When you think of the word 'community' you may imagine your neighborhood or perhaps even the town you live in. Humans often use the word to describe certain groups based on various demographic, lifestyle, and sociopolitical factors. In the following, we will look at the study of communities at an ecological level, known as community ecology. We will look at the patterns of structure within ecological communities, as well as the community ecology theory and some examples.
Definition of community ecology
The definition of community ecology, also known as synecology, is an ecological field of study which involves populations of different species at a community level, their interactions, and how the biotic and abiotic factors present affect them. Some of the factors involved in the study of community ecology include mutualism, predation, the physical constraints of the environment, population size, demographics, and much more.
A community consists of populations of at least two (but usually many) different species that exist within the same environment and interact with each other.
The populations of each species occupy different ecological niches in the community.
A species' niche is the portion of the environment in which that species has evolved to specialize.
Some species are more specialized, while others are more generalized, but all occupy a specific niche. The partitioning of these niches helps to minimize the level of interspecies competition and conflict and promotes coexistence within the community.
The number of available niches within the community dictates its level of biodiversity. A community with more niches (e.g., tropical rainforest) is going to have higher levels of biodiversity than a community with fewer niches (e.g., arctic tundra). Occasionally, closely related species existing within the same community may compete for the same or similar resources.
These species are referred to as being part of a guild.
The community also has specific trophic levels.
A trophic level refers to the location of a species on the food chain.
It is best to look at the trophic levels as a pyramid of energy transfer, with apex predators (quaternary or tertiary consumers) (e.g., big cats, large crocodilians, etc.) at the top, followed by omnivores and smaller carnivores (secondary consumers), herbivores (primary consumers), plants (producers), and decomposers.
As you may notice, energy is passed between these levels- decomposers allow plants to grow in the soil, herbivores eat the plants, and predators prey upon herbivores.
Within a community, some species have a larger impact than others.
Keystone species, for example, greatly impact species on lower trophic levels (usually through predation). Keystone species are often apex predators, such as the Bengal tiger (Panthera tigris) and the saltwater crocodile (Crocodylus porosus).
If these keystone species are extirpated from the area, as is often the case where human-wildlife conflict occurs, the populations of prey species on the lower trophic levels tend to explode. This overpopulation often results in the overconsumption of plant species, thus reducing the resources available for other species. Another group that has a large impact on the community are foundation species, which are often producers (plants) but can potentially be present at any trophic level.
Figure 2: The Bengal tiger is an example of a keystone species
Community ecology theory
The community ecology theory suggests that the variability in environmental factors plays a vital part in the coexistence between different species. Sometimes, this can result in opportunities for invading species to occupy specific niches if the resident species have different responses to the environmental factors involved.
This is particularly important in regard to invasive species, which may be able to become established in certain communities if they are able to occupy specific niches already occupied by native species that have different responses to spatiotemporal variations in the environment.
Population and community ecology
What is population and community ecology? A population is essentially a subunit of a species.
A population is a group of individuals of a particular species residing within a specific area, which is part of a larger community of different species.
Population ecology typically refers to the study of this single species population, as opposed to community ecology, which takes into account all species populations present within a community. Community and population are different levels of ecological organization, with the largest being the biosphere and the smallest being the individual.
The levels of ecological organization, in order from largest to smallest, are the biosphere, biome, ecosystem, community, population, and individual. Each higher level of organization contains the lower levels (e.g., ecosystems consist of many communities, while communities contain many populations of individuals).
Community ecology example
A fine example of a biological community would be the Pantanal wetland, found in western Brazil and eastern Bolivia. The Pantanal community consists of a wide variety of animal and plant species interacting and impacting each other. The yacare caiman (Caiman yacare) and the giant river otter (Pteronura brasiliensis) prey upon piranha, while the jaguar (Panthera onca) preys upon the caiman and numerous other species. The capybara (Hydrochoerus hydrochaeris) and the South American tapir (Tapirus terrestris) feed upon a variety of plant species and the piranha (Serrasalmidae) feed upon carrion and small animals.
These species are all members of the same biological community.
The biologist who studies these species and their various interactions within the Pantanal is working in the field of community ecology.
For example, a biologist may look at how the feeding habits of the caiman, giant river otter, and jaguar impact the population densities of common prey species such as the capybara and the marsh deer (Blastocerus dichotomus) specifically within the Pantanal wetlands.
Patterns of structure in community ecology
Communities in ecosystems are constantly experiencing disturbances that cause structural changes. These disturbances can come in the form of the arrival of new species, natural disasters (such as wildfires), and more. This process of constant disturbances and their resulting structural changes to species and habitats over time is known as ecological succession. There are two kinds of ecological succession: primary and secondary.
Primary Succession
Primary succession occurs when a previously lifeless, non-existent, or obscured habitat is colonized by species for the first time.
The first organisms to colonize this habitat are known as pioneer species. This pioneer species represents the first community and, over time, the community increases in complexity as biodiversity grows due to the arrival of more species.
Some ways in which primary succession can occur would be following natural disasters, such as volcanic eruptions, landslides, or soil erosion during flooding which all create or reveal new habitat that was not previously present. Primary succession can also be instigated by humans, through the abandonment of structures, thus allowing for the colonization of wildlife.
Secondary Succession
Secondary succession occurs when some ecological disturbance causes a habitat that was colonized by organisms previously to have much of its animal and plant life disappear, eventually resulting in the recolonization of the habitat.
Causes of secondary succession can include natural disasters, such as wildfires, which may eradicate many species or cause them to escape to other areas, and anthropogenic factors, such as agricultural development in habitat.
The key difference between primary and secondary succession is that, in secondary succession, life was previously present in the area and the habitat will eventually be recolonized, rather than being colonized for the first time.
During ecological succession, these communities are often subjected to stratification due to environmental gradients in abiotic factors, such as sunlight and air temperature. This stratification can be horizontal or vertical.
For example, in tropical rainforests (e.g., the Amazon) a vertical strata exists, with the tallest trees occupying the forest canopy and receiving the most sunlight, followed by smaller trees, bushes/shrubs, and, finally, plants closer to the forest floor.
This vertical strata has an impact on wildlife distribution, within certain species specializing in specific strata (e.g., some insect species may specialize in remaining on the forest floor, while monkeys may specialize in spending much of their time in the forest canopy).
Horizontal strata can be found in mountain ranges, with differences between slopes (e.g., eastern slope vs. western slope).
Community Ecology - Key takeaways
- Community ecology is an ecological field of study which involves populations of different interacting species at a community level.
- A community consists of populations of different species that exist within the same environment and influence each other, while a population is a group of individuals of a particular species residing within a specific area.
- Ecological succession is the process of constant disturbances and their resulting structural changes to species and habitat over time.
- Primary succession occurs when new habitat is colonized by species for the first time. Secondary succession occurs when a disturbance causes habitat that was colonized to become empty, eventually resulting in recolonization.
References
- Figure 2: Bengal Tiger (https://commons.wikimedia.org/wiki/File:Bengal_tiger_(Panthera_tigris_tigris)_female.jpg) by Sharp Photography (https://www.sharpphotography.co.uk). Licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en).
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