🪺Environmental Biology Unit 4 – Community Ecology & Species Interactions

Key Concepts in Community Ecology

• Community ecology focuses on the interactions between species and how they shape the structure and function of ecological communities
• Includes the study of species diversity, abundance, and distribution within a given area or habitat
• Examines the roles of biotic factors (living organisms) and abiotic factors (non-living components) in shaping community dynamics
• Explores the concept of ecological niches, which refers to the specific role and resource requirements of a species within its community
  • Includes the species' habitat preferences, food sources, and interactions with other organisms
• Investigates the mechanisms of species coexistence, such as resource partitioning and niche differentiation
• Analyzes the effects of interspecific competition, predation, and mutualism on community structure and stability
• Studies the concept of keystone species, which have a disproportionately large influence on the community relative to their abundance (sea otters in kelp forests)
• Examines the role of disturbances, such as fires and storms, in shaping community composition and dynamics

Types of Species Interactions

• Competition occurs when two or more species vie for the same limited resources, such as food, water, or space
  • Interspecific competition happens between different species (lions and hyenas competing for prey)
  • Intraspecific competition occurs within the same species (two male birds competing for a mate)
• Predation is an interaction where one species (the predator) hunts, kills, and consumes another species (the prey)
  • Predators can influence prey populations and shape community structure (wolves regulating elk populations)
• Herbivory is a type of predation where animals feed on plants, affecting plant growth and reproduction
• Parasitism is a relationship in which one species (the parasite) lives on or within another species (the host), causing harm to the host (tapeworms in the human digestive system)
• Mutualism is a symbiotic relationship where both species benefit from the interaction (bees pollinating flowers while collecting nectar)
• Commensalism is an interaction where one species benefits while the other is unaffected (barnacles attaching to whales for transportation)
• Amensalism occurs when one species is harmed while the other is unaffected (allelopathy, where plants release chemicals that inhibit the growth of other plants)

Community Structure and Composition

• Community structure refers to the physical organization and arrangement of species within a community
  • Includes the vertical stratification of species (canopy, understory, and forest floor in a rainforest)
  • Also considers the horizontal distribution of species across a landscape (patches of different habitats)
• Community composition describes the variety and abundance of species present in a community
• Species richness is the number of different species found within a community
• Species evenness refers to how evenly individuals are distributed among the different species in a community
• Dominant species are those that have the greatest influence on community structure and function due to their abundance or biomass (kelp in a kelp forest)
• Foundation species play a critical role in creating and maintaining habitats that support other species (coral in a coral reef)
• Indicator species are sensitive to environmental changes and can be used to assess the health of a community (lichens as indicators of air quality)

Ecological Succession

• Ecological succession is the gradual process by which species composition and community structure change over time
• Primary succession occurs in newly formed or bare habitats, such as volcanic islands or glacial moraines
  • Pioneer species are the first to colonize these areas, often hardy plants that can tolerate harsh conditions
• Secondary succession happens in previously occupied habitats that have been disturbed, such as abandoned agricultural fields or areas affected by wildfires
  • Begins with the establishment of fast-growing, opportunistic species that quickly colonize the disturbed area
• Succession progresses through several stages, from early pioneer communities to more complex, mature communities
• Climax communities are relatively stable and self-sustaining, representing the final stage of succession in a given environment (old-growth forests)
• Disturbances, such as fires, storms, or human activities, can reset or alter the successional process
• Understanding succession is crucial for ecosystem management, restoration, and predicting community responses to environmental changes

Biodiversity and Its Importance

• Biodiversity refers to the variety of life at all levels, from genes to ecosystems
  • Genetic diversity is the variation in genes within a species or population
  • Species diversity is the number and abundance of different species in a community or ecosystem
  • Ecosystem diversity encompasses the variety of habitats, communities, and ecological processes
• Biodiversity is essential for maintaining ecosystem functions and services, such as nutrient cycling, pollination, and climate regulation
• High biodiversity can increase ecosystem stability and resilience to disturbances and environmental changes
• Biodiversity provides numerous benefits to humans, including food, medicine, and raw materials for various industries
• Loss of biodiversity can have far-reaching consequences, such as reduced ecosystem functioning, decreased resilience, and potential cascading effects on other species
• Major threats to biodiversity include habitat loss and fragmentation, overexploitation, invasive species, pollution, and climate change
• Conservation efforts aim to protect and restore biodiversity through various strategies, such as habitat preservation, species management, and sustainable resource use

Trophic Levels and Food Webs

• Trophic levels represent the position of an organism in a food chain or food web based on its feeding relationships
  • Primary producers (autotrophs) form the base of the trophic structure, converting solar energy into organic compounds through photosynthesis (plants, algae)
  • Primary consumers (herbivores) feed on primary producers (rabbits, zooplankton)
  • Secondary consumers (carnivores) feed on primary consumers (foxes, small fish)
  • Tertiary consumers (top predators) feed on secondary consumers (eagles, sharks)
  • Decomposers break down dead organic matter and recycle nutrients back into the ecosystem (bacteria, fungi)
• Food chains are linear sequences of trophic levels, showing the flow of energy from producers to consumers
• Food webs are more complex, depicting the interconnected feeding relationships among species in an ecosystem
• Energy transfer between trophic levels is inefficient, with only about 10% of the energy being passed on to the next level
• Biomass and energy decrease at higher trophic levels, resulting in pyramid-shaped diagrams (ecological pyramids)
• Trophic cascades occur when changes in one trophic level affect multiple other levels, often due to predator-prey interactions (reintroduction of wolves in Yellowstone)

Ecosystem Stability and Resilience

• Ecosystem stability refers to the ability of an ecosystem to maintain its structure and function in the face of disturbances or environmental changes
• Resistance is the capacity of an ecosystem to withstand disturbances without undergoing significant changes in its composition or functioning
• Resilience is the ability of an ecosystem to recover and return to its original state after being disturbed
• Factors that contribute to ecosystem stability and resilience include biodiversity, functional redundancy, and the presence of keystone species
  • Functional redundancy occurs when multiple species perform similar roles within an ecosystem, providing a buffer against species loss
• Disturbances can be natural (fires, storms) or anthropogenic (pollution, land-use changes) and vary in intensity, frequency, and scale
• Ecosystem stability and resilience are important for maintaining ecosystem services and supporting human well-being
• Monitoring ecosystem responses to disturbances can provide insights into their stability and resilience and inform management strategies
• Enhancing ecosystem stability and resilience is a key goal of conservation and restoration efforts, particularly in the face of global environmental changes

Human Impacts on Ecological Communities

• Human activities have profound effects on ecological communities and biodiversity worldwide
• Habitat loss and fragmentation are major threats, resulting from land-use changes such as deforestation, urbanization, and agricultural expansion
  • Fragmentation can isolate populations, reduce gene flow, and increase the risk of local extinctions
• Overexploitation of species through hunting, fishing, and harvesting can lead to population declines and ecosystem imbalances (overfishing of cod in the Atlantic)
• Introduction of invasive species, either intentionally or accidentally, can disrupt native communities and cause biodiversity loss (kudzu vine in the southeastern United States)
• Pollution, including air, water, and soil contamination, can have detrimental effects on species and ecosystem functioning (DDT affecting bird populations)
• Climate change, largely driven by human activities, is altering environmental conditions and shifting species distributions, leading to community reorganization and potential extinctions
• Urbanization can create novel ecosystems with altered species composition and interactions, such as urban heat islands and modified hydrological cycles
• Human-induced disturbances can interact and amplify their effects on ecological communities, requiring a holistic approach to conservation and management
• Mitigating human impacts involves sustainable resource management, habitat protection and restoration, pollution control, and climate change mitigation and adaptation strategies