Visualizing Environmental Science

124 CHAPTER 5 How Ecosystems Work

5

Interactions Among Organisms 116

1. Symbiosis, an intimate relationship or association between
   members of two or more species, is the result of coevolution, the
   interdependent evolution of two interacting species. Mutualism
   is a symbiotic relationship in which both species benefit.
   Commensalism is a symbiotic relationship in which one species
   benefits and the other species is neither harmed nor helped.
   Parasitism is a symbiotic relationship in which one species (the
   parasite) benefits at the expense of the other (the host).


2. Predation is the consumption of one species (the prey) by
   another (the predator). With coevolution between predator

and prey, the predator evolves more efficient ways to catch

prey (such as pursuit and ambush), and the prey evolves

better ways to escape the predator (such as flight, association

in groups, and camouflage).

3. Competition is the interaction among organisms that vie
   for the same resources in an ecosystem (such as food or
   living space). Competition occurs among individuals within a
   population (intraspecific competition) and between species
   (interspecific competition).


4. A keystone species is crucial in determining the nature and
   structure of the entire ecosystem in which it lives. Though
   present in relatively small numbers, keystone species have
   disproportionate effects on ecosystems.

Key Terms

biosphere 99
community 98
competition 120
ecological niche 113
ecology 98

ecosystem 98

energy flow 103

first law of thermodynamics 100

landscape 98

photosynthesis 100

population 98

predation 119

second law of thermodynamics 101

symbiosis 116

What is happening in

this picture?

This dwarf frog in Brazil has an intriguing color pattern.

Note the two large spots on the frog’s rump. What
do they resemble? Why would this animal have such
conspicuous spots?

If a hungry bird saw this frog, do you think it would
have second thoughts about eating it? Why or why not?

What other strategies might this frog species use to
catch food or to avoid becoming food?

Critical and Creative Thinking Questions

1. To function, ecosystems require inputs of energy. Where
   does this energy come from?


2. After an organism uses energy, what happens to the
   energy? Is all the energy captured through gross primary
   productivity available to organisms higher in a food chain?
   Explain.
   3. What is a biogeochemical cycle? Why is the cycling of matter
   essential to the continuance of life? Why, specifically, is the
   cycling of nitrogen important to humans?
   4. What types of resources might two organisms compete
   over if those resources are scarce? How might interspecific
   competition affect two species’ ecological niches?

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