1. ENVIRONMENTAL SCIENCE
Chapter 8 Understanding Populations
8.2 How Species Interact With Each Other

2. 8.2 How Species Interact With Each Other Objectives
Explain the difference between niche and habitat.
Give examples of parts of a niche.
Describe the five major types of interactions between species.
Explain the difference between parasitism and predation.
Explain how symbiotic relationships may evolve.

3. Introduction
In order to understand a species, it is best to study it in its natural environment.
The interactions between species in the natural environment are often complex and cannot be replicated exactly in an artificial habitat.

4. An Organism’s Niche
A niche is the specific role of a species in an ecosystem.
A niche can include the environmental factors necessary for survival of that species, the species’ home, and all of the species’ interactions with other organisms.
A habitat is simply a location and type of factors in that location.
A niche involves the habitat plus interactions and behaviors characteristic of the species.

5. An Organism’s Niche
A niche can also be described as the functional role, or “job” of a species in an ecosystem.
For example, the bison is the large grazer on the plains of North America and the kangaroo is the large grazer in the grasslands of Australia.

6. Ways in Which Species Interact
There are five major types of species interactions.
Competition – each species negatively affects the other
Predation – one species consumes the other species
Parasitism – a smaller species feeds off of the tissues or fluids of another species
Mutualism – each species is helpful to the other
Commensalism – one species benefits from the relationship, but the other is unaffected

7. Ways in Which Species Interact
The categories of species interaction are based on whether harm or benefit is caused by the interaction.
Other types of interactions between species are possible.
Some types of interactions between individuals are atypical and do not represent the general trend as related to the species involved.
Many interactions in nature are still not well studied.

9. Competition
Competition is part of daily life for most species from male lions competing for who will dominate the pride to kudzu competing for sunlight as it overgrows a stand of trees in an interstate median.
Competition is a relationship in which individuals or populations attempt to use the same limited resource.
Each individual, as a result of the competition, has less access to the resource and is therefore harmed by the competition.

10. Competition
Competition can occur between individuals of a species or between species themselves.
Members of the same species tend to occupy the same niche, therefore, they will compete among themselves.
If the niches of two different species overlap, then they will compete for the resources.
Indirect competition is when species compete with one another for resources, yet they never come in direct contact while using the resources.
For example, humans compete with insects for the crops that we grow for food.

11. Competition
When two species with overlapping or similar niches are placed in the same ecosystem, the compete directly against one anther.
Sometimes one species out-competes the other and pushes it out of the habitat through competitive exclusion.
If the change is slow enough, one species may be able to adapt and change enough so that both species remain extant.
Niche restriction occurs when each species uses less of the niche than they are capable of using.
Niche restriction often occurs between two closely related species using the same resources in a habitat.

13. Predation
An organism that kills and consumes another organism is called a predator.
The organism that is fed upon is called the prey.
Predation is the relationship where a predator kills and consumes the prey.
A snake eating a mouse is an example of predation.
In complex food webs – typical of most ecosystems – predators can be the prey in some cases.

14. Predation
Most organisms have evolved some sort of defense against predation like the toxic taste of some toads or the shell of a tortoise.
Predator populations tend to mirror prey populations in an ecosystem with a short lag time.
For example, if a prey population spikes, the predator population will spike shortly thereafter due to the abundant food sorce.
When the predator population has increased, a decrease will be noticed in the prey population due to increased predation.

16. Parasitism
An organism that lives in or on another organism and feeds off of its tissues or fluids is called a parasite.
Parasitism is rarely fatal.
The parasite takes nourishment from the host organism.
Parasites are normally much smaller than their host.
Examples of parasites include ticks, fleas, hookworms, tapeworms, leeches, and mistletoe.

18. Mutualism
A close relationship between two species in which both species benefit is called mutualism.
Humans and intestinal bacteria are an example of mutualism because the bacteria help us with the breakdown of food and the synthesis of certain vitamins and our intestine provides habitat and food for these bacteria.
Termites and the intestinal protozoa are another example because termites alone cannot digest wood!

20. Commensalism
Commensalism occurs when a relationship exists in which one species benefits and the other species is neither harmed nor helped.
Remoras, which hitch a ride with a shark to get scraps of food, and sharks are an example of comensalism.
Birds used trees for habitat and neither harm, nor help the tree.

22. Symbiosis and Coevolution
Symbiosis is any relationship in which two organisms live in close association.
Many interactions are considered symbiotic in some way.
Over time, species involved in close relationships may coevolve.
Coevolution occurs when the evolutionary pathway of a species is affected by another species.

23. Symbiosis and Coevolution
Flowering plants and their insect pollinators often exhibit extreme cases of coevolution.
The development of articulation in brachiopods to starfish predation is another example of coevolution.

24. References
Arctic Food Web -
Bison -
Kangaroo -
Hippo and Tortoise -

25. References
Mammal That Ate a Dinosaur -
Barnacles and Niche -
Predator and Prey Populations -
Flea (parasite) -

26. References
Flea (musician) -
Mistletoe -
Tapeworm -
Trichonympha -

27. References
Termite Intestines Spilled -
Termites -
Remoras With Whale Shark -
Remora -

28. References Barnacles on a Whale - http://www.coreresearch.org/what.htm
Insect Pollination -