Populations and Community Interactions

Chapters 39 and 40

I.          Population Growth and Regulation

            A.        General Definitions

1.         Ecology – the study of interactions between living things and their nonliving environment

2.         Abiotic – nonliving (i.e. rocks, air, weather)

3.         Biotic – living

4.         Ecosystem – all abiotic and biotic components within a defined area.

5.         Community – all interacting populations of organisms in an ecosystem.

            B.         How does population size change?

1.         Population – all members of a particular species in a given ecosystem that have the potential to interbreed.

2.         Changes in population are dependent on the following –

            a.         The number of birth compared to deaths

b.         The number of individuals that immigrate into a population compared to the number of individuals that emigrate out of the population.

c.         The mathematical relationship between these characters

Change in Population Size = (birth – death) + (immigration – emigration)

d.         Biotic potential – the maximum rate at which a population can increase given maximum birth rate and minimized rate of death.

e.         Environmental Resistance – the limits set on population expansion by the ecosystem.

                        3.         The idea of biotic potential can lead to exponential growth

a.         Exponential Growth is the continuously accelerating increase in population growth.

b.         If you graph the growth of a population in exponential growth you will get the classic ‘J-curve’ (see class)

c.         We can also calculate the doubling time for a population, the amount of time needed to double the size of the population.

            C.        How is population growth regulated?

                        1.         Populations can not grow exponentially forever.

a.         Every environment has limited resources available to a population.

b.         Most population will progress through a boom-and-bust cycle dealing with routine massive die-offs and population recoveries

            i.          Think about how this may affect the allele          frequencies in a population

ii.          Artificial influences can alter the normal flow of the boom/bust cycle (see exotic species)

c.         Environmental Resistance applies limits on the growth of a population.

            i.          S – curve

ii.          Carrying Capacity – the maximum population size that an ecosystem can sustain.

d.         Density – Independent Factors can affect population growth no matter the population size.

e.         Density – Dependent Factors becomes more effective as population density increases.

            i.          Predator and Parasites can control populations

ii.          Competition for resources is a strong control for the population as density increases.

iii.         Surviorship Curves

II.        Community Interactions

            A.        Community Interactions

1.         Community – all interactions between the biotic members in a ecosystem.

2.         Coevolution – the interaction of species that act as natural selection agents upon each other.

3.         Types of Interaction –

            a.         Competition

            b.         Predation

            c.         Symbiosis – “living together”

                        i.          Parasitism

                        ii.          Commensalism

                        iii.         Mutalism

            B.         What are the effects of competition among species?

1.         Interspecies Competition – multiple species competing for the same resources.

2.         Competitive Exclusion Principle – multiple organisms can not thrive in the same environmental niche, they will compete until only one survives.

C.        Succession – a structural change in a community and its living and nonliving interactions.

            1.         Succession is preceded by a disturbance to the original community.

a.         Pioneers – hardy plant invaders that are the first ones to enter a new environment.

b.         Climax community – a diverse, rather stable community

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