Gone Too Soon:
How Does One Reverse the Destruction of Diversity in a Fragmented Habitat?
Elizabeth A. Wash, Salisbury University
Abstract: Every species relies on genetic diversity to evolve, adapt, and avoid extinction, making it of utmost importance to protect genetic diversity and maintain habitats as a whole. If one species is affected, it will create a chain reaction that will impact all species, ultimately creating damage that affects the human race. The question is what effect does habitat fragmentation have on genetic diversity and can destruction be reversed, or will it create an irreversible change that prevents further adaptive success? Research helps determine the effects of habitat loss and fragmentation on genetic diversity and the effects that fragmentation will have on ecosystems. If the ecosystem is altered, it will prevent the ecosystem from carrying out services that are beneficial for humans. With habitat protection and preventive processes implemented, the damage that has the potential to create a vulnerability for at-risk species can be changed to create adaptive success, and bring species back from the brink of extinction. The preventative measures could be limiting deforestation and placing habitats under non-development zones. To reverse habitat fragmentation, there could be corridors built to allow the organisms to venture from one habitat to another, enabling gene flow. A reversal of habitat fragmentation could also be implementing a restructure, where certain populations are removed and placed into a similar habitat, which is not isolated to allow for the rebuilding of adaptive and evolutionary traits. Habitat fragmentation is destroying genetic diversity and must be prevented, for the benefit of all organisms that call Earth home.
Keywords
Climate Change; Habitat Fragmentation; Genetics; Traits; Genetic Diversity; Habitat Protection; Ecosystem; Variability
Acknowledgments
The author wishes to thank Clarke Honor’s College at Salisbury University for supporting the research conducted and providing a course allowing students to conduct research. The author also wishes to thank the professors that proofread previous drafts of this paper. The NRHC organization, which provides these valuable experiences for undergraduate students, is also deserving of thanks. Finally, the author would especially like to thank Dr. Jennifer Nyland for guiding this research endeavor and being an excellent mentor.
Introduction
Plants and animals of all species depend and rely on habitats to nurture their species and to allow them to adapt and evolve. When a habitat is disrupted or damaged, this causes the uprooting of an entire species that called that particular niche their home, which in turn generates an imbalance within the ecosystem that can ultimately result in the extinction of the entire species. Species thrive and evolve right alongside the evolution of their environment, allowing for the nurturing of growth and protection of the fragile genetics that each species carries. Habitats must nurture growth in an organism and protect the fragile genetics that each species carries and stores for generations to come. Habitats allow for the genetic diversity to evolve within each species, creating variability that makes it harder for the species to become vulnerable or extinct. Genetic diversity is vital to species adaptation, evolution, and survivorship because damage to genetic diversity could be detrimental to a species.
When habitats are disrupted, this destroys species by causing inbreeding and reduced gene flow, and can make it difficult for the species to evolve to become compatible with a new environment and to ultimately survive. The loss or fragmentation of habitats will affect the species to a point that is beyond comparison, causing them to become vulnerable and in danger of potential extinction. It is by human intervention that most destruction occurs within these environments, which uproots these organisms, destroys their food, and separates the species that once lived and contributed to the ecosystem. With all of the constant damage to habitats, there is irreversible damage to the inhabitants. Showing that it is important for habitats in all ecosystems to be preserved and saved, could prevent any future damage to the genetic variability of species everywhere.
Background
Habitat loss and fragmentation are often caused by the effects of climate change and by human intervention, without any regard to the species, plants, and animals that call these ecosystems home. The genetic diversity that is within these species is typically nurtured by the habitat in which they live, so when a habitat is destroyed, it also destroys the genetic diversity of a species. This is displayed through the example of the Dianthus carthusianorum, a calcareous grassland plant. The gene flow was minimized through isolation from habitat fragmentation which then caused the calcareous plant to suffer from an increased level of inbreeding, resulting in a population that was vulnerable to extinction (Reisch, et al., 2017). As seen with the D. carthusianorum, the human interferences of deforestation and increased urban development caused the habitat to have a loss of about 80%, ultimately intensifying the ability to adapt and evolve within this organism (Reisch et al., 2017). All species rely on a specific habitat to comfortably live in and thrive, so when the environment in which they once were able to thrive is taken away or destroyed, it displaces these species.
When a species becomes severely displaced, it contributes to the species inability to continue to develop which limits their genetic diversity, and can potentially cause extinction. An example of this stunted development can be found in the Heliconius hatteren and H. hermathena butterflies of Brazil, where a loss in habitat due to logging and climate change resulted in a population bottleneck, meaning that the organism was unable to develop any more variability causing a majority of the species to die and leaving the surviving individuals vulnerable (Massardo, et al., 2020). The question is how does habitat fragmentation affect the development of genetic diversity within a species? When a species becomes displaced, does this affect the genetic diversity of just that generation or for generations to come? Will the species as a whole suffer this loss on a genetic level or just those in the certain area that was destroyed? Habitat loss and fragmentation do more than just destroy the area that a species once called home; it completely changes the species on a genetic level, causing damage that can never be replaced or undone (Gómez-Fernández, et al., 2016). To understand the direct correlation of habitat fragmentation and the extensive loss that is suffered to the genetic diversity of species, research must be conducted to determine what precautionary and protective measures can be put in place to protect these vulnerable species. The research conducted can include four major methods: documentation of fragmented habitats and the effects of isolation on the organisms, measurement of the differences in the genetic structure before and after destruction, comparison of traits in an organism to its common ancestor, or comparison of traits present before habitat fragmentation to current results.
Significance
The original key terms and concepts that were used as a baseline for this research included words such as climate change, habitat loss, and fragmentation which brought up numerous sources, showing the magnitude of this broad and compelling research. The significance of this paper is to provide additional research to this field of habitat loss and fragmentation, as well as to link together varying ideas about the cause of genetic destruction and potential solutions. This paper indicates that there is a need for the protection of all habitats, environments, and ecosystems, to save all species, and not put them into vulnerable positions. If there was no protection for these environments, then many species would become extinct, which would create a catastrophic chain reaction across the entire ecosystem. With the use of information already known about the negative side effects of habitat loss and fragmentation, the conclusions found within this research will provide helpful solutions to the presented problem. This will also add a point of view from a genetic level that could be universally applied, while not being specific to one species. A genetic point of view is important, because it can explain what happens to species, and can lead to an explanation for when species become vulnerable or virtually extinct. If there is understanding about what could potentially be damaging these species genetically, then there can be preventative procedures put in place to try and preserve all species’ genetic diversity from destruction.
While this paper is extremely important to the scientific community, it is of importance in human’s daily life. For example, if an environment where a certain food was grown and processed was destroyed, humanity could be faced with the beginnings of a food shortage (Liao, et al., 2017). This food shortage could then lead to a decrease in the human population. Another example of the issues that could arise from a loss of habitat or fragmentation would be that the extinction of certain species could affect the overall environment. For example, if numerous plant species became extinct, this would interfere with the oxygen rate in the air, because less photosynthesis would be taking place, but the same amount of cellular respiration will be occurring (Xu, et al., 2015). This is why there should be significant concerns with the potential effects of habitat fragmentation on genetic diversity.
Evidence
Climate change, such as a rise in overall global temperatures and increased toxins within the air, can be considered a distinct and defining issue that will not disappear without human prevention and intervention. Humans caused the original crisis that exists in rising greenhouse gases and the exhaustion of natural resources, and these impacts have only grown worse over time. Through the burning of fossil fuels, deforestation, creating areas of runoff or littering, everyday humans negatively impact the environment and the Earth, resulting in the destruction of several habitats and the extinction of species. The habitats that are being rapidly destroyed are sacred pieces of nourishment for all species and the survival of most species depends on the health of their habitat. In typical historical landscape structures, many species could roam freely across their environment and did not encounter reproduction or survival issues as rapidly as the typical habitat in today’s world. An example of a historical landscape being disrupted and altering the genetic diversity within an organism would be that of the Medicago falcata, another calcareous grassland plant, and the urbanization of the landscape around it. This caused the area of habitat patches to decrease, leading to the M. falcata, population to decrease, which ultimately resulted in low gene flow and a disrupted genetic diversity that prevented the ability to adapt to the new environment (Reisch et al., 2017). This destruction of the original habitat structure is destroying the genetic diversity not only within the current generation of species but changing the entire genetic blueprint for generations to come. These changes in the genetic diversity can range from mutations, point or chromosomal, or an increase of inbreeding, which results in lower gene flow and survival rate. Humans are directly attacking these species’ genetic diversity and survival by interfering within natural habitats, creating isolation by urbanization and deforestation, and ultimately causing irreversible damage to the environment. Habitats have become fragmented due to climate change and human intervention, which will ultimately lead to long-lasting negative effects on all species populations.
Genetic diversity has a distinct purpose that is present within every species, to create a variability that allows for further evolution and adaptation. This variability allows for the offspring to develop new traits or genes as a method for coping with potential problems that the parental generation faced. One example could be that clams developed certain coloring patterns based on the need to camouflage from the predators, as well as to better blend into their environment (Winkler, et al., 2001). This new trait may be a result of mutation or an adaptation from the parental generation caused by the stressors of the environment. These stressors can often include a lack of food, a rise in water temperatures, or the presence of a new predator resulting in a gradual change in the genetics of the subsequent generations thus increasing their fitness in the new environment (Winkler, et al., 2001). When a species is lacking genetic diversity, they become increasingly more vulnerable and have a higher potential for extinction, as they are not changing, creating variability within their genes through the process of meiosis, occurring during fertilization, which could cause one virus that targets a specific gene the ability to wipe out an entire population (Stanton, et al., 2009). An example of a species that has faced extinction due to habitat fragmentation would be that of the Spinx Macaw, which faced extinction after there was deforestation in Brazil and the species of tree that was vital to the bird’s survival was destroyed, leaving the habitat fragmented, and the S. Macaw extinct (Ruiz, 2020). This idea of genetic diversity is not only exclusive to animals within the animal kingdom, but humans as well. Variability is present in humans in several different aspects, one major aspect being that of hair color, which could have potential advantages or disadvantages based on environmental adaptation. The genetic diversity within these species, whether it is the S. Macaw or humans, can be spotted through different indicators, which could be the allelic richness, number of effective alleles, and expected heterozygosity (Gómez-Fernández, et al., 2016). These indicators are present in all species regardless of the environment in which they live, whether it is considered terrestrial or aquatic.
As stated above, habitat fragmentation can be a major threat to the genetic diversity of all species, causing irreversible damage and vulnerability. Habitat fragmentation directly affects species by causing inbreeding and an overall decrease in the species’ fitness for survival (Stanton et al., 2009). While some of these assumptions are true for most species, they cannot be fully applied to all species that may experience a change within their genetic diversity. It can be assumed that most populations of rare species are more affected by genetic factors before they are affected by habitat factors. By having these assumptions about all species, it can lead to inaccurate information being displayed about genetic diversity and the relationship between habitats and not provide the best strategy to save the genetic diversity of a species (Severns, et al., 2011). It is important to consider that several causes could affect the genetic diversity of a species, and no single solution will secure all species, but the habitat that a species lives in will play a major role in the fitness for survival.
The impacts of habitat fragmentation on species, in general, can be expanded beyond the idea of genetic diversity, but also be applied to the basic ideas of survival. When a habitat is disrupted, this will disrupt that species ability to find food, protection from weather and predators, and the opportunity to breed and reproduce. When the habitat is broken apart and separated, it will ultimately separate the species that live within the habitat, creating isolation and decreased population sizes. Habitats are the backbones of survival; they provide everything a species needs to survive, whether it is a type of food source, climate, or ability to hide from predators. When the backbone becomes affected, it will result in a chain reaction that leads to the destruction of all of the ecosystems within that habitat, ultimately causing environmental and global damage and the vulnerability of thousands of species that are all a vital part of the existence of humans (Mathias, et al., 2020). An example of this interconnectivity is from pollinators, such as bees. The effects from the loss of bees could result in pollen limitation, which would prevent various plants from being pollinated that is needed to survive. The loss of bees will result in a downwards spiral that could also destroy several plant species (Mathias et al., 2020). All species are interconnected, specifically through a vast food web that expands from producers to consumers, covers all organisms, including bacteria and fungi. When one species is affected, regardless of the species is considered to be predator or prey, this will lead to a chain reaction, as the transfer of energy and the cycling of nutrients will be affected throughout the entire web. For example, if a primary producer diminishes then there could be a decline in primary consumers due to heavy reliance on it as a food source and this could cause a disruption further up on the food web if species fail to adapt. This pattern could cycle through the entire food web, affecting every member of the food web. The importance of genetic diversity is that it has an impact on every single species, regardless if that species is the one that is being directly affected.
The direct effects of habitat fragmentation on genetic diversity are endless. Affecting the genetic build-up and structure of the DNA has the potential to affect all aspects of a particular species. The immediate effects of habitat fragmentation on species, in general, are isolation and a lowered ability to find food, as well as fewer potential breeding mates. The isolation that occurs from habitat fragmentation leads to lower genetic flow between the species, which causes a depletion of the genetic diversity that is seen within all species (Gómez-Fernández et al., 2016). When the isolation occurs, this can also lead to inbreeding, as there are fewer mates available, and inbreeding damages the adaptations that have already occurred within a species, making that species unable to generate alleles that allow for adaptation and evolution. Habitat fragmentation has a direct negative correlation with the genetic diversity of all species, and this fragmentation can result in a decreased amount of fitness, and landscapes that are severely fragmented support smaller populations at a lower density, leading to massive destruction through reduced gene flow (Stanton, et al., 2009). This genetic diversity is directly correlated with being affected by the habitat and the fragmentation or loss of said habitats. Multiple organisms have documented proof of being changed by habitat loss and that the fragmentation disrupts gene flow, preventing adaptation and evolution.
There are several examples of specific organisms that have been identified as having habitat fragmentation play a role in their genetic diversity. The first example is of the Dendrolimus punctatus, which is a plant species that shows fragmentation decreases the connectivity between two populations, which will create isolation, limit gene flow, and diminish a once-prominent genetic diversity (Zhou, et al., 2019). Another example of a species that has been affected by genetic diversity is the H. hermathena, a butterfly species in Brazil that has experienced dramatic habitat change, which resulted in reduced genetic health, ultimately damaging the rare alleles that were once present in this species (Massardo et al., 2020). A final example that explains the connection between habitat fragmentation and genetic diversity is of Cercis canadenis, a type of tree, which has a high level of genetic diversity, despite the habitat fragmentation that it is exposed to. These trees are still considered to have high genetic diversity, although forest fragmentation cannot be ruled out as an effect on the population, as well as specific disruptions in certain populations of trees (Ony, et al., 2020). While all of these species have had an affected genetic diversity that may not always be directly linked back to habitat fragmentation, all of these studies show that fragmentation could play a major role in the survival and adaptation of the species and needs to be monitored and protected.
There are several different types of habitat fragmentation, ranging in a variety of sizes, all having different effects on genetic diversity. While there is no definitive direct causal relationship between the habitat fragmentation size and genetic diversity, there are significant effects of the results of isolation on genetic diversity, which can lead to long term effects on population viability and adaption potential (Gómez-Fernández et al., 2016). It can also be determined that historical landscape structure can have an effect on how the genetic diversity within a species develops, and when there is a disruption in gene flow that is present for thousands of years, it can result in a decrease of plant populations and inbreeding, ultimately destroying the genetic diversity (Reisch et al., 2017). While there are several ideas about the causes of genetic diversity depletion and what genetic diversity entails, all ideas can be related to one universal element: habitat fragmentation. This shows that habitat fragmentation will affect the genetic diversity of a species negatively.
To prevent further destruction of genetic diversity and the disruption of gene flow and inbreeding, there must be preventative measures put into place, including habitat protection and the prevention of further fragmentation. Various protection acts could be enacted to focus on limiting human emissions, deforestation, and preventing any destruction of land that is home to an at-risk population. Other preventative measures that could occur include placing habitats under non – developmental zones to potentially reverse habitat fragmentation and, building corridors to allow the organism’s freedom to move from one habitat to another, thus enabling gene flow. If human emissions are better managed and regulated, then it could allow for less burning of fossil fuels and begin the process of reversing the present climate change. The United Nations has addressed the magnitude of the issue that climate change presents and reports an exponential growth of greenhouse gas emissions and other environmental factors that is leading to a rise in temperature, as well as changing the structure of all habitats (UN General Assembly, 2020). Protection of habitats could be creating safe havens of non-building zones, to protect specific species and their precious genetics, or it could be limiting the number of trees that a location can cut down in a specific period. Prevention of habitat fragmentation could be limiting the number of roads built, houses constructed, and overall location of communities, but species rely on habitats to adapt, evolve, and survive through the reversal of habitat fragmentation, which can be done through processes of creating areas where construction is allowed, and places where it is not allowed. The overall population could also do their part by reducing the number of fossil fuels used and switch to more reusable practices, such as limiting the amount of trash one throws into a landfill, littering, and building in areas where there are plenty of structures that have already been built to use. If each member of the population does their part in protecting habitats and preventing extensive damage, then the genetic diversity of all species affected could be restored and reverse many negative effects. Species will only continue to adapt and evolve as long as the government and the population are willing to work together and protect these valuable habitats and ecosystems.
Conclusion
In conclusion, habitat fragmentation has tremendous effects on many different species. Perhaps the most detrimental way being the effect on genetic diversity and the ability to adapt and evolve for continued survival. When habitat separation and isolation occurs, the result will hurt a species genetically, forcing them to inbreed, limit their gene pool, and lose the adaptive potential that has been continuously built upon for generations. Habitats allow for the genetic diversity to evolve within each species, creating variability in the species that makes it harder for the species to become vulnerable or extinct. Genetic diversity is vital to species adaption, evolution, and survivorship and damage could be detrimental to a species. To further prevent any damage to a species genetic makeup, habitat fragmentation must be prevented, and all habitats must be preserved to protect the species that are present, especially those considered to be at-risk species populations. Habitats are being fragmented every day and to reverse the negative effects of this fragmentation, we must begin to preserve the habitats and begin to put habitats back together. Whether it is in the form of replanting trees, plants or introducing species back into their natural habitat, these steps are vital in ensuring the creation of a better environment, and the ability to further evolve and adapt. Habitat fragmentation and genetic diversity are not exclusive to only the animal kingdom, but all living organisms in both terrestrial and aquatic ecosystems and this must be prevented for all organisms that call Earth their home.
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