45.6 Community Ecology
5 min read•june 14, 2024
and symbiotic interactions shape ecosystems. These dynamics influence population sizes, drive , and create complex . Understanding these relationships is crucial for grasping how communities function and evolve over time.
Community structure forms through succession, competition, and . From barren landscapes to mature forests, ecosystems develop in stages. This process highlights the interconnectedness of species and their environment, showcasing nature's resilience and adaptability.
Community Interactions and Dynamics
Dynamics of predator-prey relationships
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- Predators hunt and consume prey species regulating prey populations through direct mortality
- Prey availability influences predator population sizes as predators depend on sufficient prey for survival and reproduction
- mathematically describes cyclic fluctuations in predator and prey populations over time
- Prey populations increase when predators are scarce due to reduced predation pressure leading to a subsequent increase in predator populations as more food becomes available
- As predator populations rise they reduce prey populations through increased consumption eventually causing a decline in predator numbers due to food scarcity
- occur when changes in predator populations indirectly affect multiple trophic levels in the ecosystem (plants, herbivores)
- Removal of top predators (wolves) may lead to overgrazing by herbivores (elk) and alter plant community structure and diversity
- are predators that have a disproportionately large impact on community structure and function relative to their abundance
- Their removal can lead to significant changes in the ecosystem such as increased herbivory and reduced plant diversity (sea otters in kelp forests)
- Food webs illustrate the complex feeding relationships and energy flow within a community, including predator-prey interactions
Adaptations against predation and herbivory
- Physical defenses deter predators and herbivores
- Spines (cacti), thorns (roses), and tough exoskeletons (beetles) make organisms difficult to consume
- (leaf insects) and (king snakes) help organisms blend in with their environment or resemble unpalatable species to avoid detection
- Chemical defenses discourage consumption by predators and herbivores
- Toxic or distasteful compounds (monarch butterfly) make organisms unpalatable or poisonous
- Some plants produce secondary metabolites such as tannins (oak trees) or alkaloids (coffee) to reduce herbivory by making tissues difficult to digest or toxic
- Behavioral defenses help organisms avoid or escape predation
- Fleeing or hiding from predators (rabbits, mice)
- Forming groups or herds (wildebeest) to reduce individual risk of predation through dilution effect and increased vigilance
- (poison dart frogs) warns predators of an organism's unpalatability or toxicity to avoid costly encounters
Competitive exclusion principle in communities
- states that two species with identical ecological niches cannot coexist indefinitely in the same habitat
- Competition for limited resources (food, space) leads to the exclusion of the less competitive species over time
- allows species to evolve and specialize in different resources or microhabitats to avoid competition
- allows similar species to coexist in the same community by occupying different ecological roles (Darwin's finches)
- is the divergence of morphological, ecological, or behavioral traits in sympatric species to minimize competition
- Occurs when closely related species occupy the same geographic area and compete for resources leading to evolutionary changes that reduce niche overlap (Galapagos finches)
- can lead to the exclusion of less competitive species, influencing community composition and structure
Types of symbiotic relationships
- is a symbiotic relationship where both species benefit from the interaction
- Pollination: plants provide nectar and pollen to attract pollinators (bees) which in turn fertilize the plants allowing for reproduction
- Nitrogen fixation: legumes (soybeans) nitrogen-fixing bacteria in root nodules providing nutrients for the plant in exchange for carbohydrates
- is a symbiotic relationship where one species benefits while the other is unaffected
- Epiphytes (orchids) grow on trees benefiting from increased access to sunlight without harming the host tree
- Remora fish attach to larger fish (sharks) to gain transportation and protection without impacting the host
- is a symbiotic relationship where one species (the ) benefits at the expense of the other (the host)
- Parasites may reduce host fitness, growth, or survival by extracting resources
- Tapeworms live in the digestive tract of animals absorbing nutrients from the host leading to malnutrition and weight loss
- Mistletoes are parasitic plants that grow on trees extracting water and nutrients from the host potentially reducing growth and survival
Formation of community structure
- is the colonization and development of communities in previously uninhabited areas such as newly formed volcanic islands or glacial moraines
- such as lichens and mosses establish first and modify the environment for later successional stages by breaking down rocks and forming soil
- Grasses and herbaceous plants colonize the area as soil develops increasing organic matter and nutrient availability
- Shrubs and small trees begin to dominate the community as soil fertility improves shading out earlier successional species
- Mature forests develop as larger trees establish and create a complex canopy structure supporting diverse understory vegetation
- is the recovery of a community after a disturbance such as fire, logging, or abandonment of agricultural land
- Starts with existing soil and remnant organisms leading to faster community development compared to primary succession
- Grasses, forbs, and other herbaceous plants quickly colonize the disturbed area and begin to rebuild soil organic matter
- Shrubs and fast-growing trees (aspen) establish as soil fertility improves and outcompete earlier successional species
- Slower-growing, shade-tolerant trees (maple) gradually replace earlier successional species and develop a mature forest canopy
- Successional stages are characterized by changes in species composition and community structure over time
- Early successional species are typically fast-growing, opportunistic, and tolerant of harsh conditions (dandelions, fireweed)
- Late successional species are slower-growing, more competitive, and often more specialized in their resource requirements (oak, hickory)
- is the final, relatively stable stage of
- Composition is determined by regional climate and soil conditions and may persist for long periods until a major disturbance resets the successional process
- Examples include mature forests (temperate deciduous), grasslands (prairie), and wetlands (marsh) that have reached a dynamic equilibrium with the environment
- Ecological succession plays a crucial role in shaping community structure and over time
Community Resilience and Conservation
- Biodiversity contributes to community stability and resilience by providing functional redundancy and response diversity
- can disrupt community interactions and reduce biodiversity by isolating populations and limiting species movement
Key Terms to Review (43)
Adaptations: Adaptations are traits or characteristics that enhance the survival and reproductive success of organisms in their specific environments. These changes can be structural, behavioral, or physiological, allowing organisms to better cope with challenges in their surroundings, such as climate, food availability, and interactions with other species. Over time, adaptations arise through the process of natural selection, where favorable traits become more common within a population.
Aposematic coloration: Aposematic coloration refers to the bright and distinctive colors or patterns found in certain animals that serve as a warning to potential predators about their toxicity or unpalatability. This form of coloration plays a critical role in community interactions by helping to establish a relationship between prey and predator, reducing the likelihood of predation and influencing species diversity within an ecosystem.
Batesian mimicry: Batesian mimicry is a form of mimicry where a harmless species evolves to imitate the warning signals of a harmful species to deter predators. This evolutionary strategy increases the survival rate of the mimic by reducing its chances of being preyed upon.
Biodiversity: Biodiversity refers to the variety of life forms on Earth, encompassing the diversity of species, genetic variations, and ecosystems. This term is crucial as it helps us understand the intricate web of life, its functioning, and its significance in maintaining ecological balance and resilience.
Camouflage: Camouflage is a strategy used by organisms to blend in with their surroundings to avoid predation or to enhance predatory success. It involves coloration, patterns, and behaviors that help an organism become less visible to predators or prey.
Camouflage: Camouflage is a biological adaptation that allows an organism to blend into its environment, making it less visible to predators or prey. This adaptation is crucial for survival in various ecosystems, as it enhances an organism's ability to avoid detection and increases its chances of survival and reproduction. Camouflage can take many forms, including color patterns, textures, and shapes that mimic the surrounding habitat.
Character Displacement: Character displacement is a phenomenon where two species that share a habitat evolve different traits to minimize competition for resources. This process often occurs when species with similar needs coexist in the same area, leading them to adapt their characteristics over generations. The result is that these species become more distinct from each other in their physical traits or behaviors, which helps reduce overlap in resource use and promotes niche differentiation.
Climax community: A climax community is a stable and mature ecological community that has reached a stage of ecological succession where its structure and species composition remain relatively unchanged over time. This community is typically characterized by high biodiversity and complex interactions among organisms, and it reflects the regional climate and soil conditions. Climax communities are important because they represent the end point of ecological succession, demonstrating how ecosystems evolve and stabilize in response to environmental factors.
Commensal: Commensalism is a type of symbiotic relationship between two organisms where one benefits while the other is neither helped nor harmed. This relationship typically involves one organism gaining food, shelter, or transport from the other without negatively impacting it.
Commensalism: Commensalism is a type of symbiotic relationship where one organism benefits while the other is neither helped nor harmed. In fungal biology, this often involves fungi living on or within a host organism without causing it any harm.
Commensalism: Commensalism is a type of symbiotic relationship between two different organisms where one organism benefits while the other is neither helped nor harmed. This interaction can play a significant role in ecological communities, influencing species diversity and stability. Commensal relationships can be found in various ecosystems, where one species may find shelter or food from another without impacting its host negatively.
Community ecology: Community ecology is the study of how different species interact within a shared environment and how these interactions shape the structure and dynamics of the community. This field examines various relationships among species, such as competition, predation, and symbiosis, as well as how these relationships influence biodiversity and ecosystem functioning. Community ecology is essential for understanding ecological patterns and processes at local and global scales.
Competitive exclusion principle: The competitive exclusion principle states that two species competing for the same limiting resource cannot coexist at constant population values. This principle highlights the idea that if two species are competing for identical resources, one will eventually outcompete and eliminate the other. It underscores the importance of resource availability and niche differentiation in community ecology, influencing species distribution and abundance.
Ecological Succession: Ecological succession is the process by which ecosystems change and develop over time, leading to a series of progressive changes in the species composition and structure of a community. This process can occur in both terrestrial and aquatic environments and can be driven by various factors such as disturbances, climate changes, and species interactions. Understanding ecological succession helps illustrate how communities adapt to environmental changes and how biodiversity evolves over time.
Emsleyan/Mertensian mimicry: Emsleyan/Mertensian mimicry is a rare form of mimicry in which a deadly or highly toxic species mimics a less harmful one. This strategy confuses predators and can provide evolutionary advantages to the mimicking species.
Environmental disturbances: Environmental disturbances are events that disrupt the structure and function of an ecosystem, affecting population dynamics and community interactions. These can be natural or anthropogenic, such as fires, storms, or human activities like deforestation.
Food webs: Food webs are complex networks that illustrate how energy and nutrients flow through an ecosystem, connecting various organisms that interact as predators, prey, and decomposers. They highlight the relationships between different species, showing how they depend on one another for survival. This interconnectedness is crucial for understanding ecosystem dynamics, population control, and energy transfer.
Foundation species: Foundation species are organisms that play a crucial role in creating or maintaining the structure of an ecological community. Their presence and activities significantly influence the types and numbers of other species in a community.
Habitat fragmentation: Habitat fragmentation refers to the process where large, continuous habitats are divided into smaller, isolated patches, often due to human activities like urban development, agriculture, and road construction. This division can disrupt ecosystems and threaten the survival of species by reducing their living space and creating barriers to movement, which is significant for understanding community dynamics, biodiversity loss, and conservation efforts.
Host: A host is an organism that provides resources or a habitat to another organism, often in a symbiotic relationship. The host can be affected positively, negatively, or neutrally by this interaction.
Interspecific competition: Interspecific competition refers to the struggle between individuals of different species for the same limited resources, such as food, space, or light. This form of competition can significantly influence community structure and dynamics, impacting species diversity and population sizes. Interspecific competition often leads to competitive exclusion or resource partitioning, shaping the ecological interactions between different species in a community.
Keystone species: A keystone species is an organism that has a disproportionately large impact on its environment relative to its abundance. The removal of a keystone species can cause significant changes in the structure and diversity of an ecosystem.
Keystone Species: A keystone species is an organism that has a disproportionately large effect on its environment relative to its abundance. This means that their presence or absence can significantly influence the structure and dynamics of the entire ecosystem, making them crucial for maintaining biodiversity and ecological balance.
Lotka-Volterra model: The Lotka-Volterra model is a mathematical representation of the dynamics between predator and prey populations, illustrating how their populations fluctuate over time. This model shows that as prey populations increase, predator populations also grow, but as predators consume more prey, the prey population decreases, leading to a cyclical pattern of population dynamics. It highlights the interdependence of species within a community and helps in understanding community structure and interactions.
Mimicry: Mimicry is a biological phenomenon where one species evolves to resemble another species, gaining an advantage in survival and reproduction. This resemblance can be visual, auditory, or even chemical, allowing the mimic to deceive predators or competitors. Mimicry plays a crucial role in community interactions, influencing predator-prey dynamics and species coexistence.
Müllerian mimicry: Müllerian mimicry is an evolutionary phenomenon where two or more harmful species evolve to resemble each other. This mutual resemblance enhances predator avoidance and reinforces the learned aversion of predators.
Mutualism: Mutualism is a type of symbiotic relationship where both species involved benefit from the interaction. It enhances the survival, reproduction, and overall fitness of both organisms.
Mutualism: Mutualism is a type of symbiotic relationship where both species involved benefit from the interaction. This interaction can enhance the survival and reproduction of both partners, leading to increased fitness for each organism. Mutualistic relationships can be seen across various ecosystems, where organisms rely on one another for resources like food, shelter, or pollination.
Niche differentiation: Niche differentiation refers to the process by which competing species evolve to utilize different resources or habitats, reducing competition and allowing for coexistence. This concept emphasizes the role of species adapting their behaviors, diets, or habitats to minimize overlap with others, thereby promoting biodiversity within communities. By reducing direct competition for resources, niche differentiation helps stabilize ecological interactions and supports the overall health of ecosystems.
Parasite: A parasite is an organism that lives on or inside a host organism and benefits at the host’s expense. Parasites often cause harm to their hosts, ranging from mild discomfort to severe disease or death.
Parasitism: Parasitism is a symbiotic relationship where one organism (the parasite) benefits at the expense of another (the host). In fungi, this often involves the fungi deriving nutrients from the host, causing harm to it.
Parasitism: Parasitism is a type of symbiotic relationship where one organism, the parasite, benefits at the expense of another organism, the host. This interaction can significantly influence ecological dynamics, population structures, and community interactions, as the health and survival of hosts can be compromised by parasitic organisms.
Pioneer species: Pioneer species are the first organisms to colonize a barren or disturbed environment, initiating an ecological succession. They are typically hardy and adaptable, facilitating the establishment of subsequent species by modifying the habitat.
Pioneer Species: Pioneer species are the first organisms to colonize previously disrupted or damaged ecosystems, initiating the process of ecological succession. These species are crucial because they prepare the environment for subsequent organisms by modifying the habitat, such as improving soil quality and creating shelter, which allows for greater biodiversity to develop over time.
Predator-prey relationships: Predator-prey relationships refer to the interactions between two species, where one organism, the predator, hunts and consumes another organism, the prey. These relationships are crucial for maintaining ecological balance, influencing population dynamics, and driving evolutionary adaptations in both predators and prey. The interplay between these two groups also affects community structure and biodiversity within an ecosystem.
Primary succession: Primary succession is the ecological process that occurs in lifeless areas where no soil exists, such as after a volcanic eruption or glacial retreat, leading to the gradual establishment of a biological community. This process involves the colonization of pioneer species, which prepare the environment for more complex organisms over time, ultimately resulting in a stable ecosystem. Understanding primary succession helps highlight how ecosystems develop and recover from disturbances.
Relative species abundance: Relative species abundance measures the proportion of each species within an ecosystem. It provides insight into the diversity and health of a community by indicating how common or rare each species is relative to others.
Resource partitioning: Resource partitioning is the process through which different species in a community utilize resources in different ways or at different times, reducing competition and allowing coexistence. This phenomenon often leads to a more stable ecosystem where multiple species can thrive by dividing available resources, such as food, light, or habitat. Resource partitioning is crucial for understanding how communities function and how populations can grow sustainably within environmental limits.
Secondary succession: Secondary succession is the ecological process that occurs when a disturbance disrupts an existing community but leaves the soil intact, allowing for the recovery and re-establishment of ecosystems. This process can happen after events like fires, floods, or human activities that clear vegetation. Secondary succession typically progresses faster than primary succession because the soil already contains nutrients and seeds from previous vegetation.
Species interactions: Species interactions refer to the various ways in which different species within a community engage with one another, influencing each other's abundance, distribution, and evolution. These interactions can be positive, negative, or neutral and include a variety of relationships such as predation, competition, mutualism, and commensalism. Understanding these interactions is crucial for grasping how ecosystems function and how species coexist within their environments.
Symbioses: Symbioses are interactions between two different organisms living in close physical association, often to the benefit of both. These relationships can be mutualistic, commensalistic, or parasitic.
Symbiosis: Symbiosis refers to the close and long-term interaction between two different biological species. This relationship can be beneficial, harmful, or neutral for one or both parties involved and plays a crucial role in the dynamics of ecosystems, influencing everything from nutrient cycling to community structure.
Trophic cascades: Trophic cascades are ecological phenomena that occur when changes in the population of one species, often a predator, have a ripple effect throughout the entire food web, influencing the abundance and distribution of multiple other species. These cascades can significantly alter community structure and ecosystem dynamics, highlighting the interconnectedness of organisms within an environment. Understanding trophic cascades is crucial for grasping how ecosystems function and how human activities can disrupt these delicate balances.