Interactive note taking-Interactions Within Populations

Interactions Within Populations

We have learned that the Earth is filled with ecosystems.  An ecosystem is defined as the living organisms within a specific area and the physical environment or abiotic factors that support them.  Scientists divide ecosystems further into communities. A community consists of the living or biotic factors in an ecosystem.  This would include the different plants and animals that interact with each other. 

Communities are broken down further into populations.  A population is a group of organisms of the same species that live in a particular area.  Organisms that are the same species are so similar they can mate and produce offspring that can also mate and produce offspring. 

Some populations establish a social order or hierarchy where the size, hunting ability, or reproductive capabilities of one or more members places them in positions of dominance over the rest of the population.  With the establishment of a social order, the dominant members are most likely to breed and get first choice of the available food resources.   Although the type of social order may differ from population to population, the establishment of a social order makes sure that labor and resources are adequately shared within a population of organisms.

In an ecosystem, basic resources are in limited supply.  Because of this, members of plant and animal populations are often in competition with each other. The competition for resources within a population can be great because the basic resources they need are the same.  Because of the limited number of resources, only a certain number of organisms can survive in a particular place at one time. If a population grows too large, some organisms may die.  Others will leave that particular population, if they can, in search of a location with more resources.  The supply of resources in an area ultimately controls the growth and size of a population.

Members of an animal population compete for such limited resources as food, water, shelter, mates, and territory. Some animals such as monkeys, deer, and wolves will establish or claim a territory that contains the basic resources they need.  This claiming can be done with smell, sound, or touch.  Wolves will mark their territory with urine, monkeys will scream, and deer will lock horns in battle.  Bird populations often establish territories to protect their nesting sites.  Establishing a territorial imperative makes sure that the members of a population have the resources they need to survive.

The members of a plant population also compete for limited resources.  Some of these resources include water, sunlight, soil nutrients, and space.  Competition between the members of a plant population can be due to their inability to move in search of the resources they need.

Not all interactions between the members of a population involve competition.  Organisms also cooperate, or work with each other to meet basic needs.

Some populations cooperate by establishing a social order or hierarchy that will help them meet the needs of all of their members.  For example, the members of an ant population are divided into groups or castes that are responsible for carrying out specific jobs.  Some ants take care of their queen, while others search for food or defend the colony.   

Other populations cooperate in specific ways to meet specific needs such as food, protection, caring for young, and shelter. Predators, such as wolves, cooperate by hunting for food in packs.  They need the help of other members of the population to catch difficult or large prey.  Other animals living in herds, packs, or prides are engaged in territorial cooperation.  This kind of cooperation offers protection by safety in numbers.  For example, a herd of Musk oxen will cooperate to protect their young.  When threatened by a predator, musk oxen form a circle around their young with their horns pointing out.

Another form of cooperation is found in animal populations that share the rearing of young.  For instance, meerkats in southern Africa take turns “babysitting” at the den, hunting for food, and nursing the youngsters.  Apes, monkeys, and lions are other examples of animal populations that cooperate to care for their young.  Other populations will cooperate for shelter.  Good examples include bee, ant, and termite colonies. These populations work together to construct and protect their homes.