Populations & Communities Study Guide
Vocabulary Words
Competition: the struggle between organisms to survive as they attempt to use the same limited
resource
Population: all the members of one species in a particular area
Abiotic factors: the nonliving parts of an ecosystem
Mutualism: a symbiotic relationship in which both species benefit
Carrying capacity: the largest population that an environment can support
Ecosystem: the community of organisms that live in an area, along with their nonliving surroundings
Species: a group of organisms that are physically similar and can reproduce with each other to produce
fertile offspring
Limiting factors: environmental conditions that prevent populations from increasing
Commensalism: a symbiotic relationship in which one species benefits and the other species is neither
helped nor harmed
Community: all the different populations that live together in an area
Biotic factors: the living parts of an ecosystem
Adaptations: behaviors and physical characteristics of species that allow them to live successfully in
their environment
Predation: an interaction in which one organism kills and eats another organism
True/False
T; If a population is very large or spread out, ecologists use the sampling method to estimate the
population size.
F; Community; All the different species living in an area form a population.
T; An organism’s specific role in its habitat is called its niche.
F; adoptions; Every organism has a variety of habitats that enable it to live successfully in its
environment.
T; Water, sunlight, and oxygen are examples of abiotic factors in ecosystems.
Problems
Students counted 45 sand crabs in a 5-meter by 3-meter section of a beach. What was the population
density of sand crabs in that section? 3 crabs per square meter (5 m x 3 m = 15 m squared; 45 crabs / 15
m squared = 3 crabs per m squared)
The entire beach measured 40 meters by 15 meters. Estimate the total population of sand crabs on
the entire beach. 1,800 crabs (40 m x 15 m = 600 m squared; 600 m squared x 3 crabs per m squared =
1,800 crabs
Essay
Use an example to explain how a limiting factor can prevent a population from increasing indefinitely.
Limiting factors include the amount of food available, the amount of space available, and weather
conditions. At some point, limiting factors would cause the population to begin decreasing.
Identify one example of parasitism, and describe the interaction between the two species. Explain
why parasites usually do not kill their hosts.
One example of parasitism is a tapeworm (the parasite) living inside a dog (the host). The tapeworm
benefits because it gets food from the dog. The dog is harmed because the tapeworm takes nutrition
from the dog and weakens it. Parasites usually do not kill their hosts because they would then lost their
sources of food.
Graphs/Charts
There will be a picture of a nature scene and you will have to identify all the biotic factors and abiotic
factors. Also, you will have to identify the specific habitat of each animal that is listed.
There will also be pictures showing the process of succession and how it can change over time. You will
have to tell me what type of succession is being shown in the pictures (primary/secondary). Describe
animals that can and cannot survive in a forest ecosystem based on the pictures, and describe to me
how the ecosystem changed from picture to picture.