6.6 Flashcards
what determines the size of a population
the balance between death (mortality) rate and the rate of reproduction
population growth is shown on page 290, explain point a (the lag phase)
there may only be a few individuals which are acclimatising to their habitat. At this point, the rate of reproduction is low, and the growth in population size is slow
population growth is shown on page 290, explain point b (the log phase)
resources are plentiful, and conditions are good. Reproduction can happen quickly, with the rate of reproduction exceeding mortality. The population size increases rapidly.
population growth is shown on page 290, explain point c (the stationary phase)
the population size has levelled out at carrying capacity of the habitat- the habitat can no longer support a larger population. In this phase, the rates of reproduction and mortality are equal. The population size therefore stays stable, or fluctuates very slightly up and down in response to small variations in environmental conditions each year.
define carrying capacity
the maximum population size that can be maintained over a period in a particular habitat.
why can a habitat that has reached carrying capacity not support a larger population
because limiting factors limit growth in population
some limiting factors are density independent, what does this mean
these limiting factors act just as strongly, irrespective of the size of the population. For example, particularly low temperatures may kill the same proportion of individuals in a population, irrespective of its size
some limiting factors are density dependent, what does this mean
this is where the factor influences population more strongly as population size increases.
E.g, the availability of resources like food, water, light, oxygen, nesting sites or shelter may decrease. Similarly, as population size increases, levels of parasitism and predation from other species may increase, as do the intensity for of competition for resources, both within individuals of the same species and the individuals of other species. The carrying capacity is the upper limit that these factors place on population size.
what is the most important influence on population growth
and what is its characteristic of
the most important influence on population growth is the physical rate at which an organism can reproduce.
This type of growth is characteristic of species with short generation times (such as bacteria) and pioneer species
how are habitats affcted by the speed of quick population growth
quick population growth means pioneer r-strategists species colonise a disturbed habitat before k-strategists , dispersing to other habitats once limiting factors start to ahve an affect
define limiting factor
the factor whose magnitude slows down the rate of a natural process
what is a limiting factor on a preys population size
predators/ predation
predation can act as a limiting factor on a preys population size, which in turn can affect the predators population, explain this (5)
- When the predator population gets bigger, more prey are eaten.
- The prey population then gets smaller, leaving less food for the predators
3.With less food, fewer predators can survive and their population size reduces.
- With fewer predators, fewer prey are eaten, and their population size increases
- With more prey, the predator population gets bigger, and the cycle starts again
figure 1 shows a predator prey cycle made in a laboratory, figure 2 (more jutted) comes from studies on wild populations, explain why the relationship in figure 2 is not as clear as in figure 1.
in the lab, the predators only ate one type of prey, and predation was the main limiting factor on the preys population. However, in the wild, predators often eat more than one kind of prey, and there are numbers of other limiting factors. This is why there isn’t a defined shape in the wild
what is competition
occurs when resources are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources.
what rate decreases as competition increases/ intensifies
as competition increases, the rate of reproduction decreases (not enough resources to reproduce)
what rate increases as competition increases/intensifies
as competition increases, the death rate increases because fewer organisms have enough resources to survive
what are the two types of competition
intraspecific and interspecific
define intraspecific competition
competition between individuals of the same species
when factors become limiting, what stage will population levels reach through intraspecific population
population levels will slow down and reach a stationary phase. (best adapted will be alive)
intraspecific population keeps the population size relatively stable.
if population drops will competition increase or decrease
competition will decrease and this will allow populations to grow again
define interspecific competition
competition between individuals of different species.
This can affect population size of a species, and distribution of a species in an ecosysem
describe Gauses experiment on testing interspecific competition.
He grew two species of Paramecium, both separately and together.
When together, there was competition for food, with P.aurelia obtaining food more efficiently than P.caudatum. Over 20 days, the population of P.caudatum reduced and died out, whereas only the population of P.aurelia increased being the only species remaining.
describe the graph for P.aurelia and P.caudatum in competition
-P.aurelia population growth is slower than when it grows alone, and only when the P.caudatum dies out does the population reach the size of it grown alone
-P.caudatum population initially grows faster in the presence of P.aurelia than alone, but soon declines cus P.aurelia outcompetes it for food
what was Gauses conclusions after the experiment
Gause concluded that more overlap between the two species niches results in more intense competition. If two species have the exact same niche, one is outcompeted by another and dies out or comes extinct in that habitat; two species can not occupy the same niche. This idea is called the competitive exclusion principle, and can be used to explain why particular species only grow in certain places.
why are Gauses conclusion not fully correct
-other conclusions suggest that extinction is not necessarily inevitable.
-sometimes, interspecific competition results in one population being much smaller than another, with both population sizes remaining relatively constant
explain why the competition exclusion principle does not always apply in natural ecosystems
-in a lab, effects of other variables can be excluded so the habitat of two species remains stable.
-In the wild, a wide rand of variables may act as limiting factors for the growth of different populations, and may change on a daily basis.
give an example of where the competition exclusion principle does not always apply in natural ecosystems
experiments of competition between flour beetles T. confusumand T.castaneum initially confirmed the competitive exclusion principle. - The T.castaneum population size increases while the T. confusum population died out.- but even a small change in temperature (a factor) could change the outcome so would survive instead.
