Anthropogenic Impacts On Biodiversity Biology Essay


Is the current rapid decline in the variety of life on Earth, largely attributed to the effects of human culture. In my essay I'm going to give a broad overview of the plight biodiversity is facing currently & mitigate the issues that need to be addressed. Biodiversity can be found at 3 varying levels: genetic diversity, species diversity & ecosystem diversity. Interactions between the 3 are vital to human welfare. Major threats facing biodiversity are; habitat destruction, introduced species, over-exploitation & food chain disruptions. The proactive strategy adopted in preventing a declining population is detecting, analysing, diagnosing & halting population declines. Weighing conflicting demands is a vital conservation strategy in determining species survival.

Edges & corridors can strongly influence landscape biodiversity. Setting up protected areas is a challenge which faces conservation biologists. Nature reserves must play a functioning role in the landscapes. Restoration of degraded areas is an increasingly important conservation effort. The main objective of sustainable development is reorienting ecological research & challenging all of us to reassess our values. The future of the biosphere is dependent on how quickly we act to protect our biophilia.

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Habitat destruction.

Human alteration/interference of a species habitat is the dominant threat facing biodiversity throughout the biosphere. Massive destruction of habitats worldwide has been caused by agriculture, urban development, forestry, mining & environmental pollution. In addition to habitat destruction over large regions, many natural landscapes have been fragmented into smaller patches. (Mt. Hood National Forest in Wisconsin United States you can see "islands" of coniferous forest that were created when much of the original forest was cut for timber.) Forest fragmentation is steadily increasing at a rapid rate in tropical forests. Tropical rain forest losses around Veracruz, Mexico exceeded 85% during the 20 year span from 1967 to 1987. Deforestation continued to proceed up from the lowlands & by 2000, only 8% of the original forest remained. Campbell, N. & Reece, J.(2002)

Deforestation in most areas can be attributed to agriculture or logging. Habitat fragmentation in almost all the cases leads to species loss (of populations of Bornean Orangutans due to deforestation in the Kutai National Park in Indonesia.) Meijaard, E. et al (2010)

Prairies of North America are also a good example of species loss. Prairie covered about 800,000 ha of Southern Wisconsin when Europeans first arrived, but now occupies less than 0.1% of its original area. Plant diversity surveys of 54 Wisconsin prairie remnants were conducted in 1948-1954 & then repeated in 1987-1988. During the few decades between surveys, the prairie fragments lost between 8% & 60% of their plant species depending on fragment. Ricketts, T. (1999)

Fahrig, L. (2003) Habitat loss has large, consistently negative effects on biodiversity. The negative effects of habitat loss apply not only to direct measures of biodiversity such as species richness, population abundance and distribution and genetic diversity (Gibbs 2001), but also to indirect measures of biodiversity and factors affecting biodiversity. Model by Bascompte et al. (2002) predicts a negative effect of habitat loss on population growth rate. This is supported by Donovan & Flather (2002), who found that species showing declining trends in global abundance are more likely to occur in areas with high habitat loss than are species with increasing or stable trends. Habitat loss has been shown to reduce trophic chain length (Komonen et al. 2000), to alter species interactions (Taylor & Merriam 1995), and to reduce the number of specialist, large-bodied species (Gibbs & Stanton 2001). Habitat loss also negatively affects breeding success (Kurki et al. 2000), dispersal success (Bélisle et al. 2001, Pither & Taylor 1998, With & Crist 1995, With & King 1999), predation rate (Bergin et al. 2000, Hartley & Hunter 1998), and aspects of animal behaviour that affect foraging success rate (Mahan & Yahner 1999).

Indirect evidence of effects of habitat loss

Robinson et al. (1995) found that reproductive success of forest nesting bird species was positively correlated with percentage of forest cover, percentage of forest interior, and average patch size in a landscape. Boulinier et al.(2001) found effects of mean patch size on species richness, local extinction rate, and turnover rate of forest birds in 214 landscapes. Because mean patch size had a 0.94 correlation with forest amount in their study, this result most likely represents an effect of habitat amount. Patch isolation effects Bender et al. (2003) and Tischendorf et al. (2003) They found that the "buffer" measures, i.e., amount of habitat within a given buffer around the patch, were best. This suggests a strong effect of habitat amount on interpatch movement. It also suggests, again, that effects of patch isolation and landscape-scale habitat amount are equivalent. Patch size effects & Extinction threshold were also examined in the paper.

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Proposed solutions: examined to eradicate habitat loss was restoration of degraded sites. Huxel, G. & Hastings, A. (2008)

Results demonstrate that either restoring patches adjacent to occupied patches or reintroducing the species into restored patches increases the efficacy of the recovery effort. The former of these two scenarios reduced the amount of fragmentation as compared to the random scenario resulting in a six-fold increase in patch occupancy during early phase in restoration. Proper management plans for restoration can have significant effects on the efficacy of a species recovery. This is especially important when funds are limited & relatively few sites can be restored. Successful restoration/conservation of endangered species requires a regional plan. Movement corridors essential to link isolated patches. It's very important for species that have patchy distributions of habitat & experience local extinctions in these patches.

The designated riparian areas will determine the success of species to re-populate & survive. These species require habitats that are close enough for effective dispersal to take place between habitats. Movement corridors can promote dispersal & reduce inbreeding in declining populations. Corridors are especially important to species that migrate among different habitats seasonally. However corridors can be harmful, the confined areas can spread disease, especially among small populations.

According to the International Union for the Conservation of Nature & Natural Resources (IUCN) implicates destruction of physical habitat in 73% of the species designated extinct, endangered, vulnerable or rare. Campbell, N. & Reece, J.(2002)

Most studies directly focus on terrestrial ecosystems; but habitat loss in marine biodiversity is increasingly under threat, especially on continental coasts & coral reefs. About 93% of the Earth's coral reefs, are among the most species-rich aquatic communities, have been damaged by human activities. At the current rate of destruction, 40-50% of the reefs could be derelict in the next 30-40 years. About â…“ of the planet's marine fish species utilise coral reefs, which occupy only about 0.2% of the ocean floor. Hughes, T. (2008)

Introduced species Intentional/Accidental

Species adopted into a non-native country have had detrimental effects on native animals. They may have been introduced to restore a degraded area, because they have the genetic makeup to survive in harsh conditions, or may induce a symbiotic relationship between species. Sometimes called exotic species, introduced species are those that humans transport from the species' native locations to new geographic regions. (Zebra mussels populating in the United States have reproduced in vast numbers. They interfere with native communities by feeding on phyto-plankton, the mussels depress populations of zooplankton; & the clearer water admits more sunlight, increasing the growth of aquatic plants in shallow waters. Zebra mussels crowd out native mollusc species leading to local extinction.) Native species can't compete with the population size. Pimentel, D. et al.,(2000)

African honey bee released by accident in Brazil has spread from the south up into North America. It was meant to breed a variety that would produce more honey in the tropics than the standard Italian honey bee. The aggressive nature of the Africanised honey bee has lead them to drive out the established colonies of Italian bees. Goulson, D. (2003)

The ease of travel by ships & aeroplanes has accelerated the transplant of species, especially un-intentional introductions. Non native species introduced in the UK; Floating pennyworth blocks out light & reduces oxygen for other plants and animals. Japanese knotweed spreads quickly & can damage property. It's a fast growing weed that appears to have no natural enemies in Britain. The grey squirrel has spread widely, with a population now estimated at over 2 million. They cause damage to woodland, and are largely responsible for the falling numbers of red squirrels in England. They are stronger and more adaptable than the red squirrel and they carry the Squirrelpox virus, which is lethal to red squirrels. (9/12/10)

Caulerpa an alga was probably released as a result of someone dumping a home saltwater aquarium native to Caribbean waters, the California invader is a variety of the alga that has been domesticated & selectively bred as an aquarium alga for its vigour & resistance to disease & herbivores. An earlier invasion of the Mediterranean Sea by this super seaweed is displacing many of the native algae there, & the same thing could happen now along the Pacific coast of North America. Campbell, N. & Reece, J.(2002)

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The Golden Eagle Trust in Ireland where birds of prey were being reinstated back into the Donegal countryside. It has been successful but 10 protected birds of prey including three Red Kites, two White-tailed Eagles, a Golden Eagle, three Buzzards and a Peregrine Falcon have been confirmed poisoned in the Republic of Ireland. All of these were poisoned by ingesting meat baits laced with Alphachloralose. Although the use of poison on meat baits for the control of crows was banned in 2008, the use of meat baits to kill foxes is still permitted under current regulations (Protection of Animals Act 1965). This loophole has allowed the continued use of poison and continues to pose a huge threat to our native birds of prey. However, an amendment to the Wildlife Act which will outlaw all use of poison on meat baits is imminent. ""&HYPERLINK ""news_id=11HYPERLINK ""&HYPERLINK ""article=267 (4/12/10)


The only way to control non-native species is to monitor their effect on the environment. Restrictions imposed on bringing animals into the UK, you will need a licence to bring in most non-native animals. The animal import laws help to protect crops and native wildlife, prevent diseases and to stop the trade in endangered species.

Some animals are not allowed into the UK because of the danger to native wildlife. People who do not hold a licence must be prosecuted it's the only way we can monitor/protect our native species. If reintroduced species are struggling human intervention is necessary to determine the problem & counteract the effect. They can do this by trying to eliminate the threat or if the threat cannot be quarantined it must be contained in a specific location in order to minimise spread. We can see that trying to control one species growth (poison meat baits for foxes) can have negative impact on another species (eagle). These considerations have to be addressed or an alternative to stabilising the fox population must be implemented otherwise the re-establishment of the non-native species would be in vain. (waste of time & resources).


Generally refers to human utilisation of plants or animals at rates exceeding the ability of populations of those species to rebound (overhunting & overfishing of animals.) Especially susceptible to over exploitation are large species with low intrinsic reproductive rates, such as elephants, whales, rhinoceroses & other animals considered valuable by humans.

Several factors contribute to the overexploitation of large, tropical forest animals Millner-Guland et al. (2003). The weak economies of many tropical countries fail to provide sufficient jobs for their growing populations while land-use change, improved infrastructure, and new technology facilitate commercial hunting. Land-use change brings hunters and their markets closer to previously remote forests. Improved infrastructure provides access to forest interiors over roads opened for timber and mineral extraction as well as access to distant urban markets. The new technologies include guns, wire snares, battery-powered lights, and motorised transport and have largely replaced traditional hunting technologies even among indigenous peoples. Collectively, land-use change, improved infrastructure, and new technologies increase the return for time spent hunting and make it possible for hunters to deplete their prey to lower levels Wright, S. et al. (2007)

Species on small islands are particularly vulnerable (eg. in the 1840s humans had overhunted the great auk a large, flightless seabird to extinction on islands in the Atlantic Ocean because of a demand for feathers, eggs & meat.) Campbell, N. & Reece, J.(2002)

The decline of the African elephant, the largest extant terrestrial animal hunted to near extinction. African elephants take 10-11 years to reach sexual maturity, & then a fertile female has a single calf every 3 to 9 years. The potential rate of population ↑ is only about 6% per year, a low growth rate. Illegal hunting for ivory is the major cause of this collapse of elephant populations. Martin, A. (2008)

Overfishing has dramatically reduced the population sizes of many commercially important fish species. Many populations of fishes that humans consume have now been reduced to levels that cannot sustain further exploitation. Serious concerns have been raised about the ecological effects of industrialised fishing, spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels. However, a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities, relative to contemporary ones. Myers, R. & Worm, B. (2003)

The fate of the North Atlantic blue fin tuna for example is in jeopardy. For the past few decades this big tuna was considered a sport fish of little commercial value. Then, beginning in the 1980s wholesalers began air freighting fresh, iced blue fin to Japan for sushi & sashimi. With the demand & prices the stock was predictably depleted. It took 10 years for population to be less than 20% of its 1980 size. The demise of the northern cod fishery off Newfoundland in the 1990s shows how it is possible to over harvest what had been a very common species. Fromentin, JM. & Powers, J. (2005).


Even with the strict legislation of fish stock quotas there still continues to be exploitation due to expanding human population & demand made accessible by new harvesting technologies, such as long-line fishing & modern trawlers. Governments need to be stricter on imposing caps on what countries are allowed to fish in relation to demand & supply, and can only fish off their coast. Fines & prosecutions have to be inflicted or else we will drive these species toward extinction.

Disruption of Food Chains

Like falling dominoes, the extinction of one species can doom its predators. But this is only likely if the predator exclusively feeds on one species which is a rare trophic arrangement. According to the small-population approach, a population's small size can draw it into an extinction vortex.

The key factor driving the extinction vortex is the loss of the genetic variation on which a population depends for adaptive evolution. Both inbreeding & genetic drift can cause a loss of genetic variation, & both of these processes intensify as a population shrinks. Overhunting of northern elephant seals in the 1890s dropped the species to only 20 individuals - clearly a bottleneck with reduced genetic variation. Since that time, however, the northern seal populations have rebounded to about 150,000 individuals. Genetic variation in these populations remains relatively low. Hoelzel, A. et al. (1993)

In some cases, low genetic diversity is associated with population expansion rather than decline. These cases may stand out precisely because they are so unusual. Thus, conservation biologists have good reason to be concerned about very small populations with low genetic variation.


The only way to control the spread of this plant is to contain it. It's inevitable that it will dominate the area, so the only rational outcome is to prevent it from spreading. Our priority is protecting the vulnerable site. We must monitor & record the species that are vulnerable & are at threat of becoming extinct. They must be listed as an endangered species & anyone caught hunting them must be severely prosecuted. Limitations of hunting a single species should be imposed; we must allow species time to recover.

There are, interventions based on small population theory, including introducing genetic variation from one population to another. The declining - population approach is even more action orientated, focusing on threatened & endangered populations even if they are far greater than minimum viable size. The declining - population approach necessitates that population declines be gauged on a case by case basis, with researchers carefully dissecting the causes of a decline before recommending or trying corrective measures. Krebs, C. (2008)

If, for example, the biological magnification of a particular toxic pollutant is causing a decline in some top-level consumer such as a predatory bird, then only reduction or elimination of the poison in the environment can save that particular species. Rarely is the situation so straight forward, but there are procedures to help with even complex cases.

Conserving species involves weighing conflicting demands

It is necessary to weigh a species' biological & ecological needs against other conflicting demands. Conservation biology often focuses on the relationship between science, technology & society.

The ongoing & often bitter debate in the U.S. Pacific northwest pits saving habitat for populations of the northern spotted owl, timber wolf, grizzly bear & bull trout against demands for jobs in the timber, mining & other resource extraction industries. Campbell, N. & Reece, J.(2002)

Solution: If possible an alternative location should be researched, or examine if the species could be relocated to a different area.

Ecological role of the species is another factor we have to weigh in. Different species are competing for economic development & living space. Because we cannot save every endangered species, we must determine which ones are vital for conserving biodiversity as a whole. Species do not exert equal influence on community & ecosystem processes. Some organisms, called keystone species, have disproportionately large impacts relative to their numbers. Some keystone species significantly modify habitats, creating diverse patches that support numerous other species. Predators have also been labelled keystone when they control the densities of other types of ecologically significant prey species. Sea otters, a keystone predator in the North Pacific, were once relatively abundant. They were hunted to near extinction in the 18th & 19th centuries by European & Russian trappers.

Sea otters have often been referred to as keystone predators (e.g., Duggins 1980, Estes and Palmisano 1974) because they limit density of sea urchins, which in turn eat kelp and other fleshy macroalgae that form the basis of a different community than is present in their absence (VanBlaricom and Estes 1988). Thus, otter removal has community-level influences, by releasing from predation a primary consumer that eats a plant that harbours other organisms. Mills, L. et al. (1993).

Solution: If we abandon the keystone-species concept and the rigid structure it implements on species interactions, we fail in our efforts to protect biodiversity. A keystone is a species on which the persistence of a large number of other species in the ecosystem depends. If the keystone is eliminated the whole system collapses. Therefore necessary to protect the species on which everything else relies upon.

Conclusion: Many of the precautions taken to conserve biodiversity and promote its sustainable use have been successful in limiting biodiversity loss. Rates of loss are now lower than they would have been in the absence of such actions. Actions that focus primarily on conservation include: protected areas; species protection and recovery measures for threatened species; conservation of genetic diversity; both on and off sites (such as in gene banks); and ecosystem restoration. Actions that focus primarily on sustainable use include: providing economic incentives; incorporating biodiversity considerations into management practices (agriculture, forestry, and fisheries); ensuring that local communities benefit from biodiversity.

Reducing the threat of biodiversity has to be enforced globally from the top down. Governments need to be aware of what is happening to their countries and need to act to educate, make people more aware by communicating what their actions have on accelerating the crisis we are trying to contain. The preservation of our natural ecosystem is vital to our continued maintenance of the planet as we know it.