13: Threats to Biodiversity

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Figure \(\PageIndex{1}\): The northern spotted owl (*Strix occidentalis caurina*) is a western North American owl species that prefers large swaths of pristine old growth forests (that typically take 150-200 years to mature) for nesting. Unfortunately, most western forests have been regularly harvested for timber since around the establishment of the Forest Service in 1905. Thus, this species preferred habitat has been largely destroyed and their populations have plummeted. Habitat destruction is the number one cause for species extinction globally. For some species that are very habitat specific, like the northern spotted owl, there are not as many conservation actions to choose from that can help reverse declining population trends.. Image by USFS (licensed under CC-BY 2.0)

Chapter Summary

The core threat to biodiversity on the planet is the combination of human population growth and the resources used by that population. The human population requires resources to survive and grow, and many of those resources are being removed unsustainably from the environment. The five main threats to biodiversity are habitat loss, pollution, overexploitation, invasive species, and climate change. Increased mobility and trade has resulted in the introduction of invasive species while the other threats are direct results of human population growth and resource use.

Learning Objectives

After reading this chapter you should be able to:

Explain causes of habitat loss and degradation.
Describe the effects of habitat fragmentation and the importance of corridors, and connectivity to conservation.
Explain how plastic pollution has become a huge environmental problem and why recycling has not been an effective solution.
Provide examples of invasive species and their ecological impacts.
Provide examples of species that are overexploited.
Explain why climate change is expected to accelerate biodiversity decline.

Attribution

13.1: Habitat Loss and Fragmentation
Habitat loss includes habitat destruction, altering the physical environment such that a species can no longer live there, and habitat fragmentation, which involves dividing a habitat into discontinuous patches.
13.2: Pollution
Pollution is the release of harmful chemicals or other materials into the environment. Some types of air pollution results in acid deposition and climate change. Nutrient pollution of water bodies due to fertilizer overuse results in eutrophication.
13.3: Invasive Species
Invasive species are those occurring outside of their historical distribution that cause ecological and/or economic harm. Invasive species can overpredate or outcompete native species, sometimes causing their extinction or extirpation. Examples of invasive species include the Asian carp, zebra mussels, Bd (which causes a fungal disease in amphibians), purple loosestrife, and the European starling. Biological control employs other organisms to control invasive species and has had successes and fa
13.4: Overexploitation
Overexploitation involves removing organisms at a faster rate than they can be replenished. Examples include the poaching of elephants, unsustainable hunting for bush meat, overfishing, and overcollection of slow-growing plants and fungi.
13.5: Climate Change
The release of greenhouse gases, like carbon dioxide and methane, when burning fossil fuels for energy causes climate change. Not only does climate change involve an increase in average global temperature, but it also results in unpredictable weather patterns. Climate change threatens biodiversity through a variety of mechanisms and can cause species range shifts, mismatched biotic interactions, sea level rise, and ocean acidification.