Conservation Biology and Human Impacts Lecture
Major Threats to Biodiversity and Human Impact
Human activities have historically impacted species and biodiversity in significant ways, predominantly resulting in adverse effects, although some impacts are context-dependent.
An example of complex impact is nutrient enrichment: while it may initially benefit a few specific species like photosynthesizers, it often leads to the creation of anoxic "dead zones" that are lethal to most other species in the ecosystem.
The "Big Four" major threats to biodiversity caused by human activity include: - Habitat Loss: The physical destruction or alteration of natural environments. - Introduced Species: Non-native species that can outcompete native species for resources. - Overharvesting: The excessive removal of individuals, such as overfishing, at rates faster than populations can recover. - Global Change: A broad category encompassing climate change, chemical toxins, and nutrient enrichment.
Landscape Transformation and Global Habitat Loss
Humans have been extremely successful as a species, surviving in nearly every ecosystem type across the planet.
This success has come at a massive cost to the environment; humans have converted, transformed, or altered over of the global landscape.
Global examples of landscape alteration: - Vietnam: Mountainous rainforests have been extensively cleared and converted to agriculture, except in the most inaccessible areas. - This pattern of transformation is global, impacting every continent and every ecosystem in some way, though some regions are more severely affected than others.
Conservation Priorities: Patches and Connectivity
Conservation biologists are increasingly focused on the dynamics of habitat patches, specifically patch size and connectivity.
Research is shifting toward protecting small, vulnerable populations that reside in fragmented patches.
Identifying critical habitats is essential because biodiversity is not spread evenly across the globe (e.g., the Arctic has significantly fewer species than a tropical rainforest).
These conservation challenges are rarely purely science-based; they often require difficult conversations regarding ethics, morality, and human values.
The Extinction Vortex and Genetic Diversity
Population size is a critical factor in species survival. If a population falls below a certain "tipping point," it can lead to extinction.
The Extinction Vortex: A phenomenon where a small population size leads to a downward spiral of declining health and numbers. - In a large population, individuals interbreed to maintain high genetic diversity. - In a small population, inbreeding occurs, where genetically similar individuals (relatives) mate.
The Biological Consequences of Inbreeding: - Lowers genetic diversity and leads to the homogenization of the gene pool. - Results in lower individual fitness, reduced ability to survive, and lower reproductive success. - Can manifest as birth defects and disease. - Historical Example: Charles Darwin married his cousin, and his children suffered from various diseases that are now understood as results of a genetic bottleneck or inbreeding.
The Vortex Feedback Loop: Small population $\rightarrow$ Inbreeding/Genetic Drift $\rightarrow$ Loss of Genetic Variability $\rightarrow$ Lower Fitness/High Mortality $\rightarrow$ Smaller Population. This process can happen rapidly over just a few generations.
Population Metrics: MVP and Effective Population Size
Total Population Size (): The raw number of individuals in a specific population (e.g., the number of students in a classroom).
Minimum Viable Population (MVP): The absolute minimum population size required for a species to be able to survive and avoid the extinction vortex.
The Importance of Genetic Diversity: Even if a population has a high , low genetic diversity makes it vulnerable. For example, a room of clones of one person would all be killed by a single disease that the original individual was susceptible to.
Effective Population Size (): This metric accounts for the number of individuals in a population that are actually capable of breeding, considering the ratio of males to females and their reproductive maturity. - Case Study: Freshwater mussels are long-lived filter feeders (living for decades). Some populations appear healthy because they contain many individuals, but they have not reproduced in , , or even years. These populations have a very low effective population size and face a high risk of sudden extinction as the aging individuals die off.
Socio-Economic Challenges in Conservation
Conservation decisions are rarely clear-cut and often involve conflicting demands between environmental protection and human economic needs.
Examples of conflicting demands: - A proposed development might impact the limited habitat of a threatened insect species but provide essential jobs for an economically struggling community. - In the Western United States, there is a conflict between preserving habitat for species and the traditional use of land for livestock grazing. - Water rights in Arizona: Irrigating cotton crops uses water from the Colorado River, preventing the river from reaching the ocean and negatively impacting indigenous cultures downstream.
Stakeholders: Conservation involves negotiations between scientists, ranchers, business owners, and legislators to balance diverse viewpoints.
Landscape Structure and Edge Effects
Fragmentation: The process of breaking large, contiguous habitats into smaller, isolated patches.
Edges and Biodiversity: The boundary between two ecosystems (e.g., a river running through a forest) often creates unique conditions. - Some species, like deer, thrive at the edges of forests. - Stream insects benefit from carbon inputs like senescent leaf litter at the forest-river edge. - Areas with high edge-to-surface-area ratios can sometimes support more biodiversity than uniform, deep-forest blocks.
The Biological Dynamics of Forest Management Project (BDFMP)
This is a massive global initiative that originated from concerns over deforestation in the Brazilian rainforest.
Scientist-Legislator Collaboration: Researchers worked with lumber companies and the Brazilian government to study the effects of different cutting patterns.
Experimental Design: The project created an array of forest fragments of varying sizes (small vs. large) and distances (near vs. far) to determine if patches could sustain species after clear-cutting.
Finding: Fragmented patches have high conservation value, particularly if they are connected, as they allow mobile species like birds and dragonflies to move between patches and maintain genetic diversity.
Movement Corridors and Connectivity
Movement Corridors: Strips of habitat (e.g., a forest bridge over a highway or a narrow strip of wood connecting patches) that allow animals to move between isolated fragments.
Benefits: These corridors mitigate genetic bottlenecks and lower the risk of an extinction vortex for terrestrial mammals and other species that cannot fly.
Effectiveness: While expensive and initially avoided by some large mammals, many animals (including rodents and small mammals) use them immediately. Over time, larger animals can be "trained" or naturally learn to use these pathways depending on their placement.
Urban Ecology and Sustainable Development
Urban Ecology: A subdiscipline that examines organisms and their environment within urban settings to promote sustainable city development.
Practical Examples of Urban Ecology: - Salt Lake City: The creation of a "green belt" and a restored river park in the city center for both biodiversity and flood mitigation. - Halifax: The new public library features a rooftop grassland and garden, providing a coffee shop setting where people can experience biodiversity in the middle of a dense urban environment.
Society is trending toward more symbiotic relationships with nature, though the pace of development and permits often lags behind scientific solutions.
Biodiversity Hotspots
Heterogeneous Distribution: Biodiversity is not spread evenly across the Earth; it is concentrated in "hotspots."
Examples of Hotspots: - Freshwater networks and small streams often have a much higher density of species than surrounding land. - High Montane Lakes. - Tropical terrestrial and marine regions.
Economic Perspective: Because conservation funds are limited, biologists often prioritize these hotspots to get the "largest bang for our buck" in terms of species protected.
Global Change: Nutrients, Toxins, and Climate
Nutrient Enrichment: Fertilizers from agricultural lands (e.g., the Mississippi River Basin) drain into water bodies, causing nitrogen hotspots. High nitrogen feeds algae and microbes, which deplete oxygen, leading to dead zones for fish and other species.
Toxin Accumulation: - Pharmaceuticals: Medications (like estrogens from birth control) enter wastewater and cannot be fully removed by treatment plants. Downstream, this can lead to biased fish populations (e.g., all females). - Forever Chemicals: Substances that persist in the environment and accumulate in water bodies. - Plastics: Microplastics have been found in the tissues of shorebirds, coral reefs, and even human brains. In coral, plastic presence is linked to higher disease susceptibility.
Climate Change: - Mechanism: Sunlight enters the atmosphere and is normally reflected by snow/surfaces. Increased greenhouse gases (like ) create a shield that prevents radiation from reflecting back into space, causing warming. - Biological Impacts: Species are forced to move further north, south, or higher up mountain ranges. Eventually, they run out of habitat (e.g., reaching the rocky, soil-less peaks of mountains). - Ocean Acidification: Increasing levels are making the oceans more acidic, harming marine life.
Biophilia and the Future
The cumulative impact of human activity is described as "death by a thousand cuts."
Ecological Footprint: A per capita measure of human impact on the environment, typically higher in economically developed or developing countries.
Biophilia: A concept emphasizing the inherent connection between humans and the environment, advocating for a view of the natural world based on connection rather than exploitation or dominance.