Bio 180 Week 10: Species Interactions, Biodiversity, and Conservation

Species Interactions and Coevolutionary Dynamics

• Coevolutionary Arms Race: This refers to a repeating cycle of reciprocal adaptation between species. In this process, species are constantly adapting to one another to survive, directly influencing each other's evolution through successive changes and counter-changes.

• Parasitism: A symbiotic relationship where a parasite lives in or on a host, extracting resources at the host's expense.

  • Endoparasite: These organisms live inside the host and consume small amounts of tissue or nutrients. They are typically much smaller than the host. Their impact is usually not fatal over the long period they inhabit the host. An example includes tapeworms.

  • Ectoparasite: These organisms live on the exterior of a host, consuming small amounts of tissue or fluids (such as blood). Like endoparasites, they are small relative to the host and generally not fatal. An example includes ticks.

  • Parasitoid: These are free-living as adults but function as endoparasites or ectoparasites during their larval stage. They hatch from eggs laid on or inside a host and eventually consume the host entirely, which is always fatal to the host. Parasitoid wasps are a primary example.

• Parasite-Host Coevolution Case Study:

  • Roundworms and Ants: Roundworms lay eggs in the abdomen of an ant. This causes the ant's abdomen to swell and turn red, making it resemble a berry.

  • Transmission Pathway: Birds mistake the red ant for a berry and consume it. The roundworms then grow inside the bird and are eventually excreted through the bird's feces. Ants then consume the feces, restarting the cycle.

Understanding Biodiversity and Its Components

• Genetic Diversity: This is the total genetic information contained within all individuals of a specific group (population or species).

  • Increases: Mutations create new alleles, increasing genetic diversity.

  • Decreases: Natural selection, genetic drift, and gene flow can decrease genetic diversity.

• Species Richness: A count of how many different species are present in a specifically defined area.

  • Geographic Pattern: Species richness is generally highest in tropical regions and gradually declines toward the planetary poles.

• Species Diversity: This measure considers both richness (number of species) and evenness (the relative abundance of each species).

  • High Diversity: Indicated by high evenness among species.

  • Low Diversity: Indicated by low evenness, often where one species dominates the environment.

  • Evolutionary Impact: Speciation increases species diversity, while extinction decreases it.

• Phylogenetic Diversity: Measures the evolutionary distinctiveness of a community. Species are considered more diverse if they are phylogenetically distant from other species in the same community.

• Functional Diversity: Focuses on species with functional traits that play specific roles in ecosystem operations. Examples include:

  • Keystone Species: Species with a disproportionately large effect on their environment relative to their abundance.

  • Nitrogen Fixers: Organisms that convert atmospheric nitrogen into a usable form for plants.

• Ecosystem Diversity: A measure combining horizontal diversity (within a trophic level) and vertical diversity (across different trophic levels).

• Endemic Species: Species found in one particular geographic area and nowhere else on Earth.

• Biodiversity Hotspots: Regions identified as urgent priorities for conservation due to exceptionally high levels of biodiversity and significant threat of habitat loss.

Ecosystem Function, Productivity, and Stability

• Ecosystem Function: The sum of chemical and biological processes characteristic of a specific ecosystem. Key functions include:

  • Primary production.

  • Nitrogen cycling.

  • Decomposition.

  • Carbon storage.

• Formation: New ecosystems or functions form in response to changes in climate or physical conditions.

• Diversity Patterns: Biodiversity is higher on land than in the sea, largely because land areas with greater geographical variation provide more niches.

• Net Primary Productivity (NPP): This is the source of chemical energy utilized by all species in a food web.

  • Increasing species richness and functional diversity generally increases NPP.

  • Three Reasons for Increased NPP via Species Richness:

    1. Resource Use Efficiency: A diverse range of species uses resources more efficiently because they possess non-overlapping niches.

    2. Facilitation: Certain species improve the environment (e.g., providing nutrients or shade), making it more favorable for other species.

    3. Sampling Effect: Plots with high species richness are statistically more likely to include one or two high-productivity species that result in higher overall output than low-species plots.

• Biodiversity and Stability:

  • Resistance: The degree to which a community remains unchanged following a disturbance, maintaining productivity and function.

  • Resilience: The speed at which a community recovers its former levels of species richness or productivity after a disturbance.

Ecosystem Services and Human Ethics

• Ecosystem Services: Direct and indirect benefits humans receive from ecosystems.

  1. Provisioning Services: Raw materials such as food, fuel, fiber, medicine, and water. Includes bioprospecting, the exploration of organisms for new drugs or industrial ingredients.

  2. Regulating Services: Earth's life support systems, including climate moderation, soil formation, $O_2$ and $CO_2$ regulation, water purification, air cleaning, and waste decomposition.

  3. Supporting Services: Processes that enable other services, such as primary productivity, nutrient cycling, pollination, and pest control. These are often impossible for humans to replicate if lost.

  4. Cultural Services: Enhancements to the quality of life, including aesthetics, recreation, education, and spiritual value.

• Ethical Obligations: Humans are argued to have an ethical duty to preserve ecosystems because:

  1. Organisms possess intrinsic worth.

  2. Industrialized nations cause the most harm, while poor countries suffer most from the consequences.

  3. Future generations have a right to the ecosystem services currently available.

Global Threats to Biodiversity

• Current State: Species are vanishing at rates $100 \times$ to $1000 \times$ higher than the average background extinction rate.

• Taxonomic Vulnerability: Amphibians are currently the most endangered group of species.

• Primary Drivers of Decline:

  • Habitat Loss: The most significant factor for terrestrial species.

  • Overexploitation: The dominant problem for marine species.

  • Invasive Species and Pollution: Greater impact on freshwater ecosystems than terrestrial or marine.

  • Climate Change: Currently has a larger impact on marine species than freshwater or terrestrial ones.

• Habitat Destruction Specifics: Involves physical and functional loss through logging, burning forests, damming rivers, dredging wetlands, plowing prairies, grazing livestock, excavating fuels, and urbanization.

  • Less than 25% of Earth's land remains wild, mostly near the poles where biodiversity is lowest.

  • Primary Forests: Targeted for preservation because they possess high biodiversity from deep evolutionary history.

  • Tropical Feedback Loop: Loss of tropical forests reduces cloud formation and increases soil erosion, potentially transforming the area into a savanna.

Habitat Degradation and Fragmentation

• Habitat Fragmentation: The process of dividing large, contiguous habitats into small, isolated fragments.

  • Consequences: Small fragments cannot support top predators (e.g., apex predators), leading to trophic cascades that affect primary productivity, nutrient cycling, and susceptibility to fire or disease.

  • Isolation Risks: Specific vulnerabilities for small populations include:

    1. Stochastic Events: Catastrophic chance events like storms or disease outbreaks.

    2. Inbreeding Depression: Reduced genetic diversity caused by the random loss of alleles through genetic drift in the absence of gene flow.

• Edge Effect: Biomass declines sharply at the edges of fragments because the forest interior is more exposed to outside elements.

• Wildlife Corridors: Strips of undeveloped habitat (e.g., overpasses or underpasses) that connect preserved areas, facilitating movement, recolonization, and gene flow.

Pollution, Overexploitation, and Invasive Species

• Overexploitation: Any unsustainable removal of organisms from the environment for human use. This is most prevalent in marine environments. Includes overhunting (mammals) and the burgeoning pet trade.

• Exotic and Invasive Species:

  • Exotic: A non-native species introduced to a new area (not always harmful).

  • Invasive: An exotic species that grows to a large population size and disrupts native biological communities through competition, predation, or disease.

• Pollution: The release of persistent chemicals into ecosystems.

  • Biomagnification: The process where pesticides and herbicides become more concentrated as they move up the food chain.

  • Eutrophication: Caused by nitrogen ($N$) and phosphorus ($P$) runoff from farms into water bodies, leading to excessive algal growth.

Climate Change Impacts

• Habitat Disappearance: Polar and alpine habitats are physically vanishing.

• Sea Level Rise: Coastal habitats are threatened by the melting of glaciers and polar caps.

• Ocean Impacts:

  • Coral Bleaching: High temperatures cause corals to expel symbiotic algae, leading to widespread trophic cascades.

  • Ocean Acidification: Caused by rising atmospheric $CO_2$ reacting with seawater to form carbonic acid.

• Species-Area Relationship: Quantifies the link between species richness ($S$) and habitat area ($A$) using the formula:     $S = cA^z$

  • Where $S$ is the number of species, $A$ is the area, $c$ is a scaling constant, and $z$ is the slope of the line. Projections of habitat loss use this formula to estimate extinction rates, though it may sometimes overestimate them.

Conservation and Preservation Strategies

• Sustainability: Using resources at a rate at which they can be naturally replaced.

• Preservation Requirements: Impossible to maintain diversity if human population reaches $10 \text{ billion}$ or if fossil fuel/resource consumption in industrialized nations does not decline.

• Genetic Restoration: Use of artificial gene flow to assist small, isolated populations.

  • Example: Texas panthers were introduced to the Florida panther population; the resulting hybrids had fewer defects.

• Other Strategies:

  • Seed Banks: Long-term storage of seeds to preserve genetic diversity.

  • Ex Situ Conservation: Preserving species in artificial settings like zoos.

  • Economic Valuation: The cost of replacing lost ecosystem services is estimated to be $10 \times$ to $100 \times$ higher than the cost of maintaining them.

Class Notes: Parasitism and Behavioral Manipulation

• Malaria Model: Caused by 5 species of Plasmodium.

  • Sickens $249 \text{ million}$ people per year; the deadliest species kills approximately $600,000$ people annually.

  • Arms Race 1: Public health versus Plasmodium/Mosquitoes.

    • Mosquitoes developed resistance to DDT and insecticides.

    • Plasmodium developed resistance to Chloroquine, Mefloquine, and Quinine-derived drugs.

  • Current Strategy: Insecticide-impregnated bed nets. Because mosquitoes bite at night, the physical barrier prevents interaction without creating the same selective pressure for resistance as chemical sprays.

  • Behavioral Data: Research shows Plasmodium influences mosquito behavior to maximize transmission:

• Toxoplasma: Manipulates rats so they approach cats (their predator) to ensure the parasite can transition to its feline host. Infected rats show a preference for cat urine over rabbit or rat urine.

The Evolution of Virulence

• Virulence: The tendency of a parasite to cause death to its host.

• Key Observations:

  1. Virulence is a function of the parasite's growth rate (how many host cells are killed).

  2. Transmission probability is a function of the number of parasites present.

  3. There is heritable variation in host virulence.

• Trade-off: High virulence (killing hosts quickly) requires high transmission rates because the parasite cannot survive without a host. If transmission rates are low, parasites evolve to be more benign (less virulent) to keep the host alive long enough to find a new one.

Resilience and Solutions to Environmental Change

• Species Responses: Move to a new area, Acclimate/Adapt, or Die.

• Survival Factors:

  • Niche Size: Organisms with larger fundamental niches (broad tolerance) are more likely to survive.

  • Reproductive Characteristics: Organisms with high reproductive rates, short generation times, and large population sizes have more mutations and opportunities to adapt.

  • Vulnerability: Species with low reproductive rates and slow maturation are unlikely to survive rapid changes.

• Proposed Solutions:

  • Carbon Mitigation: Green/sustainable cities (green roofs, public transport, solar power), new fuels (Hydrogen, Fusion), and Carbon Capture (Kelp farming, reforestation, direct air absorption).

  • Management: Protecting biodiversity hotspots, artificial gene flow, and global population recovery programs.

  • Collaboration: Community science for data collection and informed collective action.