University Bio 180 Week 8: Biodiversity and Species Interactions Definitive Guide to Species Interactions

Biodiversity and Ecosystem Metrics

• Genetic Diversity: This refers to the total genetic information contained within all individuals of a group.

  • Increasing Diversity: Mutations that create new alleles increase genetic diversity.

  • Decreasing Diversity: Natural selection, genetic drift, and gene flow serve to decrease genetic diversity.

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

  • Geographical Trends: Species richness is often highest in the tropics and declines as one moves towards the poles.

• Species Diversity: A metric that considers both species richness and evenness (the relative abundance of each species present).

  • High Species Diversity: Indicates high evenness across species.

  • Low Species Diversity: Indicates low evenness, often meaning one species is dominating the environment.

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

• Phylogenetic Diversity: Specific species provide a community with evolutionary distinctiveness because they are phylogenetically distant from other species.

• Functional Diversity: Species possess functional traits that play specific roles in the function of an ecosystem.

  • Groups: Includes keystone species and nitrogen fixers.

• Ecosystem Diversity: A measure of the combination of horizontal and vertical diversity within an ecosystem.

• Ecosystem Function: The sum of biological and chemical processes characteristic of an ecosystem.

  • Processes: Includes primary production, nitrogen cycling, decomposition, and carbon storage.

  • Factors: Changes in climate or other physical conditions result in the formation of new ecosystems or ecosystem functions.

• Distribution Patterns: Biodiversity is generally higher on land than in the sea. This is attributed to the fact that areas with greater geographical variation tend to have higher biodiversity.

• Endemic Species: These are species found in a particular area and nowhere else on Earth.

• Biodiversity Hotspot: Regions in urgent need of conservation due to their high levels of biodiversity and threat levels.

Ecosystem Productivity and Stability

• Net Primary Productivity (NPP): This is crucial as it serves as the source of chemical energy used by species throughout a food web.

  • Relationship with Diversity: To a certain extent, increasing species richness and functional diversity increases NPP.

• Three Hypotheses for Increased NPP through Species Richness:

  1. Resource Use Efficiency: Diverse ranges of species use resources more efficiently because they possess non-overlapping niches.

  2. Facilitation: Certain species provide specific benefits that make the environment more favorable for other species (e.g., providing nutrients or partial shade).

  3. Sampling Effect: This occurs when one or two high-productivity species make high-species-richness plots outproduce low-species plots simply by random chance.

• Stability Metrics:

  • Resistance: The extent to which a community remains unchanged following a disturbance. This involves maintaining productivity and other ecosystem functions as conditions change.

  • Resilience: How quickly a community recovers its former levels of productivity or species richness following a disturbance.

• Natural Experiment: Comparison groups created by an unplanned and unmanipulated change in conditions.

• Stressors: Biodiversity provides resistance and resilience against climate extremes and other stressors like invasive species.

Ecosystem Services and Human Ethics

• Ecosystem Services: Direct and indirect benefits humans derive from organisms and the ecosystems they compose.

  • Provisioning Services: Raw materials such as food, fuel, fiber, medicine, and water.

    • Bioprospecting: The exploration of organisms as sources of drugs or ingredients in products, particularly medicine.

  • Regulating Services: Parts of Earth’s life support system, including climate moderation, soil formation, $O_2/CO_2$ regulation, water purification, air cleaning, and waste decomposition.

  • Supporting Services: Services that enable other ecosystem services, such as primary productivity, nutrient cycling, pollination, and pest control. These are noted as extremely difficult for humans to replicate on their own if they disappeared.

  • Cultural Services: Services that enrich the quality of life, including aesthetics, recreation, education, and spiritual value.

• Ethical Obligations to Preserve Biodiversity:

  1. Organisms possess intrinsic worth.

  2. Industrialized nations are responsible for the majority of environmental harm, yet poor countries are often the most affected.

  3. Future generations will be deprived of essential ecosystem services.

Fundamentals of Species Interactions

• Interaction Types:

  1. Commensalism ($+ / 0$): One species benefits while the other is unaffected.

  2. Competition ($- / -$): Individuals use the same resources, resulting in lower fitness for both parties.

  3. Consumption ($+ / -$): One organism eats or absorbs nutrients from another; fitness increases for the consumer and decreases for the victim. Includes predation.

  4. Mutualism ($+ / +$): Two species help each other, increasing fitness for both.

• Key Themes:

  • Interactions affect species distribution and abundance.

  • Species act as agents of natural selection during interaction, leading to Coevolution (reciprocal influence on adaptations over time).

  • Outcomes of interactions are dynamic and conditional.

Commensalism and Competition Details

• Commensalism Characteristics:

  • Challenging to demonstrate because the absence of fitness benefit or cost is difficult to quantify.

  • Very conditional in nature.

  • Example: Epiphytic orchids attach to trees to benefit from sunlight and better access to water/nutrients while the tree is unaffected.

• Competition Dynamics:

  • Cost: Competing is energetically costly. Any energy spent in competition reduces the amount available for foraging, mating, and reproduction. It is theoretically better for a species to avoid competition entirely.

  • Intraspecific Competition: Occurs between members of the same species, often seen during density-dependent growth.

  • Interspecific Competition: Occurs between different species and can be direct or indirect.

• The Niche Concept:

  • Definition: The range of resources a species can use or the conditions it can tolerate.

  • Niche Overlap: When niches overlap, interspecific competition develops. The extent of competition depends on the extent of the overlap.

  • Competitive Exclusion Principle: Two species cannot occupy the exact same niche. The outcompeted species must either change its niche or face extinction.

  • Fundamental Niche: The theoretical range of environmental/abiotic conditions a species can tolerate. Extreme abiotic factors lead to more specific fundamental niches, often making species more likely to be closely related.

  • Realized Niche: The portion of the fundamental niche a species actually occupies when biotic limiting factors (like competition) are present.

• Fitness Trade-offs: Inevitable compromises in adaptation. Investing in the ability to compete for one resource requires time/energy that cannot be invested in other fitness-contributing traits.

  • Barnacle Example: Chthamalus lives in the upper intertidal zone, and Semibalanus lives in the lower intertidal zone. Semibalanus outcompetes Chthamalus overall but cannot endure the abiotic conditions of the upper intertidal. Thus, Chthamalus occupies a small realized niche where Semibalanus cannot survive.

• Environmental Dependence: Competitive ability is not an inherent quality; it depends on environmental conditions. A species highly competitive in one environment may be neutral or inferior in another.

• Niche Differentiation/Resource Partitioning: An evolutionary change in resource use caused by competition over generations. Natural selection favors traits that avoid the fitness cost of competition.

• Character Displacement: Evolutionary change in species traits that enables species to exploit different resources.

Consumption Interactions

• Classification of Consumption:

  1. Predation: A predator kills and consumes all of the prey's body (typically carnivores).

  2. Herbivory: An herbivore consumes plant or algal tissues. It may not consume the entire organism, though it can be fatal depending on damage.

  3. Parasitism: A parasite takes resources from a host.

     • Endoparasite: Consumes small amounts of tissue/nutrients from inside the host; usually small relative to host and not immediately fatal (e.g., tapeworms).

     • Ectoparasite: Consumes fluids/tissue from the outside of the host (e.g., ticks).

     • Parasitoid: Free-living as an adult but parasitic as a larva. Larvae hatch from eggs laid on/in a host and consume it entirely, which is fatal (e.g., parasitoid wasps).

• Measuring Consumption Consequences:

  • Excluding predators from an area and observing prey abundance changes.

  • Looking at correlations in natural environments.

• Integrated Pest Management (IPM): Strategies to maximize productivity while minimizing insecticides, such as introducing natural predators of a pest.

• Coevolutionary Arms Race: A repeating cycle of reciprocal adaptation where species constantly adapt to each other's survival strategies.

• Defensive Strategies:

  • Constitutive (Standing) Defenses: Present even in the absence of consumers. Includes cryptic coloration/object resemblance, escape behavior, toxins, defense armor (shells/thorns), and schooling/flocking. These are effective but energy-costly.

  • Inducible Defenses: Defensive traits induced only in response to a consumer. They decline in the absence of the consumer. These are energetically efficient but slow to produce.

• Mimicry Types:

  • Batesian Mimicry: Natural selection favors a mimic species that resembles an unpalatable species despite being nontoxic/palatable itself.

  • Müllerian Mimicry: Natural selection favors mimic species that are both unpalatable. This increases the likelihood predators avoid them and boosts fitness for both species.

• Host-Parasite Coevolution Example: Roundworms lay eggs in the abdomen of an ant, causing it to swell and look like a red berry. Birds eat the ant, the roundworms grow inside the bird, and they are dispersed through feces to be consumed by ants again.

Mutualism and Symbiosis

• Definitions:

  • Symbiosis: Any physically close association between two species (can be $/+$, $/-$ or $/0$). Parasitism is a form of symbiosis.

  • Mutualism: A byproduct of two individuals pursuing self-interest to maximize their own fitness. It is not altruism and can be thought of as "mutual parasitism."

• Examples:

  • Orange nectar bats carrying pollen between plants while drinking nectar.

  • Mycorrhizal fungi receiving sugars/carbon in exchange for providing nitrogen and phosphorus to plants.

• Cheating in Mutualism: Some species "cheat" the system (e.g., deceit pollination where a plant has no nectar, or nectar robbers who pierce the flower side to bypass pollination), turning the interaction into $+ / -$.

• Context Dependence: In low-nitrogen soil, plant investment in root nodules for bacteria is a $+ / +$ interaction. In high-nitrogen soil, the energetic cost to the plant may outweigh the benefit, making it $+ / -$.

• Pollinator Strategy:

  • Specialists: High fitness from adapting to one flower, but high extinction risk if that flower disappears.

  • Generalists: Less efficient feeders but more likely to persist in variable conditions.

Class Notes and Summary Comparisons

• Primary Productivity Math:

  • Gross Primary Productivity (GPP): Total sunlight energy captured.

  • Net Primary Productivity (NPP): Sunlight energy used for growth.

  • Formulaic Relationship: NPP < GPP because energy is lost to respiration, repair, and anti-herbivory.

  • Measurement: NPP is measured by biomass (weight).

• Productivity Distribution: Tropical rainforests and open oceans contribute the most to global NPP.

• Diversity and Biomass: Both richness and the number of functional groups increase biomass, but only to a saturation point before plateauing due to finite resources.

• Competition and Population: Even when one species outcompetes another, both populations are lower than they would be in the absence of competition because of resource consumption and energy costs of competing.

• Mycorrhizal Case Study:

  • Plants provide carbon (sugars) and fungi provide nutrients ($N$ and $P$).

  • Experiment: Radioactive carbon measurement showed plants transferred equal amounts of carbon regardless of exposure levels. This suggests an asymmetrical exchange where fungi may be more "stingy" with phosphorus than plants are with carbon.

  • Pinedrop Plant: An example of parasitism in angiosperms; it stops contributing to the fungal network but continues to take from it.

• Phylogenetic Review:

  • Parsimony: Choosing the simplest explanation with the fewest evolutionary changes.

  • Homology: Traits inherited from a common ancestor (e.g., backbones in vertebrates).

  • Homoplasy: Traits that evolve independently in separate lineages (convergent evolution).

  • Synapomorphy: A derived homology unique to a particular clade used to identify it (e.g., hair for mammals). Note: All synapomorphies are homology, but not all homologies are synapomorphies (e.g., a backbone is homology but not a synapomorphy for mammals because other groups have them).

• Plant Innovations:

  1. Vascular Tissue: Allows transport against gravity (plants grow taller).

  2. Cuticle: Waxy layer preventing water loss.

  3. Pores and Stomata: Openings for gas exchange.

  4. Seeds and Pollen: Protection and prevention of desiccation.

  5. Flowers: Reproductive innovation.

• Speciation Factors: Genetic isolation (gene flow stops) and genetic divergence (mutation, selection, and drift).

• Niche Differentiation vs. Character Displacement:

  • Niche Differentiation: Changing the realized niche to reduce competition (behavioral/usage change).

  • Character Displacement: Changing physical traits to adapt to those niches (evolutionary change in traits).