🌾World Biogeography Unit 9 – Human Impacts on Global Biodiversity

Key Concepts and Definitions

• Biodiversity encompasses the variety of life at all levels of organization, from genes to ecosystems
• Species richness measures the number of different species present in an area
• Ecosystem services are benefits humans derive from ecosystems (clean water, pollination, nutrient cycling)
• Anthropogenic activities are human actions that impact the environment
• Habitat fragmentation divides contiguous habitats into smaller, isolated patches
• Invasive species are non-native organisms that cause ecological or economic harm
• Extinction occurs when the last individual of a species dies
  • Local extinction happens in a specific area, while global extinction affects the entire planet

Historical Context of Biodiversity

• Earth has experienced five major mass extinction events in its history
• Human activities have accelerated the rate of species extinctions in the last few centuries
• The Holocene epoch, which began ~11,700 years ago, marks the start of significant human impacts on biodiversity
• Agricultural revolution (~10,000 years ago) led to land conversion and domestication of plants and animals
• Industrial revolution (late 18th century) increased resource exploitation and pollution
• Globalization has facilitated the spread of invasive species and diseases
• Current era is sometimes referred to as the Anthropocene due to the scale of human influence on Earth's systems

Major Human Activities Affecting Biodiversity

• Habitat loss and degradation due to land-use changes (deforestation, urbanization, agriculture)
• Overexploitation of resources through hunting, fishing, and harvesting
• Introduction of invasive species, both intentionally and accidentally
• Pollution of air, water, and soil with toxic substances and excess nutrients
• Climate change driven by greenhouse gas emissions
  • Alters temperature, precipitation patterns, and sea levels
• Human population growth and increasing resource consumption exacerbate these pressures
• Synergistic effects of multiple stressors can amplify impacts on biodiversity

Impacts on Terrestrial Ecosystems

• Deforestation has led to the loss of primary forests and their associated biodiversity
  • Tropical rainforests are particularly affected (Amazon, Congo Basin, Southeast Asia)
• Habitat fragmentation reduces connectivity and isolates populations
• Agricultural expansion has converted diverse habitats into monocultures
• Overgrazing by livestock can lead to soil erosion and desertification
• Urbanization destroys and fragments habitats, while also creating novel urban ecosystems
• Invasive species can outcompete native species and alter ecosystem functions
  • Examples include kudzu in the southeastern US and cane toads in Australia

Impacts on Aquatic Ecosystems

• Overfishing has depleted many fish stocks and disrupted marine food webs
  • Cod fisheries in the North Atlantic have collapsed due to overexploitation
• Pollution from agricultural runoff, industrial waste, and sewage degrades water quality
• Eutrophication caused by excess nutrients leads to algal blooms and oxygen depletion
• Dams and water diversions alter river flow and connectivity, affecting aquatic species
• Coastal development destroys wetlands, mangroves, and coral reefs
• Ocean acidification due to increased atmospheric CO2 threatens marine organisms with calcium carbonate shells or skeletons
• Invasive species can disrupt aquatic communities (zebra mussels in the Great Lakes)

Biodiversity Hotspots and Vulnerable Areas

• Biodiversity hotspots are regions with high species richness and endemism that face significant threats
  • Examples include the Tropical Andes, Madagascar, and the Caribbean Islands
• Island ecosystems are particularly vulnerable due to their isolation and unique species
• Montane ecosystems are sensitive to climate change as species have limited ability to shift ranges
• Coral reefs are biodiversity hotspots threatened by ocean acidification, warming, and pollution
• Wetlands, such as the Pantanal and the Sundarbans, are under pressure from land conversion and sea-level rise
• Arctic ecosystems are rapidly changing due to amplified warming at high latitudes

Conservation Strategies and Policies

• Protected areas, such as national parks and wildlife reserves, safeguard habitats and species
• International agreements, like the Convention on Biological Diversity, promote conservation and sustainable use
• Habitat restoration aims to recover degraded ecosystems and their functions
• Ex-situ conservation, such as seed banks and captive breeding programs, preserves species outside their natural habitats
• Community-based conservation engages local communities in conservation efforts
• Ecosystem-based management considers the interactions and services of entire ecosystems
• Reducing greenhouse gas emissions is crucial for mitigating climate change impacts on biodiversity

Future Outlook and Challenges

• The ongoing sixth mass extinction, driven by human activities, threatens global biodiversity
• Climate change will increasingly affect species distributions, phenology, and interactions
• Continued human population growth and resource demand will intensify pressures on ecosystems
• Balancing conservation with human needs, such as food security and economic development, is a major challenge
• Addressing the underlying drivers of biodiversity loss, such as unsustainable consumption patterns, is essential
• Protecting biodiversity requires a combination of local actions and global cooperation
• Ecosystem restoration and nature-based solutions can help mitigate and adapt to environmental changes
• Integrating biodiversity conservation into decision-making across sectors is crucial for sustainable development