population size

populations

Biotic and abiotic factors determine the population size of a species in an ecosystem. What are some important biotic factors? Biotic factors include the amount of food that is available to that species and the number of organisms that also use that food source. What are some important abiotic factors? Space, water, and climate all help determine a species population. When does a population grow? A population grows when the number of births is greater than the number of deaths. When does a population shrink? When deaths exceed births. What causes a population to grow? For a population to grow there must be ample resources and no major problems. What causes a population to shrink? A population can shrink either because of biotic or abiotic limits. An increase in predators, the emergence of a new disease, or the loss of habitat are just three possible problems that will decrease a population. A population may also shrink if it grows too large for the resources required to support it.

carrying capacity

When the number of births equals the number of deaths, the population is at its carrying capacity for that habitat. In a population at its carrying capacity, there are as many organisms of that species as the habitat can support. The carrying capacity depends on biotic and abiotic factors. If these factors improve, the carrying capacity increases. If the factors become less plentiful, the carrying capacity drops. If resources are being used faster than they are being replenished, then the species has exceeded its carrying capacity. If this occurs, the population will then decrease in size.

limiting factors

Every stable population has one or more factors that limit its growth. A limiting factor determines the carrying capacity for a species. A limiting factor can be any biotic or abiotic factor: nutrient, space, and water availability are examples (Figure 1.1). The size of a population is tied to its limiting factor. What happens if a limiting factor increases a lot? Is it still a limiting factor? If a limiting factor increases a lot, another factor will most likely become the new limiting factor. This may be a bit confusing, so lets look at an example of limiting factors. Say you want to make as many chocolate chip cookies as you can with the ingredients you have on hand. It turns out that you have plenty of flour and other ingredients, but only two eggs. You can make only one batch of cookies, because eggs are the limiting factor. But then your neighbor comes over with a dozen eggs. Now you have enough eggs for seven batches of cookies, but only two pounds of butter. You can make four batches of cookies, with butter as the limiting factor. If you get more butter, some other ingredient will be limiting. Species ordinarily produce more offspring than their habitat can support (Figure 1.2). If conditions improve, more young survive and the population grows. If conditions worsen, or if too many young are born, there is competition between individuals. As in any competition, there are some winners and some losers. Those individuals that survive to fill the available spots in the niche are those that are the most fit for their habitat. Click image to the left or use the URL below. URL: A frog in frog spawn. An animal produces many more offspring than will survive.

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instructional diagrams

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questions

when does a population shrink?

a) the number of births equals the number of deaths.

b) the number of births is greater than the number of deaths.

-->  c) the number of births is less than the number of deaths.

d) randomly.

a region will be at its carrying capacity if

-->  a) the number of births equals the number of deaths.

b) the number of births is greater than the number of deaths.

c) the number of deaths is greater than the number of births.

d) the resources are being used faster than they are being replenished.

the size of a population in an ecosystem is determined by

a) biotic factors such as the food available and the competition for that food.

b) abiotic factors such as space, water and climate.

c) the carrying capacity of the ecosystem for that species.

-->  d) all of the above.

if a pack of coyotes enters a region, the carrying capacity for bunnies will likely

-->  a) decrease.

b) increase.

c) not be impacted.

d) respond randomly.

besides changes in births and deaths, immigration in or out of a region can also change a population.

-->  a) true

b) false

for a given species in a given habitat, the limiting factor is always the same thing.

a) true

-->  b) false

why do some animals produce many more offspring than their habitat can support?

a) if conditions improve and more can be supported in the habitat, they will be ready.

b) if conditions worsen, competition will ensure that the fittest survive.

c) to be sure that some will survive.

-->  d) all of the above.

what is an important abiotic factor to help a population grow?

a) predators

-->  b) space

c) food supply

d) all of the above

if a population uses needed resources faster than they are being replenished, the population

a) has yet to reach its carrying capacity.

b) will continue to grow forever.

-->  c) has exceeded its carrying capacity.

d) none of these.

a limiting factor determines the carrying capacity for a species.

-->  a) true

b) false

diagram questions

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