Community Ecology

How species interact with each other and their environment.

Polar bear
Fleas and ticks
Remora fish and sharks
The 1988 Yellowstone forest fire

Definition of Community Ecology

Community ecology is the study of how species interact with each other and their environment. It seeks to understand how populations of different species are distributed, why they coexist or compete, and what factors influence their interactions. A community in ecology is defined as a group of two or more different species living in the same space at the same time. For example, a forest community could be made up of the various tree species growing there, as well as other plants, fungi, invertebrates, squirrels, foxes and more. Community ecologists seek to understand the factors which structure these communities and influence biodiversity and relative abundances – including abiotic factors and interspecies relationships.

Community ecologists use a variety of methods to answer questions about the relationships in communities, such as field observations, experiments in controlled environments, mathematical models, and computer simulations. By studying communities at multiple scales—from individual organisms to entire ecosystems—ecologists can gain insight into the complex dynamics that shape them. Through this research we can better understand how human activities affect biodiversity and ecosystem functioning. Ultimately, community ecology helps us make informed decisions about conservation strategies that will protect our planet’s fragile ecosystems for future generations.

Species Interactions

Species interactions are the ways in which different species interact with each other within an ecosystem. These interactions can have a significant influence on the structure and functioning of a community, as they determine how resources are used and distributed among its members.

Competition is one type of interspecies interaction, where two or more species compete for limited resources such as food, water, or space. Mutualism occurs when two species benefit from their relationship; for example, some plants rely on pollinators to spread their pollen while providing nectar in return. Predation involves one organism consuming another; this could be a carnivore hunting prey animals or herbivores grazing on vegetation. Herbivory is similar but refers specifically to plant-eating animals like deer and rabbits that feed off vegetation, generally without killing it. Finally, parasitism describes relationships between organisms where one benefits at the expense of the other. Parasites live off hosts by feeding on them or living inside them without causing death. All these types of species interactions play an important role in shaping communities and maintaining biodiversity across ecosystems worldwide.

Interspecific Competition

Interspecific competition is a type of species interaction in which two or more organisms of different species compete for limited resources. This is distinct from intraspecific competition, which involves two or more organisms of the same species competing for resources. For example, different tree species may compete for light and nutrients in a forest ecosystem.

Interspecific competition can have significant impacts on both individual species and entire communities. It can lead to decreased growth rates, reduced reproductive success, and even extinction if one organism outcompetes another for essential resources. Additionally, competition among multiple species can alter community structure by changing the abundance of certain populations or creating new niches that are filled by other organisms. Understanding how interspecific competition affects ecosystems is an important part of ecology research as it helps us better manage our environment and protect biodiversity worldwide.



Predation is an important interaction between species in which one organism, the predator, hunts and consumes another organism, the prey. Predators can be solitary hunters such as polar bears or group hunters such as orcas, who often work together to herd fish before stunning them by striking their tails. Not all predators are animals – carnivorous plants, such as the Venus flytrap which captures insects with specialized leaves, are also predators.

Predation has a significant impact on communities by controlling population sizes and influencing species interactions. For instance, predation can reduce intraspecific competition in prey species by removing individuals from a population: decreasing the pressure on resources for the surviving members. By preying on dominant species, predators can also allow other species to thrive by reducing the competition between species. Additionally, predation can create new niches that are filled by other organisms when certain populations become scarce due to predation pressure. Understanding how predation affects ecosystems is essential for conservation efforts and managing our environment responsibly.



Herbivory is the process of an organism consuming plants or parts of plants. This can range from grazing on grasses and shrubs to consuming flowers, fruits, roots, and seeds. Herbivores include a wide variety of animals such as deer, elephants, koalas, and insects like caterpillars. Plants have evolved various defenses to protect themselves from herbivores; these can be physical barriers such as thorns or chemical deterrents like toxins in leaves. In response to these defenses, herbivores have developed strategies for avoiding them while still obtaining nutrition from the plants they consume – such as long tongues and resistance to toxins. Koalas, for example, have evolved to rapidly process the toxins in eucalyptus leaves – allowing them to consume large quantities each day.


Herbivory has a significant impact on communities by influencing species distributions and population sizes of both predators and prey. For example, when sea urchins feed on kelp forests they reduce their abundance which in turn affects other organisms that rely on those habitats for food or shelter. Similarly, large grazers like zebras shape savanna ecosystems by controlling vegetation growth through selective feeding patterns; this creates open areas where smaller grazers can thrive alongside larger predators who hunt them for food.


Parasitism is a type of species interaction in which one organism, the parasite, lives on or within another organism, the host. Unlike predation, where one organism consumes another for food and energy, parasitism involves an intimate relationship between two organisms. This relationship benefits only the parasite. Parasites can be either ectoparasites (living outside their hosts) or endoparasites (living inside their hosts). Examples of ectoparasites include fleas and ticks; examples of endoparasites include tapeworms and roundworms.

Parasitism has significant impacts on communities by affecting both the parasites’ hosts as well as other species in the ecosystem. For example, when parasites feed off their host they reduce its ability to survive and reproduce. This can lead to population declines in prey species which may have cascading effects throughout an entire community. Additionally, some parasites alter behavior or physiology of their hosts which can affect interactions with other species such as competition for resources or predator-prey dynamics. By understanding how parasitism affects communities we are better able to manage our environment responsibly and conserve biodiversity worldwide.


Mutualism is an important type of species interaction in which two organisms of different species benefit from their relationship. Examples of mutualistic relationships include the remora fish and sharks, where the remora attaches itself to the shark’s body and feeds on scraps left behind by its host while providing protection against parasites. Other examples include ants that protect plants from herbivores in exchange for food or shelter, as well as bacteria living inside animals that help them digest food.

Mutualism can have a significant impact on communities by influencing species distributions and population sizes. For example, when two species form a mutualistic relationship they may become more abundant than if they were alone; this could lead to increased competition with other species for resources such as food or space. Additionally, some mutualisms are so strong that one organism cannot survive without the other; this can create an imbalance in ecosystems if one partner becomes extinct due to human interference or environmental changes. Understanding how mutualism affects communities is essential for conservation efforts and managing our environment responsibly.

Keystone species

A keystone species is an organism that has a disproportionately large effect on its environment relative to its abundance. These species play a critical role in maintaining the structure and function of ecosystems, often acting as “architects” or “engineers” by creating habitats for other organisms. Beavers are one example of a keystone species; they build dams which create ponds and wetlands, providing habitat for fish, amphibians, birds, and mammals. Additionally, beaver dams can reduce flooding downstream by slowing the flow of water during heavy rains. Other examples include sea otters in kelp forests and wolves in grasslands; both help maintain healthy populations of their prey while also influencing vegetation growth patterns. Keystone species have been shown to increase biodiversity within an ecosystem by providing resources for many different types of organisms. As such, they are essential components of healthy ecosystems and must be protected from human interference or environmental changes if we want to ensure their continued existence and the healthy ecosystems they maintain.


Ecological succession is the process by which a community of organisms changes over time. It begins with pioneer species, which are adapted to colonize and thrive in newly available habitats. These species create conditions that allow other species to move in and establish themselves, leading to a more diverse and complex community. Over time, these communities can reach a climax state where they remain relatively stable until disturbed again.

Primary succession occurs when an area has been completely devoid of life due to extreme environmental conditions such as volcanic eruptions or glacial retreats; secondary succession takes place after disturbances such as fires or floods have removed some but not all of the existing vegetation from an area.

In both cases, successional processes lead to increased biodiversity and complexity within the ecosystem over time. As different species interact with each other and their environment, they form new niches for other organisms while also influencing abiotic factors like soil composition and water availability.

Understanding how ecological succession works is essential for managing our environment responsibly so that we can maintain healthy ecosystems into the future.

Disturbance ecology

Ecological disturbances are events that cause significant changes to an ecosystem, such as fires, floods, hurricanes, and volcanic eruptions. These disturbances can have a major impact on the species composition of a community by removing existing organisms or creating new habitats for others. Disturbance ecology is the study of how these events affect communities and ecosystems over time.

The 1988 Yellowstone forest fire is an example of how ecological disturbance can shape an environment. The fire burned more than 3000 square kilometers of land, killing thousands of trees and hundreds of large mammals. However, it also created new opportunities for other species to move into the area. Within two years of the fire there was already evidence of increased biodiversity in some areas due to colonization by pioneer species like lodgepole pine and Douglas fir. This illustrates how even catastrophic events can lead to positive outcomes if given enough time for recovery processes to take place. By studying disturbance ecology we can better understand how our actions may influence ecosystems both positively and negatively over time.


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