Predator-Prey Dynamics, Symbiosis, and Ecosystem Interactions
Predator and Prey Relationships
Predators possess traits or skills that help them catch and kill their prey. Different types of predators have different skills and traits. For example, a cheetah uses its speed to catch prey. On the other hand, tigers have colors that let them blend with the environment so that prey cannot see them easily.
Prey Defenses
Prey generally have some way to protect themselves from being eaten. Different types of organisms protect themselves in different ways:
1. Running Away
When a rabbit is in danger, it runs.
2. Traveling in Groups
Some animals, such as musk oxen, travel in herds, or groups. Many fish, such as anchovies, travel in schools. All the animals in these groups can help one another by watching for predators.
3. Warning Colors
Some organisms have bright colors that act as a warning. The colors warn predators that the prey might be poisonous. A brightly colored fire salamander, for example, sprays a poison that burns.
The colors are: Black, red, blue, yellow, orange.
4. Camouflage
Some organisms can hide from predators by blending in with the background. This is called camouflage. A rabbit’s natural colors, for example, blend with shrubs so that it cannot be seen. Some animals may look like twigs, stone, or bark.
Symbiosis: Close Interactions Between Species
Some species have very close interactions with other species. A close association between two or more species is called symbiosis. Each individual in a symbiotic relationship may be helped, hurt, or not affected by another individual. Often, one species lives on or in another species. Most symbiotic relationships can be divided into three types: mutualism, commensalism, and parasitism.
Mutualism
When both individuals in a symbiotic relationship are helped, it is called mutualism. You can see mutualism in the relationship between a bee and a flower.
Commensalism
When one individual in a symbiotic relationship is helped but the other is not affected, this is called commensalism.
Parasitism
A symbiotic relationship in which one individual is hurt and the other is helped is called parasitism. The organism that is hurt is called the host.
How Do Organisms Interact?
Relationships between organisms change over time.
Carrying Capacity
The largest number of organisms that can live in an environment is called the carrying capacity. When a population grows beyond the carrying capacity, limiting elements will cause some individuals to leave the area or to die. As individuals die or leave, the population decreases.
The carrying capacity of an area can change if the amount of the limiting element changes. For example, the carrying capacity of an area will be higher in periods when more food is available.
Why Do Organisms Compete?
Competition happens when more than one individual or population tries to use the same resource. There may not be enough resources, such as food, water, shelter, or sunlight, for all the organisms in an environment. When one individual or population uses a resource, there is less for others to use.
How Do Organisms Interact in an Ecosystem?
Populations are made of individuals of the same species. Communities are made of different populations that interact. There are four main ways that individuals and populations affect one another in an ecosystem: in competition, as predator and prey, through symbiosis, and changes in organisms.
How Does the Environment Control Population Sizes?
Most living things have more offspring than will survive.
Populations cannot grow without stopping because the environment has only a certain amount of food, water, space, and other resources. A resource that keeps a population from growing forever is called a limiting element.
Food is often a limiting element in an ecosystem.
How Do Predators and Prey Interact?
Another way organisms interact is when one organism eats another to get energy. The organism that is eaten is called the prey. The organism that eats the prey is called the predator.