Ecologists sampling a meadow lay a square frame called a quadrat at random spots and count the plants inside it.
Missing Word
quadrat
A quadrat is a square sampling frame placed at random locations so that counts inside it can be scaled up to estimate the whole population. It works best for plants and other organisms that stay in place.
Category: Population Measurement
Question 2
Demography is the statistical study of populations, including their birth rates, death rates and age structure.
Missing Word
Demography
Demography examines how populations change over time by measuring births, deaths and age distribution. Tools such as life tables and survivorship curves are central to it.
Category: Demography
Question 3
Malaria is caused by Plasmodium, a single-celled protist that lives as a parasite in human blood and is spread by mosquitoes.
Missing Word
Plasmodium
Plasmodium is a protist parasite that is carried by mosquitoes and infects human red blood cells, causing malaria. It is a standard example of parasitism, in which one organism benefits at the expense of a host that it harms.
Category: Species Interactions
Question 4
The logistic model of population growth adds a carrying capacity term, so growth slows and levels off as resources become limited.
Missing Word
logistic
The logistic model multiplies exponential growth by (K - N)/K, which shrinks toward zero as the population nears carrying capacity. Graphed over time it forms an S-shaped curve, as yeast grown in a test tube does.
Category: Growth Models
Question 5
Dandelions, which make huge numbers of small, wind-dispersed seeds that receive no parental care, are classic r-selected species.
Missing Word
r-selected
r-selected species are adapted to unstable, unpredictable environments, where producing many offspring quickly pays off. They sit at the opposite end of the life history continuum from K-selected species such as elephants.
Category: Population Regulation
Question 6
Emigration, the movement of individuals out of a population to live elsewhere, reduces the size of the population they leave.
Missing Word
Emigration
Emigration is the departure of individuals from a population. Population size rises with births and immigration and falls with deaths and emigration.
Category: Population Regulation
Question 7
Competition between members of two different species for the same limited resource is called interspecific competition.
Missing Word
interspecific
Interspecific competition occurs between species, while intraspecific competition occurs within one species. When two species compete for exactly the same resources, one may eliminate the other.
Category: Species Interactions
Question 8
A species' niche is the unique set of resources it uses and the role it plays in its environment.
Missing Word
niche
A niche includes the food, space and conditions a species needs and how it interacts with others. Two species cannot share an identical niche indefinitely, because the better competitor will exclude the other.
Category: Species Interactions
Question 9
Symbiosis is a close, long-term association between individuals of two different species.
Missing Word
Symbiosis
Symbiosis covers relationships in which two species live in close contact over a long period. It includes mutualism, commensalism and parasitism, which differ in who benefits and who is harmed.
Category: Species Interactions
Question 10
A tapeworm living in a human intestine and absorbing nutrients at the host's expense is an example of parasitism.
Missing Word
parasitism
Parasitism is a relationship in which one organism benefits by living on or in a host that it harms, usually without killing it quickly. Tapeworms are often picked up from undercooked meat.
Category: Species Interactions
Question 11
The sea star Pisaster is a keystone species, because removing it lets mussels crowd out many other species in tide pools.
Missing Word
keystone
A keystone species has an effect on community structure far larger than its abundance would suggest. Pisaster preys on mussels, keeping them from monopolizing space and preserving the diversity of the tide pool.
Category: Community Structure
Question 12
Succession is the gradual, sequential replacement of one group of species by another in a community over time.
Missing Word
Succession
Succession describes how a community changes after new land forms or a disturbance occurs. It is called primary when it starts without soil and secondary when soil remains.
Category: Community Structure
Question 13
Hardy organisms that are the first to colonize bare rock or newly cleared ground are called pioneer species.
Missing Word
pioneer
Pioneer species tolerate harsh conditions and begin changing the site, for example by building soil, which allows later species to move in. In secondary succession, annual plants and grasses often fill this role.
Category: Community Structure
Question 14
On fresh lava rock, some of the earliest colonizers are lichens, partnerships of a fungus with algae or cyanobacteria that slowly break rock down into soil.
Missing Word
lichens
Lichens are mutualistic partnerships between a fungus and a photosynthetic partner. They can survive on bare rock and release substances that help weather it, starting the soil that plants later need.
Category: Community Structure
Question 15
The relatively stable community that develops at the end of a long series of changes, and lasts until the next disturbance, is called a climax community.
Missing Word
climax
A climax community is the mature, fairly stable endpoint of community change for a given climate and geology. An oak and hickory forest is an example in parts of eastern North America.
Category: Community Structure