U N I T 3 : E C O L O G Y
Population Constraints z
Carrying capacity is the largest population of organisms that an area and its resources can support. For example, if
the plants in an area are able to provide 10 kilograms of foliage or leaves each week to be consumed by first-order
consumers, and a single rabbit needs 1 kilogram of foliage per week to survive, then this area can support 10 rabbits.
This is its carrying capacity. If any environmental factors decrease the carrying capacity of an area, the population
size will decrease, also.
HOW DEEP IS THE BARREL?
Consider this illustration of muskrats that die each year due
representing muskrats in to starvation, predators, disease, or
a marsh. The barrel other factors. The barrel can only
represents the marsh hold so much water. That is, there
habitat - the is a limit to
amount of the
food, water, number of
and cover muskrats
for a ﬁxed that can
number of muskrats. survive
Graphing Capacity The water in the barrel here from
As new animals are added, is the number of year to
the population grows, but muskrats the habitat can year unless
limiting factors prevent the support. The pipe the habitat
entire population from pouring water into the (the size of
surviving. This leads to a drop
barrel represents the the barrel)
in the population. The
carrying capacity is the new muskrats that are is changed
number of organism’s a given born in the marsh or in some
area can support over time. wander in from other way.
places. The water
spilling out is the number
Limiting Factors Common limiting factors include:
Because of the limited
supply of basic re-
Environmental factors that limit Water sources, some organ-
or decrease the carrying capacity Amount of Space isms will COOPERATE to
of an area are known as Climate and Weather including meet basic needs, while
LIMITING FACTORS. Catastrophic Events others will COMPETE
with one another.
A B D
.The pictures above show the effects of limiting factors on various populations. In A, a pelican competes
with a duck for the same food source. Figure B shows the mutualistic symbiotic relationship between
bees and a daisy - the bee gets nectar and the daisy gets pollination. Figures C and D show competition
between members of the same species - the insects in ﬁgure C are competing for food and the rams in
ﬁgure D are competing for mates.
1. What is carrying capacity?
2. What is a limiting factor? Give two examples.
3.Each owl needs to eat 3 small rodents per day to survive. You take a population sample and discover
2,190 rodents living in a large pasture. How many owls could this support in one year? (Remember
there are 365 days in a year.) Show your work.
4. Remember the energy pyramid, and think about carrying
capacity. At which trophic level would you expect to see more
competition, primary level consumers or tertiary level