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Module 7: Biodiversity — Comprehensive Notes

Module 7 Notes: Biodiversity

  • Definitions and overall framing

    • Biodiversity encompasses variation at multiple levels and scales, not just the number of species.
    • Three major types discussed: landscape biodiversity, community biodiversity, and genetic biodiversity.
    • Biodiversity supports ecosystem services, resilience to disturbance, and human well-being.
    • We often hear “biodiversity = number of species,” but that only captures one aspect (species richness) within community biodiversity.

  • Landscape biodiversity

    • Looking at variation in species across space due to landscape features and topography.
    • Factors shaping landscape biodiversity: topography, elevation, climate, precipitation gradients, and how these influence plant communities.
    • Examples of high landscape biodiversity: mountains (varying elevations), tropical rainforest, coral reefs; relatively lower landscape biodiversity in large, homogeneous open oceans or sand/water systems.
    • Mountain ranges: high landscape biodiversity due to diverse microclimates and habitats.
    • Tropical rainforest: high landscape biodiversity with many microhabitats.
    • Coral reefs: high landscape biodiversity in a complex three‑dimensional habitat.
    • Open ocean: relatively low landscape biodiversity (less structural variation).
    • Grasslands of Kansas: relatively low landscape biodiversity.

  • Community biodiversity

    • Focuses on species richness (the number of species in an area) and relative abundance (evenness).
    • Richness vs evenness:
    • Species richness is the count of distinct species in an area.
    • Relative abundance (evenness) considers how evenly individuals are distributed among species.
    • Example with two fields:
    • Field A (left): four species present, but one dominates (mostly white butterflies) and others are represented by only one individual.
    • Field B (right): four species present with equal representation (e.g., three individuals per species).
    • Merely counting species (richness) would suggest similar biodiversity, but Field B has higher evenness and likely more equivalents in ecosystem function.
    • Implications: evenness reveals functional redundancy and stabilizes ecosystem processes; Field A may have a single dominant role and be more vulnerable to disturbances.
    • Summary for community biodiversity:
    • Needs both richness and evenness to understand true diversity and ecosystem functioning.

  • Genetic biodiversity

    • Variation in alleles and gene variants within a population.
    • High genetic biodiversity is critical for resilience to environmental change, disease, and new stresses.
    • Inbreeding depression: when genetic diversity is low, recessive deleterious alleles become more expressed, reducing fitness.
    • Examples and implications:
    • Agricultural crops with low genetic diversity are highly vulnerable to novel pests, diseases, and climate shifts (e.g., domesticated bananas).
    • Florida panther has very low genetic diversity due to bottlenecks from habitat loss and overhunting; hybridizing with the Texas puma is used to increase genetic variation.
    • African cheetahs exhibit low genetic diversity and various abnormalities, illustrating risks of reduced genetic variation.
    • Benefits of high genetic biodiversity:
    • Enables some individuals to tolerate extreme temperatures or novel pathogens, preserving population viability.
    • Provides a reservoir for future breeding, domestication, and medical discoveries.
    • Practical note: maintaining genetic diversity in wild populations supports ecosystem function and provides backups for domesticated crops and animals.

  • Why biodiversity matters

    • Biodiversity underpins ecosystem resilience to disturbances and environmental change.
    • Functional redundancy across species can prevent system collapse when some species are lost.
    • Genetic diversity enhances resistance to disease outbreaks, pests, and climate fluctuations.
    • Economic and human health relevance: biodiversity underwrites ecosystem services (soil regeneration, nutrient cycling, storm buffering, carbon sequestration) and medical discoveries.
    • Example of ecosystem services:
    • Wetlands: more biodiverse wetlands better at storm buffering than degraded, lower biodiversity wetlands.
    • Biodiversity supports production of goods (food, fuel, fiber, medicine) and ecotourism, biotechnology, and research.
    • Aesthetic, cultural, and spiritual values also contribute to why biodiversity matters.

  • Patterns of biodiversity and drivers

    • General patterns:
    • Higher biodiversity near the equator.
    • Higher biodiversity where plant biomass and productivity are high (lots of niches).
    • More habitat variation and environmental gradients promote more species.
    • Four factors predicting higher biodiversity: net primary production, disturbance regime, habitat gradients, and ecosystem complexity.
    • Net primary production (NPP): related to the amount of plant biomass and photosynthetic activity.
    • Disturbance: moderate disturbance can boost biodiversity; very high disturbance reduces it.
    • Habitat gradients: elevation, soil type, moisture, pH create diverse niches.
    • Ecosystem complexity: more interactions among organisms create more niches and specialization.
    • Comparing rainforest vs. grassland:
    • Rainforest: higher NPP and biomass, more habitat gradients, and higher ecosystem complexity → higher biodiversity.
    • Grassland: lower biomass, fewer habitats, simpler food web → lower biodiversity.

  • Biodiversity hotspots and conservation prioritization

    • Biodiversity hotspots: areas with a large number of endemic, native, or restricted species.
    • Purpose: prioritize conservation with the goal of achieving significant biodiversity preservation efficiently.
    • Examples and organizations:
    • Amazon rainforest as a flagship hotspot.
    • Biodiversity Hotspots mapped by Conservation International and other NGOs.
    • Pros of hotspot focus:
    • High biodiversity yield for conservation effort; clearer goals and public engagement; visually striking and engaging sites.
    • Cons / criticisms:
    • Can overlook less showy but ecologically critical areas (wetlands, semi-arid zones, deserts, less species-dense areas that support ecosystem services).
    • Ecosystems are interconnected; loss in hotspots can affect non-hotspot areas due to resource flows and ecological linkages.
    • International and country-level perspectives:
    • Hotspots are concentrated in tropical and subtropical regions; some systems (e.g., Southeast US) can be biodiverse but may receive less attention as hotspots.
    • Factors influencing hotspot identification and management:
    • Habitat availability and heterogeneity, ecosystem services provided, and connectivity to other habitats.

  • Threats driving biodiversity decline (drivers)

    • Global context: current extinction rates are vastly higher than background rates; evidence supports a sixth mass extinction driven by humans.
    • Key drivers (as discussed in the module):
    • Habitat loss and habitat fragmentation: destruction and division of habitats reduce resources and increase edge effects; example species affected include many birds in the longleaf pine ecosystem (red cockaded woodpecker, gopher tortoise, Bachman’s sparrow).
      • Notable statistics: habitat loss/endangerment is a major contributor to endangered bird species (e.g., 82% of endangered birds are endangered due to habitat loss).
      • Habitat fragmentation creates island-like populations and edge effects, reducing gene flow and increasing extinction risk.
    • Overharvesting: harvesting beyond populations’ replenishment rates; affects many taxa (fish, elephants, rhinos, sea turtles, etc.). Large-bodied, slow-reproducing species and migratory or schooling species are particularly vulnerable (e.g., cod collapse, bluefin tuna, Nassau grouper).
      • Overharvesting can lead to rapid population declines and local extinctions, especially when complemented by habitat loss.
    • Invasive (non-native) species: escaped and established, outcompete natives, alter ecosystems, and reduce native biodiversity.
    • Pollution: air and water pollutants, heavy metals, organics (DDT), microplastics, endocrine disruptors; pollutants can bioaccumulate and biomagnify through food webs; indicator species like lichens reveal air quality issues.
      • Bioaccumulation: toxins accumulate in an organism's tissues (e.g., fat) over time.
      • Biomagnification: toxins become more concentrated at higher trophic levels as predators consume contaminated prey.
      • Example pathway: algae contaminated with a toxin → small fish → larger fish → birds of prey; each step concentrates the toxin further.
      • DDT cited as a classic example; mercury and lead are other concerns.
    • Disturbance regime changes: altered frequency/intensity of floods, fires, storms; changes to riparian zones and wetlands affect their biodiversity and flood mitigation roles.
    • Climate change: overarching driver that interacts with all others; shifts in biomes, precipitation patterns, sea-level rise, ocean warming, coral bleaching, and ocean acidification threaten biodiversity across ecosystems.
      • Climate change interacts with habitat loss, pollution, invasive species, and disease to magnify biodiversity loss.

  • Evidence and case examples

    • Florida panther: bottleneck with low genetic diversity leading to reproductive and structural issues; cross-breeding with the Texas puma used to boost genetic diversity.
    • African cheetahs: low genetic diversity and associated health issues; conservation notes the need for maintaining genetic reservoirs.
    • Bananas: domestication reduced genetic diversity; wild relatives contain useful traits and potential backups for disease resistance, but many wild relatives are threatened by habitat loss and overharvesting.
    • Pacific Yew and Taxol: a plant-derived anticancer drug discovered through ecological sampling and subsequent lab work; demonstrates how biodiversity can contribute to medicine.
    • Nassau grouper: spawning aggregations are vulnerable to overharvesting; illustrates how life history traits interact with exploitation pressure.

  • Biodiversity conservation strategies and policies

    • Habitat protection and management
    • Protecting habitats and maintaining habitat quality to support resident and migratory species.
    • Managing for natural cycles (fire regimes, hydrology) to sustain ecosystem processes.
    • Recognizing that protected areas can become islands; the need for buffers and connectivity.
    • Protected areas and land management
    • National parks and wilderness areas provide large-scale preservation and coexistence of human use and biodiversity.
    • Yellowstone, Grand Teton, and similar reserves illustrate connectivity and corridor planning needs to avoid island effects.
    • Legislation and international frameworks (U.S. and global)
    • Endangered Species Act (ESA): protects imperiled species from extinction as a result of economic growth and development; enforcement by FWS and NOAA.
    • Lacey Act: prohibits trade in wildlife, fish, and plants taken illegally; evolution of enforcement agencies.
    • CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): international framework to regulate trade in endangered species; effectiveness depends on enforcement; some success (e.g., wildlife populations increased by about 66\% after species inclusion over more than twenty years).
    • International whaling moratorium: multi-country agreement to stop commercial whaling with limited exemptions; some countries have withdrawn or continued certain practices.
    • Private lands and incentive-based conservation
    • Green space zoning and planning policies to protect biodiversity on private lands.
    • Tax exemptions, conservation easements, and land trusts to prevent development and preserve habitat.
    • Economic incentives and conservation strategies
    • Ecotourism: using biodiversity as an economic asset to fund conservation; risk of over-visitation leading to habitat degradation and island effects if not properly managed.
    • Debt-for-nature swaps: international debt relief in exchange for conservation commitments in developing countries.
    • Habitat corridors and connectivity
    • Hedgerows and wildlife corridors (e.g., wildlife bridges and tunnels) to connect habitats across roads and urbanized areas.
    • Corridor design should reflect animal movement patterns and habitat requirements; ensuring adequate width and appropriate habitat features to minimize predation risk and funneling effects.
    • Buffer zones around protected areas mitigate edge effects and maintain functional habitat extent.
    • Umbrella species and habitat-based protection
    • Umbrella species (e.g., jaguar) protect large, intact habitats; protecting these species helps conserve many co-occurring and less charismatic species.
    • Species-specific and practical management
    • Captive breeding and reintroduction for iconic or at-risk species (e.g., whooping cranes, California conure); success depends on habitat quality, disease risk, and proper imprinting to avoid maladaptive behaviors.
    • Recovery efforts are challenging and depend on disease, predators, and available habitat; large, stable populations are easier to recover than very small ones.
    • Ethical and philosophical considerations
    • Debates about whether actions like hybridization (e.g., Florida panther x Texas puma) truly save a species or alter its identity.
    • Balancing human needs and biodiversity protection; prioritization strategies (hotspots vs. holistic landscape approaches) involve value judgments about which ecosystems to protect and how to allocate limited resources.

  • Indicators, monitoring, and science communication

    • Indicator species (e.g., lichens) reveal ecosystem health, particularly air and water quality.
    • Pollution can disseminate through air and water networks; pollutants like microplastics, DDT, mercury can bioaccumulate and biomagnify.
    • Monitoring biodiversity requires integrating landscape, community, and genetic data to capture comprehensive health of ecosystems.
    • Public engagement and education: biodiversity conservation benefits from communicating the value of ecosystems and the services they provide; hotspots can be powerful outreach tools but should not obscure the importance of less flashy areas.

  • Quick reference: key numerical and statistical notes

    • Endangered birds and habitat loss: 82\% of endangered bird species are endangered due to habitat loss alone.
    • North American forests: 95\% of deciduous forests have been lost or heavily altered.
    • Prairie remnants: only about 3\% of U.S. mixed and tallgrass prairies remain.
    • Biodiversity trends under CITES: wildlife populations increased by about 66\% after species inclusion over ~20 years, where enforcement is robust.
    • Extinction rates: current collective extinction rate is ~100\times faster than the background rate in geologic time.
    • Sixth mass extinction: ongoing, driven largely by human activities (habitat loss, overharvesting, invasive species, pollution, climate change).

  • Selected mechanisms and concepts to remember (with formulas where helpful)

    • Species richness and evenness (community biodiversity):
    • Let the field have species counts ni for each species i, with total N = \sumi n_i.
    • Proportions: pi = \frac{ni}{N}.
    • A common diversity measure is the Shannon index: H' = -\sumi pi \ln p_i, and evenness can be summarized as E = \frac{H'}{\ln S} where S is the number of species (richness).
    • Net primary production (NPP): a basic balance in primary production and respiration, often summarized as NPP = GPP - R where GPP is gross primary production and R is respiration.
    • Biomagnification of contaminants (illustrative path with DDT):
    • Let Ci be contaminant concentration at trophic level i, and let BMFi be the biomagnification factor from level i−1 to i.
    • Then, Ci = BMFi \cdot C{i-1}, and overall, Ci = C0 \prod{j=1}^{i} BMF_j for a path from base to level i.
    • Genetic diversity and populations:
    • Bottlenecks reduce genetic variation, increasing susceptibility to disease and maladaptation.
    • Hybridization can reintroduce genetic variation where appropriate, though it must be carefully evaluated for conservation goals.

  • Takeaways for exams and concept mastery

    • Distinguish landscape, community, and genetic biodiversity and understand how each contributes to ecosystem functioning.
    • Recognize why evenness (relative abundance) matters alongside richness for assessing biodiversity health.
    • Understand major drivers of biodiversity loss and why climate change is a cross-cutting threat.
    • Be able to explain conservation approaches (protected areas, corridors, umbrella species, habitat management, private lands strategies, international laws) and their practical challenges.
    • Be able to discuss the concept of biodiversity hotspots, including benefits and limitations.
    • Recall key case examples (Florida panther bottleneck, cheetahs, Nassau grouper, Pacific Yew Taxol) and their relevance to biodiversity and conservation.
    • Understand the role of indicator species and biomagnification in monitoring ecosystem health.
    • Appreciate the ethical and socio-economic dimensions of biodiversity conservation (ecotourism, debt-for-nature swaps, private land incentives).

  • Videos and further exploration

    • Video 1 (mass extinctions): focus on drivers of biodiversity loss and mass extinction context; recommended segments around 03:30–07:30 for core content.
    • Video 2 (Leopold and the Population Bomb connections): connects classic conservation ideas to historical context and policy implications.
    • Additional resources: links to wildlife corridors, hedgerows, wildlife bridges, and Central Park as contrasting examples of habitat connectivity and isolation.

  • Final note

    • Biodiversity is in rapid decline globally, but strategic conservation actions—when grounded in ecological principles and implemented with attention to landscape-scale connectivity and human dimensions—can bolster ecosystem services and resilience for future generations.