Eighty-five percent of all human variation can be found in any local population, whether they be Kurds, Icelanders, Papua New Guineans, or Mongolians. Ninety-four percent can be found on any continent.

Animals are also limited by habitat and geographical features such as rivers and canyons, so it is easy for groups to become isolated and genetically distinct from one another. Humans, on the other hand, are much more adaptable and have not been limited by geography in the same way. Early on, we could ford rivers, cross canyons, move great distances over a relatively short time, and modify our environment to fit our needs. We are also extremely mobile as a species. Even the remotest island tribe in the Pacific originally came from elsewhere and maintained some contact with neighboring groups.

We may think global migration is a recent phenomenon, but it has characterized most of human history. Whether we're moving halfway around the world or from one village to another, the passage of genes takes place under many circumstances, large scale and small: migration, wars, trade, slave-taking, rape, and exogamous marriage (marriage with "outsiders").

It takes a long time to accumulate a lot of genetic variation, because new variants arise only through mutation - copying errors from one generation to the next. On the other hand, it takes just a very small amount of migration - one individual in each generation moving from one village to another and reproducing - to prevent groups from becoming genetically distinct or isolated. Humans just haven't evolved into distinct subgroups.


But I can see obvious differences between people - don't those translate into deeper differences, like propensity for certain diseases?

The visual differences we are attuned to don't tell us anything about what's beneath the skin. This is because human variation is highly non-concordant. Most traits are influenced by different genes, so they're inherited independently, not grouped into the few packages we call races. In other words, the presence of one trait doesn't guarantee the presence of another. Can you tell a person's eye color from their height? What about their blood type from the size of their head? What about subtler things like a person's ability to play sports or their mathematical skills? It doesn't make sense to talk about group racial characteristics, whether external or internal.

Genetic differences do exist between people, but it is more accurate to speak of ancestry, rather than race, as the root of inherited diseases or conditions. Not everyone who looks alike or lives in the same region shares a common ancestry, so using "race" as a shorthand for ancestry can be misleading. Sickle cell, for example, often thought of as a "racial" disease afflicting Africans, is actually a gene that confers resistance to malaria, so it occurs in areas such as central and western Africa, the Mediterranean, and Arabia, but not in southern Africa. In medicine, a simplistic view can lead to misdiagnoses, with fatal consequences. Racial "profiling" isn't appropriate on the New Jersey Turnpike or in the doctor's office. As evolutionary biologist Joseph Graves reminds us, medicine should treat individuals, not groups.

On the other hand, the social reality of race can have biological effects. Native Americans have the highest rates of diabetes and African American men die of heart disease five times more often than white men. But is this a product of biology or social conditions? How do you measure this relationship or even determine who is Native American or African American on a genetic level? Access to medical care, health insurance, and safe living conditions can certainly affect medical outcomes. So can the stress of racism. But the reasons aren't innate or genetic.

Believing in race as biology allows us to overlook the social factors that contribute to inequality. Understanding that race is socially constructed is the first step in addressing those factors and giving everyone a fair chance in life.

The Resources section of this Web site contains a wealth of information about issues related to race. There you'll find detailed information about books, organizations, film/videos, and other Web sites. For more about this topic, search under "human variation," "evolution," "genetics" and "biology." You can also read related online articles in the Background Readings section of this site.

    Map your family tree. How far back can you go? How do the number of known ancestors compare to the number of unknown?


Contents

The term habitat fragmentation includes five discrete phenomena:

  • Reduction in the total area of the habitat
  • Decrease of the interior: edge ratio
  • Isolation of one habitat fragment from other areas of habitat
  • Breaking up of one patch of habitat into several smaller patches
  • Decrease in the average size of each patch of habitat

"fragmentation . not only causes loss of the amount of habitat but by creating small, isolated patches it also changes the properties of the remaining habitat" (van den Berg et al. 2001) [ failed verification ] . Habitat fragmentation is the landscape level of the phenomenon, and patch level process. Thus meaning, it covers the patch areas, edge effects, and patch shape complexity. [4]

In scientific literature, there is some debate whether the term "habitat fragmentation" applies in cases of habitat loss, or whether the term primarily applies to the phenomenon of habitat being cut into smaller pieces without significant reduction in habitat area. Scientists who use the stricter definition of "habitat fragmentation" per se [3] would refer to the loss of habitat area as "habitat loss" and explicitly mention both terms if describing a situation where the habitat becomes less connected and there is less overall habitat.

Furthermore, habitat fragmentation is considered as an invasive threat to biodiversity, due to its implications of affecting large number of species than biological invasions, overexploitation, or pollution. [5]

Additionally, the effects of habitat fragmentation damage the ability for species, such as native plants, to be able to effectively adapt to their changing environments. Ultimately, this prevents gene flow from one generation of population to the next, especially for species living in smaller population sizes. Whereas, for species of larger populations have more genetic mutations which can arise and genetic recombination impacts which can increase species survival in those environments. Overall, habitat fragmentation results in habitat disintegration and habitat loss which both tie into destructing biodiversity as a whole.

Natural causes Edit

Evidence of habitat destruction through natural processes such as volcanism, fire, and climate change is found in the fossil record. [1] [ failed verification ] For example, habitat fragmentation of tropical rainforests in Euramerica 300 million years ago led to a great loss of amphibian diversity, but simultaneously the drier climate spurred on a burst of diversity among reptiles. [1]

Human causes Edit

Habitat fragmentation is frequently caused by humans when native plants are cleared for human activities such as agriculture, rural development, urbanization and the creation of hydroelectric reservoirs. Habitats which were once continuous become divided into separate fragments. After intensive clearing, the separate fragments tend to be very small islands isolated from each other by cropland, pasture, pavement, or even barren land. The latter is often the result of slash and burn farming in tropical forests. In the wheat belt of central-western New South Wales, Australia, 90% of the native vegetation has been cleared and over 99% of the tall grass prairie of North America has been cleared, resulting in extreme habitat fragmentation.

Endogenous vs. exogenous Edit

There are two types of processes that can lead to habitat fragmentation. There are exogenous processes and endogenous processes. Endogenous is a process that develops as a part of species biology so they typically include changes in biology, behavior, and interactions within or between species. Endogenous threats can result in changes to breeding patterns or migration patterns and are often triggered by exogenous processes. Exogenous processes are independent of species biology and can include habitat degradation, habitat subdivision or habitat isolation. These processes can have a substantial impact on endogenous processes by fundamentally altering species behavior. Habitat subdivision or isolation can lead to changes in dispersal or movement of species including changes to seasonal migration. These changes can lead to a decrease in a density of species, increased competition or even increased predation. [6]

Habitat and biodiversity loss Edit

One of the major ways that habitat fragmentation affects biodiversity is by reducing the amount of suitable habitat available for organisms. Habitat fragmentation often involves both habitat destruction and the subdivision of previously continuous habitat. [7] Plants and other sessile organisms are disproportionately affected by some types of habitat fragmentation because they cannot respond quickly to the altered spatial configuration of the habitat. [8]

Habitat loss, which can occur through the process of habitat fragmentation, is considered to be the greatest threat to species. [9] But, the effect of the configuration of habitat patches within the landscape, independent of the effect of the amount of habitat within the landscape (referred to as fragmentation per se [3] ), has been suggested to be small. [10] A review of empirical studies found that, of the 381 reported significant effect of habitat fragmentation per se on species occurrences, abundances or diversity in the scientific literature, 76% were positive whereas 24% were negative. [11] Despite these results, the scientific literature tends to emphasize negative effects more than positive effects. [12] Positive effects of habitat fragmentation per se imply that several small patches of habitat can have higher conservation value than a single large patch of equivalent size. [11] Land sharing strategies could therefore have more positive impacts on species than land sparing strategies. [11]

Area is the primary determinant of the number of species in a fragment [13] and the relative contributions of demographic and genetic processes to the risk of global population extinction depend on habitat configuration, stochastic environmental variation and species features. [14] Minor fluctuations in climate, resources, or other factors that would be unremarkable and quickly corrected in large populations can be catastrophic in small, isolated populations. Thus fragmentation of habitat is an important cause of species extinction. [13] Population dynamics of subdivided populations tend to vary asynchronously. In an unfragmented landscape a declining population can be "rescued" by immigration from a nearby expanding population. In fragmented landscapes, the distance between fragments may prevent this from happening. Additionally, unoccupied fragments of habitat that are separated from a source of immigrants by some barrier are less likely to be repopulated than adjoining fragments. Even small species such as the Columbia spotted frog are reliant on the rescue effect. Studies showed 25% of juveniles travel a distance over 200m compared to 4% of adults. Of these, 95% remain in their new locale, demonstrating that this journey is necessary for survival. [15]

Additionally, habitat fragmentation leads to edge effects. Microclimatic changes in light, temperature, and wind can alter the ecology around the fragment, and in the interior and exterior portions of the fragment. [16] Fires become more likely in the area as humidity drops and temperature and wind levels rise. Exotic and pest species may establish themselves easily in such disturbed environments, and the proximity of domestic animals often upsets the natural ecology. Also, habitat along the edge of a fragment has a different climate and favours different species from the interior habitat. Small fragments are therefore unfavourable for species that require interior habitat. The percentage preservation of contiguous habitats is closely related to both genetic and species biodiversity preservation. Generally a 10% remnant contiguous habitat will result in a 50% biodiversity loss. [17]

Much of the remaining terrestrial wildlife habitat in many third world countries has experienced fragmentation through the development of urban expansion such as roads interfering with habitat loss. Aquatic species’ habitats have been fragmented by dams and water diversions. [18] These fragments of habitat may not be large or connected enough to support species that need a large territory where they can find mates and food. The loss and fragmentation of habitats makes it difficult for migratory species to find places to rest and feed along their migration routes. [18]

Informed conservation Edit

Habitat fragmentation is often a cause of species becoming threatened or endangered. [19] The existence of viable habitat is critical to the survival of any species, and in many cases, the fragmentation of any remaining habitat can lead to difficult decisions for conservation biologists. Given a limited amount of resources available for conservation is it preferable to protect the existing isolated patches of habitat or to buy back land to get the largest possible contiguous piece of land. In rare cases, a conservation reliant species may gain some measure of disease protection by being distributed in isolated habitats, and when controlled for overall habitat loss some studies have shown a positive relationship between species richness and fragmentation this phenomenon has been called the habitat amount hypothesis, though the validity of this claim has been disputed. [10] [20] The ongoing debate of what size fragments are most relevant for conservation is often referred to as SLOSS (Single Large or Several Small).

One solution to the problem of habitat fragmentation is to link the fragments by preserving or planting corridors of native vegetation. In some cases, a bridge or underpass may be enough to join two fragments. [21] This has the potential to mitigate the problem of isolation but not the loss of interior habitat.

Another mitigation measure is the enlargement of small remnants to increase the amount of interior habitat. This may be impractical since developed land is often more expensive and could require significant time and effort to restore.

The best solution is generally dependent on the particular species or ecosystem that is being considered. More mobile species, like most birds, do not need connected habitat while some smaller animals, like rodents, may be more exposed to predation in open land. These questions generally fall under the headings of metapopulations island biogeography.

Genetic risks Edit

As the remaining habitat patches are smaller, they tend to support smaller populations of fewer species. [22] Small populations are at an increased risk of a variety of genetic consequences that influence their long-term survival. [23] Remnant populations often contain only a subset of the genetic diversity found in the previously continuous habitat. In these cases, processes that act upon underlying genetic diversity, such as adaptation, have a smaller pool of fitness-maintaining alleles to survive in the face of environmental change. However in some scenarios, where subsets of genetic diversity are partitioned among multiple habitat fragments, almost all original genetic diversity can be maintained despite each individual fragment displaying a reduced subset of diversity. [24]

Gene Flow and Inbreeding Edit

Gene flow occurs when individuals of the same species exchange genetic information through reproduction. Populations can maintain genetic diversity through migration. When a habitat becomes fragmented and reduced in area, gene flow and migration are typically reduced. Fewer individuals will migrate into the remaining fragments, and small disconnected populations that may have once been part of a single large population will become reproductively isolated. Scientific evidence that gene flow is reduced due to fragmentation depends on the study species. While trees that have long-range pollination and dispersal mechanisms may not experience reduced gene flow following fragmentation, [25] most species are at risk of reduced gene flow following habitat fragmentation. [8]

Reduced gene flow, and reproductive isolation can result in inbreeding between related individuals. Inbreeding does not always result in negative fitness consequences, but when inbreeding is associated with fitness reduction it is called inbreeding depression. Inbreeding becomes of increasing concern as the level of homozygosity increases, facilitating the expression of deleterious alleles that reduce the fitness. Habitat fragmentation can lead to inbreeding depression for many species due to reduced gene flow. [26] [27] Inbreeding depression is associated with conservation risks, like local extinction. [28]

Genetic drift Edit

Small populations are more susceptible to genetic drift. Genetic drift is random changes to the genetic makeup of populations and leads to reductions in genetic diversity. The smaller the population is, the more likely genetic drift will be a driving force of evolution rather than natural selection. Because genetic drift is a random process, it does not allow species to become more adapted to their environment. Habitat fragmentation is associated with increases to genetic drift in small populations which can have negative consequences for the genetic diversity of the populations. [26] However, research suggests that some tree species may be resilient to the negative consequences of genetic drift until population size is as small as ten individuals or less. [24]

Genetic consequences of habitat fragmentation for plant populations Edit

Habitat fragmentation decreases the size and increases plant populations' spatial isolation. With genetic variation and increased methods of inter-population genetic divergence due to increased effects of random genetic drift, elevating inbreeding and reducing gene flow within plant species. While genetic variation may decrease with remnant population size, not all fragmentation events lead to genetic losses and different types of genetic variation. Rarely, fragmentation can also increase gene flow among remnant populations, breaking down local genetic structure. [29]

Adaptation Edit

In order for populations to evolve in response to natural selection, they must be large enough that natural selection is a stronger evolutionary force than genetic drift. Recent studies on the impacts of habitat fragmentation on adaptation in some plant species have suggested that organisms in fragmented landscapes may be able to adapt to fragmentation. [30] [31] However, there are also many cases where fragmentation reduces adaptation capacity because of small population size. [32]

Examples of impacted species Edit

Some species that have experienced genetic consequences due to habitat fragmentation are listed below:

  • Macquaria australasica[26][33]
  • Fagus sylvatica[34]
  • Betula nana[24]
  • Rhinella ornata[35]
  • Ochotona princeps[36]
  • Uta stansburiana[37]
  • Plestiodon skiltonianus[37]
  • Sceloporus occidentalis[37]
  • Chamaea fasciata[37]

Effect on animal behaviours Edit

Although the way habitat fragmentation affects the genetics and extinction rates of species has been heavily studied, fragmentation has also been shown to affect species' behaviours and cultures as well. This is important because social interactions can determine and have an effect on a species' fitness and survival. Habitat fragmentation alters the resources available and the structure of habitats, as a result, alters the behaviours of species and the dynamics between differing species. Behaviours affected can be within a species such as reproduction, mating, foraging, species dispersal, communication and movement patterns or can be behaviours between species such as predator-prey relationships. [38] In addition, when animals happen to venture into unknown areas in between fragmented forests or landscapes, they can supposedly come into contact with humans which puts them at a great risk and further decreases their chances of survival. [5]

Predation behaviours Edit

Habitat fragmentation due to anthropogenic activities has been shown to greatly affect the predator-prey dynamics of many species by altering the number of species and the members of those species. [38] This affects the natural predator-prey relationships between animals in a given community [38] and forces them to alter their behaviours and interactions, therefore resetting the so-called "behavioral space race". [39] The way in which fragmentation changes and re-shapes these interactions can occur in many different forms. Most prey species have patches of land that are a refuge from their predators, allowing them the safety to reproduce and raise their young. Human introduced structures such as roads and pipelines alter these areas by facilitating predator activity in these refuges, increasing predator-prey overlap. [39] The opposite could also occur in the favour of prey, increasing prey refuge and subsequently decreasing predation rates. Fragmentation may also increase predator abundance or predator efficiency and therefore increase predation rates in this manner. [39] Several other factors can also increase or decrease the extent to which the shifting predator-prey dynamics affect certain species, including how diverse a predators diet is and how flexible habitat requirements are for predators and prey. [38] Depending on which species are affected and these other factors, fragmentation and its effects on predator-prey dynamics may contribute to species extinction. [38] In response to these new environmental pressures, new adaptive behaviours may be developed. Prey species may adapt to increased risk of predation with strategies such as altering mating tactics or changing behaviours and activities related to food and foraging. [38]

Boreal woodland caribous Edit

In the boreal woodland caribous of British Columbia, the effects of fragmentation are demonstrated. The species refuge area is peatland bog which has been interrupted by linear features such as roads and pipelines. [40] These features have allowed their natural predators, the wolf, and the black bear to more efficiently travel over landscapes and between patches of land. [40] Since their predators can more easily access the caribous' refuge, the females of the species attempt to avoid the area, affecting their reproductive behaviours and offspring produced. [40]

Communication behaviours Edit

Fragmentation affecting the communication behaviours of birds has been well studied in Dupont's Lark. The Larks primarily reside in regions of Spain and are a small passerine bird which uses songs as a means of cultural transmission between members of the species. [40] The Larks have two distinct vocalizations, the song, and the territorial call. The territorial call is used by males to defend and signal territory from other male Larks and is shared between neighbouring territories when males respond to a rivals song. [41] Occasionally it is used as a threat signal to signify an impending attack on territory. [42] A large song repertoire can enhance a male's ability to survive and reproduce as he has a greater ability to defend his territory from other males, and a larger number of males in the species means a larger variety of songs being transmitted. [41] Fragmentation of the Dupont's Lark territory from agriculture, forestry and urbanization appears to have a large effect on their communication structures. [42] Males only perceive territories of a certain distance to be rivals and so isolation of territory from others due to fragmentation leads to a decrease in territorial calls as the males no longer have any reason to use it or have any songs to match. [42]

Humans have also brought on varying implications into ecosystems which in turn affect animal behaviour and responses generated. [43] Although there are some species which are able to survive these kinds of harsh conditions, such as, cutting down wood in the forests for pulp and paper industries, there are animals which can survive this change but some that cannot. An example includes, varying aquatic insects are able to identify appropriate ponds to lay their eggs with the aid of polarized light to guide them, however, due to ecosystem modifications caused by humans they are led onto artificial structures which emit artificial light which are induced by dry asphalt dry roads for an example. [44]

Effect on microorganisms Edit

While habitat fragmentation is often associated with its effects on large plant and animal populations and biodiversity, due to the interconnectedness of ecosystems there are also significant effects that it has on the microbiota of an environment. Increased fragmentation has been linked to reduced populations and diversity of fungi responsible for decomposition, as well as the insects they are host to. [45] This has been linked to simplified food webs in highly fragmented areas compared to old growth forests. [46] Furthermore, edge effects have been shown to result in significantly varied microenvironments compared to interior forest due to variations in light availability, presence of wind, changes in precipitation, and overall moisture content of leaf litter. [47] These microenvironments are often not conducive to overall forest health as they enable generalist species to thrive at the expense of specialists that depend on specific environments. [45]

Forest fragmentation is a form of habitat fragmentation where forests are reduced (either naturally or man-made) to relatively small, isolated patches of forest known as forest fragments or forest remnants. [1] The intervening matrix that separates the remaining woodland patches can be natural open areas, farmland, or developed areas. Following the principles of island biogeography, remnant woodlands act like islands of forest in a sea of pastures, fields, subdivisions, shopping malls, etc. These fragments will then begin to undergo the process of ecosystem decay.

Forest fragmentation also includes less subtle forms of discontinuities such as utility right-of-ways (ROWs). Utility ROWs are of ecological interest because they have become pervasive in many forest communities, spanning areas as large as 5 million acres in the United States. [48] Utility ROWs include electricity transmission ROWs, gas pipeline and telecommunication ROWs. Electricity transmission ROWs are created to prevent vegetation interference with transmission lines. Some studies have shown that electricity transmission ROWs harbor more plant species than adjoining forest areas, [49] due to alterations in the microclimate in and around the corridor. Discontinuities in forest areas associated with utility right-of-ways can serve as biodiversity havens for native bees [48] and grassland species, [50] as the right-of-ways are preserved in an early successional stage.

Forest fragmentation reduces food resources and habitat sources for animals thus splitting these species apart. Thus, making these animals become much more susceptible to effects of predation and making them less likely to perform interbreeding - lowering genetic diversity. [51]

Implications Edit

Forest fragmentation is one of the greatest threats to biodiversity in forests, especially in the tropics. [52] The problem of habitat destruction that caused the fragmentation in the first place is compounded by:

  • the inability of individual forest fragments to support viable populations, especially of large vertebrates
  • the local extinction of species that do not have at least one fragment capable of supporting a viable population that alter the conditions of the outer areas of the fragment, greatly reducing the amount of true forest interior habitat. [53]

The effect of fragmentation on the flora and fauna of a forest patch depends on a) the size of the patch, and b) its degree of isolation. [54] Isolation depends on the distance to the nearest similar patch, and the contrast with the surrounding areas. For example, if a cleared area is reforested or allowed to regenerate, the increasing structural diversity of the vegetation will lessen the isolation of the forest fragments. However, when formerly forested lands are converted permanently to pastures, agricultural fields, or human-inhabited developed areas, the remaining forest fragments, and the biota within them, are often highly isolated.

Forest patches that are smaller or more isolated will lose species faster than those that are larger or less isolated. A large number of small forest "islands" typically cannot support the same biodiversity that a single contiguous forest would hold, even if their combined area is much greater than the single forest. However, forest islands in rural landscapes greatly increase their biodiversity. [55] In the Maulino forest of Chile fragmentation appear to not affect overall plant diversity much, and tree diversity is indeed higher in fragments than in large continuous forests. [56] [57]

McGill University in Montreal, Quebec, Canada released a university based newspaper statement stating that 70% of the world’s remaining forest stands within one kilometre of a forest edge putting biodiversity at an immense risk based on research conducted by international scientists. [58]

Reduced fragment area, increased isolation, and increased edge initiate changes that percolate through all ecosystems. Habitat fragmentation is able to formulate persistent outcomes which can also become unexpected such as an abundance of some species and the pattern that long temporal scales are required to discern many strong system responses. [5]

Sustainable forest management Edit

The presence of forest fragments influences the supply of various ecosystems in adjacent agricultural fields (Mitchell et al. 2014). Mitchell et al (2014), researched on six varying ecosystem factors such as crop production, decomposition, pesticide regulation, carbon storage, soil fertility, and water quality regulation in soybean fields through separate distances by nearby forest fragments which all varied in isolation and size across an agricultural landscape in Quebec, Canada. Sustainable forest management can be achieved in several ways including by managing forests for ecosystem services (beyond simple provisioning), through government compensation schemes, and through effective regulation and legal frameworks. [59] The only realistic method of conserving forests is to apply and practice sustainable forest management to risk further loss.

There is a high industrial demand for wood, pulp, paper, and other resources which the forest can provide with, thus businesses which will want more access to the cutting of forests to gain those resources. The rainforest alliance has efficiently been able to put into place an approach to sustainable forest management, and they established this in the late 1980s. Their conservation was deemed successful as it has saved over nearly half a billion acres of land around the world. [60]

A few approaches and measures which can be taken in order to conserve forests are methods by which erosion can be minimized, waste is properly disposed, conserve native tree species to maintain genetic diversity, and setting aside forestland (provides habitat for critical wildlife species). [60] Additionally, forest fires can also occur frequently and measures can also be taken to further prevent forest fires from occurring. For example, in Guatemala’s culturally and ecologically significant Petén region, researchers were able to find over a 20-year period, actively managed FSC-certified forests experienced substantially lower rates of deforestation than nearby protected areas, and forest fires only affected 0.1 percent of certified land area, compared to 10.4 percent of protected areas. [60] However, it must be duly noted that short term decisions regarding forest sector employment and harvest practices can have long-term effects on biodiversity. [61] Planted forests become increasingly important as they supply approximately a quarter of global industrial roundwood production and are predicted to account for 50% of global output within two decades (Brown, 1998 Jaakko Poyry, 1999). [62] Although there have been many difficulties, the implementation of forest certification has been quite prominent in being able to raise effective awareness and disseminating knowledge on a holistic concept, embracing economic, environmental and social issues, worldwide. While also providing a tool for a range of other applications than assessment of sustainability, such as e.g. verifying carbon sinks. [63]

Two approaches are typically used to understand habitat fragmentation and its ecological impacts.

Species-oriented approach Edit

The species-oriented approach focuses specifically on individual species and how they each respond to their environment and habitat changes with in it. This approach can be limited because it does only focus on individual species and does not allow for a broad view of the impacts of habitat fragmentation across species. [64]

Pattern-oriented approach Edit

The pattern-oriented approach is based on land cover and its patterning in correlation with species occurrences. One model of study for landscape patterning is the patch-matrix-corridor model developed by Richard Forman The pattern-oriented approach focuses on land cover defined by human means and activities. This model has stemmed from island biogeography and tries to infer causal relationships between the defined landscapes and the occurrence of species or groups of species within them. The approach has limitations in its collective assumptions across species or landscapes which may not account for variations amongst them. [65]

Variegation Model Edit

The other model is the variegation model. Variegated landscapes retain much of their natural vegetation but are intermixed with gradients of modified habitat [66] This model of habitat fragmentation typically applies to landscapes that are modified by agriculture. In contrast to the fragmentation model that is denoted by isolated patches of habitat surrounded by unsuitable landscape environments, the variegation model applies to landscapes modified by agriculture where small patches of habitat remain near the remnant original habitat. In between these patches are a matrix of grassland that is often modified versions of the original habitat. These areas do not present as much of a barrier to native species. [67]


The Institute for Creation Research

Often the claim is made in biology classes that evolution has been observed in certain microbes&mdashgerms that over time have developed a resistance to antibiotics. For instance, penicillin is generally now less effective than before. Stronger and more focused drugs have been developed, each with initial benefits, but which must continue to be replaced with something stronger. Now, "super germs" defy treatment.

One might ask, have these single-celled germs "evolved"? And does this prove that single-celled organisms evolved into plants and people?

As is frequently the case, we must first distinguish between variation, adaptation, and recombination of existing traits (i.e., microevolution) and the appearance of new and different genes, body parts, and traits (i.e., macroevolution). Does this acquired resistance to antibiotics, this population shift, this dominant exhibition of a previously minority trait point to macroevolution? Since each species of germ remained that same species and nothing new was produced, the answer is no!

Here's how it works. In a given population of bacteria, many genes are present which express themselves in a variety of ways. In a natural environment, the genes (and traits) are freely mixed. When exposed to an antibiotic, most of the microbes die. But some, through a fortuitous genetic recombination, possess a resistance to the antibiotic. They are the only ones to reproduce, and their descendants inherit the same genetic resistance. Over time, virtually all possess this resistance. Thus the population has lost the ability to produce individuals with a sensitivity to the antibiotic. No new genetic information was produced indeed, genetic information was lost.

A new line of research has produced tantalizing results. Evidently, when stressed, some microbes go into a mutation mode, rapidly producing a variety of strains, thereby increasing the odds that some will survive the stress. This has produced some interesting areas for speculation by creationists, but it still mitigates against evolution. There is a tremendous scope of genetic potential already present in a cell, but E. coli bacteria before stress and mutation remain E. coli. Minor change has taken place, but not true evolution.

Furthermore, it has been proven that resistance to many modern antibiotics was present decades before their discovery. In 1845, sailors on an ill-fated Arctic expedition were buried in the permafrost and remained deeply frozen until their bodies were exhumed in 1986. Preservation was so complete that six strains of nineteenth-century bacteria found dormant in the contents of the sailors' intestines were able to be revived! When tested, these bacteria were found to possess resistance to several modern-day antibiotics, including penicillin. Such traits were obviously present prior to penicillin's discovery, and thus could not be an evolutionary development. 1

Here's the point. Mutations, adaptation, variation, diversity, population shifts, etc., all occur, but, these are not macroevolutionary changes.

* Dr. John Morris is President of ICR.

Cite this article: Morris, J. 1998. Do Bacteria Evolve Resistance to Antibiotics? Acts & Facts. 27 (10).


Lactose intolerance

Adult lactose intolerance is a global norm, not an exception or an illness. (Piqsels)

Lactose intolerance occurs when we can’t digest milk sugars (lactose) in adulthood. This can cause nausea, cramping, gas and diarrhea, and is considered a medical condition.

Lactose is broken down by the enzyme lactase. Adult production of lactase evolved in human populations that domesticated animals about 10,000 years ago. These populations were found in northern and central Europe, and in pastoral communities in Africa. Milk is a calorie- and nutrient-dense food, meaning that people who could digest lactose would be better nourished, giving them a better chance at survival and reproduction.

Mutations allowing for adult digestion of lactose gradually spread over generations within these populations. However, those with ancestors from populations that did not regularly herd and milk domesticated animals, such as Indigenous populations in North and South America and most Asian populations, do not possess this ability. In fact, roughly 65 per cent of adults worldwide remain lactose intolerant.

If 65 per cent of the global population cannot digest lactose, why is it treated as an illness? There is nothing “wrong” with someone who is lactose intolerant no intervention is needed other than to avoid or limit dairy consumption. Evolution tells us that lactose intolerance is perfectly normal. We simply need to redefine illness.


How Humans Can Influence Evolution of Other Species Scientists recently published an analysis of how humans affect evolution, and why we should care

In biology, evolution is how populations change over time from their common ancestor. This process has been happening on Earth since life first began, over 3.5 billion years ago. Evolution, however is not driven by one factor, but many, from climate conditions to predator/prey relationships. And even now, 3.5 billion years since the start of life, humans may play a bigger role than we imagined in the evolution of other than we could have possibly imagined.

Since Darwin, many papers have been published on how humans affect the evolution of a species. From infections to hunting ground, these papers usually focus on individual specifics rather than the big picture. A recent paper authored by Andrew Hendry, Kiyoko Gotanda, and Erik Svensson cross analysed multiple studies in an attempt to compare and contrast what human related factors influence evolution and how powerful each factor is.

We as a species actively attack other species that we don’t like, such as weeds, bugs, or vermin. These “enemies” are rapidly affected by our animosity towards them and change very quickly in response to our actions. A notable example of this is pesticide resistance, wherein the overuse of pesticides will kill off most unwanted insects, but the few that survive pass on their resistance to their offspring. It is in this way that we breed ever stronger enemy species.

The potential for evolution is directly related to how much variation a species has. The more variation, the more traits there are, and the easier it is for a population to adapt to a change in the environment. For example, if all individuals in a population are the same, they will be harmed by the same things. This leaves the whole population susceptible to the same fate. Variation means that there will be at least some survivors when something happens. Any change can be a selection pressure. Examples include natural disasters, introduction of new species, or changing the land – either to develop it or to let it go wild.

This is a popular example used in biology textbooks to show how a selection pressure may occur. This is a simplified example of the reality, which is always more complicated than this. Credit: Sciworthy

Besides population, human activity can also affect the the food chain in an ecosystem. When humans create a disturbance in one population it may only affect a few species. But the disruption in those species then affects even more species that interact with it, branching out in a domino effect-like disruption. The addition of a invasive species to an area can lead to new roles for native species who evolve to exploit them. Alternatively, the removal or decrease of a species in an ecosystem will minimize roles that other species can have. In an area where the main prey of ticks have been killed off, the tick population will decrease, decreasing the population of whatever preyed on the ticks, and so on.

The authors argue that it is especially important to keep a watch on our influence of the evolution of other species, not just to maintain biodiversity, but as a means of self-preservation. If left unchecked, they say, enemy or invasive organisms could evolve immunity to our killing methods or hunted animals could evolve to sizes that make them undesirable to hunt. Furthermore, many natural cycles that we rely on to survive, such as the carbon cycle or purification of air, could be disrupted when key organisms no longer play their part.

Concluding on a lighter note, however, the authors mention that actions can and are being taken to help prevent the unwanted evolution of populations. To give endangered populations the best chance for individual variation in the future, breeding is assisted and controlled. One of our biggest enemy species are bacteria and viruses whose rapid evolution regularly reduces the efficacy of antibiotics and vaccines. To combat this drug cocktails are administered to help prevent the rapid evolution of infections. And fisheries are actively monitored to prevent populations from diminishing in size, when before only the largest were caught before they could breed. And the more we learn about how our activities affect the evolution of other populations, the better we can control and prevent undesired outcomes.