🦉Intro to Ecology Unit 7 – Species Interactions and Coexistence

Key Concepts

• Species interactions play a crucial role in shaping ecological communities and ecosystems
• Interactions can be classified as positive, negative, or neutral based on their effects on the involved species
• Competition occurs when two or more species vie for the same limited resources (food, habitat, mates)
• Predation involves one species (predator) consuming another species (prey) as a source of energy and nutrients
• Symbiosis refers to close and long-term interactions between two or more species, which can be mutualistic, commensalistic, or parasitic
• Coexistence is the ability of multiple species to persist together in the same habitat over time
• Niche partitioning allows species to coexist by reducing competition through the utilization of different resources or habitats
• Community structure and diversity are influenced by the complex network of species interactions within an ecosystem

Types of Species Interactions

• Competition is a negative interaction where species compete for limited resources, leading to reduced fitness or population sizes
• Predation is a negative interaction where one species (predator) benefits by consuming another species (prey)
• Herbivory is a type of predation where animals (herbivores) feed on plants or algae
• Mutualism is a positive interaction where both species benefit from the relationship (pollination, seed dispersal)
• Commensalism is a positive interaction where one species benefits while the other is unaffected (barnacles on whales)
• Parasitism is a negative interaction where one species (parasite) benefits at the expense of another (host)
• Amensalism is a negative interaction where one species is harmed while the other is unaffected (allelopathy in plants)
• Neutralism occurs when two species interact but have no significant effect on each other

Competition and Coexistence

• Interspecific competition occurs between individuals of different species, while intraspecific competition occurs within the same species
• The competitive exclusion principle states that two species competing for the same resources cannot coexist indefinitely
• Resource partitioning allows species to coexist by utilizing different resources or habitats, reducing competition
  • Spatial partitioning involves using different microhabitats or foraging areas
  • Temporal partitioning involves using resources at different times (diurnal vs. nocturnal activity)
• Character displacement is the divergence of traits (morphological, ecological, or behavioral) in sympatric species to minimize competition
• Coexistence can be facilitated by trade-offs between competitive ability and other traits (colonization, stress tolerance)
• Niche differentiation promotes coexistence by reducing niche overlap and competition between species

Predator-Prey Dynamics

• Predator-prey interactions can lead to population oscillations, with predator populations tracking prey populations
• The Lotka-Volterra model describes the dynamics of predator-prey interactions using differential equations
• Predators can exert top-down control on prey populations, regulating their numbers and indirectly affecting lower trophic levels
• Prey species have evolved various defenses against predation, such as camouflage, mimicry, chemical defenses, and group behavior
• Predators have evolved adaptations to locate, capture, and consume prey efficiently (keen senses, speed, venom)
• Trophic cascades occur when changes in predator populations indirectly affect multiple trophic levels in an ecosystem
• Keystone predators have disproportionately large effects on community structure and diversity relative to their abundance

Symbiotic Relationships

• Mutualism involves both species benefiting from the interaction, such as pollination and nitrogen fixation in legume-rhizobia symbiosis
• Commensalism occurs when one species benefits while the other is unaffected (epiphytes on trees, remora fish on sharks)
• Parasitism involves one species (parasite) benefiting at the expense of another (host), such as tapeworms in mammals or mistletoes on trees
  • Parasites can reduce host fitness, alter behavior, and regulate host populations
  • Parasitoids are insects that lay eggs in or on a host, ultimately killing it (wasps and caterpillars)
• Symbiotic relationships can evolve over time, with partners becoming increasingly dependent on each other
• Coevolution occurs when two or more species reciprocally affect each other's evolution (flowers and pollinators)

Community Structure and Diversity

• Communities are assemblages of interacting populations of different species in a particular area
• Species richness refers to the number of different species present in a community
• Species evenness describes the relative abundances of different species within a community
• Alpha diversity is the diversity within a single community or habitat, while beta diversity is the change in species composition between communities
• Interactions among species (competition, predation, mutualism) shape community structure and composition
• Disturbances (fires, storms, human activities) can alter community structure and diversity by creating opportunities for colonization and succession
• Biodiversity is important for ecosystem functioning, stability, and resilience to environmental changes

Ecological Niches

• An ecological niche is the role and position a species occupies within an ecosystem, including its resource use, interactions, and environmental tolerances
• The fundamental niche is the full range of conditions and resources a species could potentially use in the absence of competition and other biotic interactions
• The realized niche is the actual range of conditions and resources a species uses in the presence of biotic interactions and constraints
• Niche breadth refers to the range of resources a species can use or the variety of conditions it can tolerate
• Niche overlap occurs when two or more species use similar resources or occupy similar ecological roles
• Niche partitioning reduces competition and allows for coexistence by dividing resources among species
• Specialist species have narrow niches and are adapted to specific resources or conditions, while generalist species have broad niches and can use a wide range of resources

Real-World Applications and Case Studies

• Understanding species interactions is crucial for conservation efforts, as the loss of one species can have cascading effects on others
• Invasive species can disrupt native communities through competition, predation, or habitat modification (kudzu in the southeastern United States, Burmese pythons in the Everglades)
• Biological control involves using natural predators, parasites, or pathogens to manage pest populations (ladybugs to control aphids)
• Restoration ecology aims to restore degraded ecosystems by reintroducing key species and managing interactions (reintroduction of wolves in Yellowstone)
• Climate change can alter species interactions and community structure by shifting ranges, phenology, and resource availability (earlier spring arrival affecting plant-pollinator interactions)
• Agroecology applies ecological principles to design sustainable agricultural systems that leverage beneficial species interactions (intercropping, cover crops)
• Urbanization can create novel ecosystems with altered species interactions and community structure (urban bird communities, green roofs)