🐼Conservation Biology Unit 5 – Species Interactions in Community Ecology

Key Concepts and Definitions

• Species interactions involve the relationships and effects that species have on one another within a community
• Community ecology studies the interactions and dynamics among species within a shared environment or habitat
• Interspecific interactions occur between individuals of different species (competition, predation, mutualism)
• Intraspecific interactions occur between individuals of the same species (competition for resources, cooperation)
• Ecological niche refers to the role and position a species occupies within its environment, including its resource use and interactions
• Fundamental niche represents the full range of conditions and resources a species could potentially utilize in the absence of competition or other constraints
• Realized niche is the actual niche a species occupies in the presence of interactions and constraints from other species and environmental factors

Types of Species Interactions

• Competition involves species vying for limited resources, leading to negative effects on one or both species (lions and hyenas competing for prey)
• Predation occurs when one species (predator) hunts, kills, and consumes another species (prey) for sustenance (wolves preying on elk)
• Herbivory is a form of predation where animals feed on plants (rabbits grazing on grass)
• Mutualism is an interaction where both species benefit from the relationship (bees pollinating flowers while gathering nectar)
• Commensalism involves one species benefiting while the other is unaffected (barnacles attaching to whales for transportation)
• Parasitism occurs when one species (parasite) lives on or within another species (host), causing harm to the host (ticks feeding on the blood of mammals)
• Amensalism is an interaction where one species is harmed while the other is unaffected (allelopathic plants releasing chemicals that inhibit the growth of nearby plants)

Ecological Niches and Resource Partitioning

• Ecological niche includes the resources a species uses, its role in the ecosystem, and how it interacts with other species
• Resource partitioning is the division of resources among species to minimize competition and allow coexistence
  • Occurs when species specialize in using different parts of a shared resource (different bird species feeding on different parts of the same tree)
• Niche differentiation allows species to occupy distinct niches and reduce direct competition
• Niche overlap occurs when species have similar resource requirements and can lead to increased competition
• Competitive exclusion principle states that two species with identical niches cannot coexist indefinitely, as one will eventually outcompete the other
• Character displacement is the process by which species evolve different traits or resource use to minimize competition and allow coexistence (Darwin's finches developing different beak shapes to feed on different seeds)

Competition and Coexistence

• Interspecific competition occurs when different species compete for the same limited resources
  • Exploitation competition involves species indirectly competing by consuming the same resources (two herbivore species grazing on the same plants)
  • Interference competition occurs when species directly prevent others from accessing resources through aggressive behavior or territoriality (one ant species defending its nest against another)
• Competitive exclusion can lead to the local extinction of the less competitive species
• Coexistence mechanisms allow species to persist together despite competition
  • Resource partitioning and niche differentiation reduce direct competition
  • Spatial partitioning involves species using different microhabitats or areas within the same larger habitat (different bird species nesting at different heights in the same forest)
  • Temporal partitioning occurs when species use resources at different times (diurnal and nocturnal predators hunting at different times of day)
• Keystone species have disproportionately large effects on the community relative to their abundance and can promote coexistence by regulating dominant species (sea otters controlling sea urchin populations, allowing kelp forests to thrive)

Predator-Prey Dynamics

• Predator-prey interactions involve predators consuming prey species, affecting the populations of both
• Predators can regulate prey populations and prevent overexploitation of resources
• Prey species evolve defenses against predation, such as camouflage, warning coloration, or chemical defenses
• Predator-prey cycles involve the oscillation of predator and prey populations over time (lynx and hare populations in the boreal forest)
  • As prey populations increase, predator populations also grow due to increased food availability
  • High predator populations then reduce prey numbers, leading to a subsequent decline in predator populations
• Trophic cascades occur when changes in predator populations indirectly affect multiple levels of the food web (reintroduction of wolves in Yellowstone affecting elk, vegetation, and other species)
• Mesopredator release happens when the removal of top predators leads to an increase in medium-sized predators, which can then impact lower trophic levels (coyote populations increasing in the absence of wolves)

Mutualism and Symbiosis

• Mutualism is an interaction where both species benefit from the relationship
  • Obligate mutualism is when species are entirely dependent on each other for survival (fig wasps and fig trees)
  • Facultative mutualism occurs when species benefit from the interaction but can survive independently (ants protecting aphids from predators in exchange for honeydew)
• Symbiosis is a close and long-term interaction between two species, which can be mutualistic, commensalistic, or parasitic
• Endosymbiosis involves one species living within the cells or tissues of another (nitrogen-fixing bacteria in the roots of legumes)
• Ectosymbiosis occurs when one species lives on the surface of another (cleaner fish removing parasites from larger fish)
• Coevolution is the process by which species evolve in response to each other, leading to specialized adaptations (long nectar tubes in flowers and elongated beaks in hummingbirds)

Community Structure and Biodiversity

• Community structure refers to the composition, diversity, and interactions of species within a community
• Species richness is the number of different species present in a community
• Species evenness describes the relative abundance of each species within the community
• Biodiversity encompasses the variety of life at all levels, including genetic, species, and ecosystem diversity
• Trophic levels organize species based on their position in the food chain (producers, primary consumers, secondary consumers, etc.)
• Food webs depict the complex feeding relationships among species in a community
• Ecological succession is the process by which communities change over time, with species composition shifting as the environment changes (primary succession on a newly formed volcanic island)
  • Pioneer species are the first to colonize a new or disturbed area, often with adaptations for dispersal and rapid growth
  • Climax communities represent the stable, mature stage of succession, with long-lived and competitively dominant species

Conservation Implications

• Species interactions play a crucial role in maintaining ecosystem function and biodiversity
• Habitat loss and fragmentation can disrupt species interactions and lead to cascading effects on the community (deforestation affecting plant-pollinator relationships)
• Invasive species can outcompete native species and alter community dynamics (kudzu vine smothering native vegetation in the southeastern United States)
• Overexploitation of keystone species can have far-reaching impacts on the ecosystem (overfishing of sharks affecting coral reef communities)
• Climate change can shift species ranges, phenology, and interactions, leading to community reorganization (earlier spring arrival affecting plant-pollinator synchrony)
• Ecological restoration aims to restore degraded ecosystems and re-establish species interactions (reintroducing native plant species to restore pollinator communities)
• Ecosystem-based management considers the complex interactions among species and their environment when developing conservation strategies
• Maintaining and promoting biodiversity is essential for preserving the resilience and functioning of ecosystems in the face of environmental change