Communities of animals or plants experience a great level of complexity. While it is true that animals and plants compete among themselves for space and resources, they also depend on each other to ensure a stable community. Let’s go ahead and explore some of these complexities in a community, some examples, and more.
Definition of Community in Biology
A community consists of populations (usually 2 or more) of different species interacting with each other in the same habitat.
You may remember that a population is a group of organisms of the same species living in the same area.
Populations in a community may compete for resources with each other, or even within their own population. This is called competition.
Plants often compete for water, light, space or minerals.
Animals often compete for food and water, space, and mates.
We will explore this below.
Examples of Communities in Biology
Having explored the definition of a community in the above section, let's go on and explore some examples of different communities. Remember, a community refers only to biotic factors, and a population is a group of organisms of the same species living in the same area.
It's important for us to understand that when referring to populations, we are talking about members of the same species. However, when we discuss communities, we are essentially adding up all of these different populations that can be found in the same area.
Let's look at an example to understand what a community is.
Let's use our homes and families as an example of a community. If you're sitting at home now, think about who else is at home with you. Any biotic factors inside of your house count.
So, let's think! You may think about your mother, father, siblings or even grandparents or any other relatives that are in your home at the moment, and these would all be correct. These are all members of the same species in the same area - so we could describe them as a population.
What about your pets? Do you have a dog? Or maybe several dogs? Or fish? Or maybe a cat? These are all different species from each other but are found in the same location.
Finally, let's think about some populations that you may not have considered. Think about some of the different spiders and insects that you sometimes see around your house, these also count as biotic factors that have their own populations!
When we add up these different populations that may be found inside your home, we get a community!
Abiotic factors do not contribute to a community, instead, they play a role in forming the definition of an ecosystem. Take a look below!
A Community's Biotic and Abiotic Factors
In order to understand the difference between community and ecosystem, we need to understand a few other definitions. Firstly, we need to understand the difference between biotic and abiotic factors.
Biotic factors are living things, or things that were once living. This includes animals, plants, bacteria or dead and decomposing materials of these organisms.
Abiotic factors are non-living factors. This includes wind speed, temperature, light intensity and more.
Fig. 1 - Biotic and abiotic factors
Abiotic and biotic factors interact with each other, and should not be considered in isolation.
Now that we understand the difference between abiotic and biotic factors, we need to understand another term - population.
A population is a group of organisms of the same species that live in the same area.
Community vs Ecosystem
Community and ecosystem are terms that are often used interchangeably. However, they do not mean the same thing! Having understood the difference between an abiotic factor and a biotic factor, we can now move on to discuss the difference between a community and an ecosystem.
A community is the sum of all of the biotic factors in one area. This includes all of the different species in one area. Plants, animals, bacteria and any other living group make up a community.
An ecosystem is the sum of both the biotic and abiotic factors in a particular area and how they interact with each other. This includes animals and plants but also how wind speed and temperature affect these organisms.
Let's consider an example that allows us to highlight the difference between an ecosystem and a community.
Let's take a local park as an example. Imagine you are sitting in a park with some friends. What you can see around you? There may be bugs crawling around the floor, dogs chasing after balls that their owners have thrown, and birds flying from one tree to another. As you're sitting in the sun, you notice that you're getting quite warm, so you decide to go cool off in the stream nearby.
Can you think about which factors would count as biotic and abiotic factors in the paragraph above? How about the difference between a community and an ecosystem based on this paragraph?
The dogs, birds and bugs, as well as yourself and your friends, are all living organisms and are therefore biotic factors. When we add together all of these different populations, we get the community within that area. When we take this community and add in the heat from the sun, and the nearby stream as well as any other abiotic factors we now have an ecosystem!
Try to do the same thing with whatever area you are currently sitting in! Can you see out of your window? What abiotic and biotic factors can you spot?
Characteristics of a Community
Within a community, there are lots of different characteristics. As there are lots of different species, there are many interactions between these different species. Similarly, there are many complex dynamics between members of the same species. These interactions include both competition and dependence.
Competition in Animals
Factors such as food, mating, space and other resources all lead to competition among members of the same species or between members of different species.
Food
Every living organism requires some form of food; it provides them with the energy and raw material to perform crucial life processes, such as respiration, growth and reproduction. Without completing these life processes, the animals will die. The competition for food can therefore be very aggressive in some communities. Some animals may fight each other for the same food, while some animals may compete by outsmarting others by working around a food shortage.
This type of competition is mostly intraspecific (between animals of the same species) because they occupy the exact same niche (role in the ecosystem). However interspecific competition (between animals of different species) also occurs if the animals’ niches happen to overlap.
Mating
Competition for mates can also become very fierce. Animals must mate in order to produce offspring and pass on their genes. Normally, males compete against other males for the right to mate with a female. They may fight each other, as seen in the annual rut of the deer, during the mating season (figure 2).
Male deer will lock horns and establish their dominance to try and ‘win over' the female. This type of competition is always intraspecific because only members of the same species can breed to produce fertile offspring.
Figure 2. Red deer ready to rut.
Space
The space, or territories, of an animal includes all of the resources they need to survive and flourish.
Have you ever noticed how territorial a cat can become when another cat enters its garden? This is because a cat’s natural instinct is to defend its territory.
Animals have different adaptations that make them better at competing for resources and mates. These adaptations can be either physiological, anatomical or behavioural. Animals that deliberately hunt at night to give themselves an advantage over their prey, show a behavioural adaptation. Physiological adaptations include different ways that animals communicate and process such as hibernation too. Anatomical adaptations include the shape of a rabbit's legs or the shape of an eagle's claws.
Competition in Plants
Plants compete with each other in different ways than animals compete with each other. Factors such as light availability, soil quality, water and resource availability and again, space all lead to this competition .
Light
As you may already know, all plants and algae require light in order to perform photosynthesis. Since sunlight is crucial for photosynthesis, plants compete for sunlight by trying to outgrow other nearby plants.
Water and Minerals From the Soil
Soil holds the water and minerals plants need to survive. Plants will therefore compete with each other to obtain a regular supply.
Water is an important reactant in photosynthesis. Large trees lose huge amounts of water every day, therefore they need to recover this lost water through absorption from the soil. These trees have wide-ranging and thick roots to increase surface area for water absorption.
Minerals, such as nitrogen, phosphorous and magnesium, are essential for the healthy functioning of plants. Without some of these minerals, plants can develop diseases or may have growth issues. This is the only way to obtain minerals for most plants. However, some plants like Venus flytraps, have evolved mechanisms to capture and consume insects. This puts them at an advantage over other plants in the community who can only obtain minerals through the soil.
Space
Plants also compete for space. They grow best with some space between each other, because this avoids their leaves being shaded by other plants which could affect their photosynthesis potential. When old trees die, the younger trees are quick to compete for the available space.
In a similar way to how animals have different adaptations, plants also have adaptations that improve their ability to compete with other plants for resources and light. An example of an adaptation that a plant may have could be having a shallow extensive network of roots to maximise water absorption. Another adaptation could be when trees grow tall in order to get above the canopy and maximise their light absorption.
What is interdependence?
While animals and plants compete with each other to survive, they are also dependent on each other.
Populations of different species in a community are often dependent on each other. This is known as interdependence.
When the number of one species is impacted, there will be knock-on effects on the other species in the food chain.
Take a look at this simple food chain;
Plant → Mouse → Snake
If the snakes in the above food chain were to decrease in population, the mice would have fewer predators, so we could expect to see an increase in the number of mice. Now, with an increase in the population of mice, the number of plants in the area would decrease because all of the mice would be eating them.
Communities - Key takeaways
A community consists of populations (usually 2 or more) of different species interacting with each other in the same habitat
Interdependence is when populations in a community are often dependent on each other
Animals compete for food, mates and space.
Plants compete for light, water, minerals and space.
References
- Figure 2: Deer rut (https://commons.wikimedia.org/wiki/File:Phoenix_Park_Deer_Rut_2015.jpg) by Irish Wildlife Trust Dublin Branch. Licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en).
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