5.5: Threats to Biodiversity

Invasive Species

An invasive species is a non-native organism that spreads rapidly and harms native species or ecosystems. Invasive species may compete with native organisms for resources, prey on native species, introduce diseases, or alter habitats. For example, the accidental introduction of the brown tree snake (Boiga irregularis) to Guam after World War II caused severe declines in native wildlife (figure \(\PageIndex{b}\)). The snake preyed on birds, lizards, and other small animals, leading to the local extinction of many native species and dramatically altering the island's ecosystem. Today, the brown tree snake remains one of the world's most damaging invasive species.

Pollution

Pollution can harm ecosystems and reduce biodiversity (figure \(\PageIndex{c}\)). Common examples include:

• Plastic pollution in oceans
• Pesticides that harm pollinators
• Excess nutrients that create algal blooms
• Toxic chemicals that accumulate in food webs

Pollution can directly kill organisms, reduce reproduction and survival, or degrade habitat quality. For example, excess fertilizer runoff can trigger algal blooms that remove oxygen from the water, making it difficult for fish and other aquatic organisms to survive. Plastic pollution can injure or kill wildlife through entanglement or ingestion, while pesticides can unintentionally harm beneficial insects such as bees and butterflies. Because pollution affects both individual species and entire ecosystems, it is a major contributor to biodiversity loss worldwide.

In Southern California, urban runoff can carry fertilizers, pesticides, oil, trash, and other pollutants into rivers, wetlands, and coastal ecosystems, affecting biodiversity and ecosystem health.

Human Population Growth

Human population growth and increasing resource consumption drive many of the threats to biodiversity. As the human population grows, more land, water, energy, food, and natural resources are needed to support human activities. Forests may be cleared for agriculture and housing, more resources are harvested from ecosystems, pollutants are released into the environment, and greenhouse gas emissions increase. As a result, habitat loss, overharvesting, pollution, invasive species, and climate change are all closely linked to the growing demand for resources. Sustainable resource use and conservation efforts can help reduce these pressures while supporting both human well-being and biodiversity.

Climate Change

Human-caused (anthropogenic) climate change is altering temperatures, precipitation patterns, sea levels, and ecosystem conditions worldwide. As environmental conditions change rapidly, some species may be unable to adapt or move to suitable habitat quickly enough (figure \(\PageIndex{d}\)). Climate change can also increase the effects of other threats such as habitat loss, invasive species, and disease.

Overharvesting

Overharvesting occurs when organisms are removed from the environment faster than populations can recover.

Examples include:

• Overfishing of commercial fish species
• Hunting wildlife for bushmeat
• Excessive logging of forests]
• Collecting medicinal plants faster than they can regrow

Overharvesting can reduce populations, disrupt ecosystems, and increase the risk of extinction.

Summary

Most biodiversity loss today is caused by human activities. The major threats can be summarized using the acronym HIPPCO: habitat loss, invasive species, population growth, pollution, climate change, and overharvesting. Understanding these threats helps scientists, policymakers, and communities develop effective conservation strategies. By protecting habitats, reducing overharvesting, controlling invasive species, reducing pollution, addressing climate change, and using resources sustainably, people can help conserve biodiversity and support healthy ecosystems.

Attribution

This page was heavily revised and rewritten by Erin Rempala and contains adapted content originally authored by Openstax and is licensed CC BY-NC-SA 4.0.