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Honors Biology
Table of Contents
Unit 18 Overview: Population and Community Ecology
18.1 Population Dynamics and Growth Models
18.2 Community Interactions and Succession
18.3 Biodiversity and Species Interactions

🐇honors biology review

18.2 Community Interactions and Succession

Citation:

Ecosystems are dynamic, constantly changing through succession and species interactions. From barren landscapes to thriving forests, communities evolve over time. Keystone species, facilitation, and resource partitioning shape these complex webs of life.

Community interactions drive ecosystem development and stability. Understanding these processes helps us grasp how nature recovers from disturbances and maintains biodiversity. It's all about species finding their niche and adapting to coexist in ever-changing environments.

Succession

Primary Succession

  • Occurs in areas where no soil or organisms existed before such as volcanic islands or areas covered by glaciers
  • Begins with pioneer species like lichen and moss that can grow on bare rock and break it down into soil
  • As soil develops, more complex plants like grasses and shrubs can grow, followed by trees
  • Over time, a climax community forms that remains stable until disrupted (old-growth forest)

Secondary Succession

  • Occurs in areas where soil remains but existing ecosystem has been removed by a disturbance like a wildfire, flood, or human activity (logging)
  • Pioneer species are often grasses and herbaceous plants that grow quickly in full sun
  • Progresses more rapidly than primary succession since soil is already present
  • Intermediate stages include fast-growing trees like aspen before returning to a climax community (mature oak-hickory forest)

Community Interactions

Keystone Species

  • Species that have a disproportionately large impact on the structure and function of their ecosystem relative to their abundance
  • Their removal drastically alters or destroys the ecosystem
  • Examples include sea otters in kelp forests that control sea urchin populations and beavers that create wetlands by damming streams

Ecological Facilitation

  • Occurs when one species makes the environment more favorable for another species, often by modifying the habitat
  • Nurse plants like shrubs in a desert provide shade and moisture that allows tree seedlings to establish
  • Legumes have symbiotic bacteria in their roots that fix atmospheric nitrogen into a form plants can use, facilitating the growth of other species

Ecological Communities

  • Consist of all the interacting populations of species living in the same place at the same time
  • Include both the biotic (living) and abiotic (non-living) components of the environment
  • Communities can be described by their species richness (number of species present) and species evenness (relative abundance of each species)
  • Boundaries between communities can be sharp (lake edge) or a gradual transition zone called an ecotone (grassland to forest)

Species Relationships

Niche and Competitive Exclusion

  • A niche refers to the role a species plays in the ecosystem and includes all the biotic and abiotic resources it needs to survive and reproduce
  • Includes the species' habitat, food sources, and interactions with other organisms
  • The competitive exclusion principle states that two species cannot occupy the same niche in the same place for very long
  • One species will be a better competitor and exclude the other species, driving it to extinction or forcing it to adapt to a different niche

Resource Partitioning

  • Occurs when species with similar resource needs evolve to specialize on different parts of the resource to avoid direct competition
  • Allows similar species to coexist in the same habitat
  • Examples include different species of warblers feeding in different parts of the same tree and anole lizards adapting to different perches and food sources in the Caribbean islands

Key Terms to Review (15)

Competitive exclusion: Competitive exclusion is a principle stating that two species competing for the same limited resources cannot coexist indefinitely. In other words, one species will outcompete the other, leading to the extinction or displacement of the less competitive species. This concept highlights the importance of resource availability and the dynamics of community interactions, illustrating how species interactions shape ecological communities over time.
Ecological facilitation: Ecological facilitation refers to the process where one species positively impacts the establishment, growth, or survival of another species in an ecosystem, often enhancing community structure and biodiversity. This interaction can occur through various mechanisms, such as providing habitat, altering nutrient availability, or modifying environmental conditions. Understanding ecological facilitation helps to shed light on the complex relationships that shape communities and influence ecological succession.
Species richness: Species richness refers to the number of different species present in a specific area or ecosystem. It is a crucial component of biodiversity, reflecting the variety of life forms that contribute to the overall health and resilience of ecosystems. Higher species richness often indicates a more stable ecosystem, as diverse species can fulfill various ecological roles, leading to increased productivity and better resistance to environmental changes.
Secondary succession: Secondary succession is the ecological process through which a community of organisms re-establishes itself after a disturbance that does not completely destroy the existing soil and organisms. This type of succession occurs in areas where a disturbance, such as fire, flooding, or human activity, has disrupted the ecosystem but left behind some remnants of the previous community, including soil, seeds, and other biological materials. The process typically progresses faster than primary succession because it begins with pre-existing soil and some life forms.
Ecological Stability: Ecological stability refers to the ability of an ecosystem to maintain its structure, function, and resilience over time despite disturbances or changes in environmental conditions. This concept encompasses how well a community can withstand stress and continue to thrive, with a focus on species diversity, interspecies interactions, and the processes that govern ecological succession.
Primary Succession: Primary succession is the ecological process that occurs in an area where no soil or organic matter exists, leading to the gradual establishment of a biological community. This process often begins on bare rock surfaces or other lifeless substrates following events like volcanic eruptions or glacial retreats, allowing for the development of soil and eventually a complex ecosystem. Understanding primary succession helps illustrate how life can colonize and transform environments over time.
Ecological Communities: Ecological communities refer to groups of interacting species that coexist in a specific environment, sharing resources and impacting each other's populations. These communities are dynamic systems shaped by the interactions between organisms, including competition, predation, and symbiosis, and can evolve over time through processes such as succession. Understanding these interactions is essential for grasping how ecosystems function and maintain biodiversity.
Species evenness: Species evenness is a measure of the relative abundance of different species in a given ecological community. It describes how evenly individuals are distributed among the various species present, which can impact the stability and resilience of ecosystems. High species evenness means that species are present in similar numbers, while low evenness indicates that a few species dominate the community.
Climax community: A climax community is a stable and mature ecological community that has reached a state of equilibrium, where species composition remains relatively unchanged over time. This community is characterized by a complex structure and high biodiversity, which allows it to sustain itself through various environmental changes. The concept is essential for understanding ecological succession and the interactions among different species within an ecosystem.
Pioneer species: Pioneer species are the first organisms to colonize previously disrupted or damaged ecosystems, initiating the process of ecological succession. These hardy species are crucial for transforming barren environments into more complex ecosystems by improving soil quality and creating conditions suitable for other organisms to thrive.
Ecotone: An ecotone is a transition area between two different ecosystems or communities, where species from both ecosystems can coexist and interact. This unique zone often exhibits increased biodiversity due to the overlapping species and can lead to dynamic interactions among organisms. Ecotones play a critical role in ecological succession, as they can facilitate the movement of species and the exchange of genetic material between adjacent ecosystems.
Resource partitioning: Resource partitioning is a process through which species in a community utilize different resources or occupy different ecological niches to minimize competition. This allows multiple species to coexist in the same environment by reducing overlap in resource use, promoting biodiversity and stability within ecosystems.
Biodiversity: Biodiversity refers to the variety of life on Earth, encompassing the different species of plants, animals, fungi, and microorganisms, as well as the ecosystems they form and the genetic variations within these species. This diversity is crucial for ecosystem stability, resilience, and overall health, playing a vital role in the interactions among organisms and their environment. Biodiversity influences how ecosystems function and recover from disturbances, thus connecting it to both biotic and abiotic factors in ecological studies.
Keystone Species: A keystone species is a species that has a disproportionately large impact on its environment relative to its abundance. Its presence or absence can significantly affect the structure and diversity of the entire ecosystem, influencing many other organisms and their interactions within the habitat. Keystone species often play crucial roles in maintaining the balance of the community, making them essential for ecological stability.
Niche: A niche refers to the specific role or function of an organism within its environment, including how it obtains resources, interacts with other organisms, and contributes to the ecosystem. It encompasses both the physical habitat an organism occupies and its position in the food web. The concept of a niche highlights the unique adaptations and behaviors that allow different species to coexist and thrive in various ecological contexts.