Studied by 1 personcarrying capacity
the carrying capacity is the maximum number of organisms that can be sustained in a population.
if the population number increases above the carrying capacity, there will not be enough resources like food, water and space.
the number of individuals will decline
limiting factor
the factor whose magnitude slows down the rate of a natural process
population size and carrying capacity
population size of a species can:
-remain stable
-rise or fall quite suddenly
-oscillate with a regular pattern
the balance between death rate (mortality) and the rate of reproduction determines the size of a population
K-strategists
A= lag phase → there may only be a few individuals, they are still acclimatising to their habitat. at this point, the rate of reproduction is low, and the growth in population size is slow
B=log phase → resources are plentiful and conditions are good. reproduction happens quickly exceeding mortality
C=stationary phase → the population has levelled out at the carrying capacity of the habitat. the habitat cannot support a larger population. in this phase, the rates of reproduction and mortality are equal. the population remains stable or shows very small fluctuations
limiting factors
-the reason a habitat has a carrying capacity is because a factor is limiting further growth
-some factors act just as strongly regardless of population size. (density independent) e.g. low temperatures will kill the same proportion of the population irrespective of its size
-others are dependent on size (density dependent) and the factor’ influence increases with size
K strategist
-this is when the population is determined by carrying capacity
-for these populations the limiting factors exert a more and more significant effect as the population size gets closer to the carrying capacity leading to a levelling out
-birds, larger mammals and larger plants are K-strategists
K strategists- characteristics
-low reproductive rate
-slow development
-late reproductive age
-long lifespan
-large body mass
R-strategists
-some species adopt a different type of population growth
-the population size often increases so quickly that it exceeds the carrying capacity before the limiting factors take effect
-then there are no longer enough resources to allow reproduction or survival
-the quick build up of waste can also poison the species
-this model is often called boom and bust
R strategists- characteristics
-mice, insects, weeds and spiders
-high reproductive rate
-quick development
-young reproductive age
-short life span
-small body mass
boom- conditions are good and then get over the carrying capacity
bust- resources run out and they die off
interspecific competition
competition between individuals of different species
intraspecific competition
competition between individuals of the same species
predators and prey 1
a predator is an organism that feeds on another lviving organism (prey) for its food
prey is def on by predators
with time predators evolve to become better adapted for capturing their prey; faster movement, more effective camouflage, better means of detecting/tracing prey
prey have also become better adapted otherwise the entire species of predators that feed on them would die
predators and prey 2
both the predator and the prey evolve together if this had not happened they would have become extinct
when a population of predators and prey are brought together in a lab the prey is usually exterminated
this is due to the unnatural limited range of habitats available. outside of a lab the prey numbers can often drastically drop without becoming extinct. therefore, this must be studied in the wild whenever possible
predator and prey- the relationship
predators eat their prey reducing numbers
with fewer prey available the predators are in greater competition with each other
the predator population is reduced as some individuals are unable to obtain enough prey
with fewer predators left, fewer prey are eaten
the prey population increases
predator numbers increase
competition
this happens when resources are in limited supply
organisms have to complete for this resource
as competition intensifies the reproduction rate decreases and death rate increases
intraspecific competition
within the species the best suited individuals survive and reproduce, while those not so suited fail to reproduce and/or die
this causes the population to enter a stationary phase
if the population size drops, competition will reduce and the population size can increase again
if the population size increases, more competition occurs leading to a drop
interspecific competition
in this case the competition can alter the distribution of species in an ecosystem
interspecific competition- case study I
two species of Paramecium were grown separately and together in a lab
when together they competed for food. P.aurelia obtained food more effectively than P.caudatum
over 20 days the P. caudatum died out
interspecific competition- case study II
the scientist concluded that the more overlap between two species’ niches the more intense the competition
if 2 species have the same niche, one will be totally out-competed by the other
two species cannot occupy the same niche
this idea is known as the competitive exclusion principle
interspecific competition- case study III
it is often not quite so extreme with one species simply being much smaller than the other with both populations remaining constant in size
in a lab other variables are often excluded
as the environment is constantly changing it is rare for one species to be totally wiped out
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