Ecology

1
Ecology

• An Introduction and Population Growth

2
Ecology

• Ecology is the science that deals with the
  interrelationships among living things and their
  environment.
• The science deals with words like ecosystem,
  community and population

3
Ecology

• Lets recall the definitions of these words.
• Ecosystem a complex, interrelated network of
  living organisms and their nonliving
  surroundings.
• Community interacting populations.
• Population consists of all the members of a
  particular species.
• Individual is the single organism.

4
Ecology

• When studying ecology we are studying the
  environment, but it is important to specify what
  parts of the environment.
• Abiotic non-living component
• Biotic living component

5
Populations

• Studies have shown that many populations remain
  stable over time but there are examples of growth
  and decline.
• The factors that control this are
• Births, deaths, and migration

6
Populations

• Organisms can join a population through
• Immigration (migration in)
• Birth
• Oganisms can leave a population through
• Emigration (migration out)
• Death

7
Populations

• Thus simply a populations change can be difined
  as
• Population Change (births-deaths)
  (immigrants-emigrants)
• Because generally migration plays a minor roll in
  population size whe can discuss the factors
  determining ultimate size of the population
  without them

8
Populations

• This final size is the result of a balance
  between two major opposing factors
• Biotic Potential or the maximum rate at which
  the population could increase, assuming ideal
  conditions allowing a maximum birth rate and
  minimum death rate.
• Environmental Resistence all living and non
  living environmental factors working against
  providing these ideal conditions

9
Populations

• Population size is a function of birth rate,
  death rate, and the number of individuals in the
  original poplulation.
• Growth Rate Birth Rate Death Rate
• Births per 1000
• Deaths per 1000
• Growth Rate
• Eg.

10
Populations

• Population growth can then be defined as
• r or growth rate N or number of original ind.
• If growth rate is constant this equation become
  exponential.

11
Populations

• Exponential Growth the populations grows
  (during a given time period) by a fixed
  percentage of its size at the beginning of that
  time period.
• Eg. Arithmatic v. Exponential
• J - curve

12
Human Population Growth
13
Populations

• Some of the factors affecting the biotic
  potential of a particular species are (,-) Eg.
• The age at which the average individual first
  reproduces
• The average frequency with which reproduction
  occurs
• The average number of offspring produced each
  time
• The reproductive life span of the average
  organism
• The average death rate under ideal conditions

14
Populations

• Exponential growth can often lead to boom and
  bust cycles.
• What could cause these boom and bust cycles?
• Exotic Species?

15
Populations

• Exponential growth carries with it the seeds of
  its own destruction.
• Increase competition
• Predators
• Parasites and disease
• Stress
• S-curves around equilibriums

16
Populations

• Populations ussually stabalize at or below their
  carrying capacity.
• Carrying capacity is the maximum size of a
  given population of organisms that a particular
  area can support indefinitely.

17
Populations

• The carrying capacity is controlled mainly by two
  types of resources
• Renewable resources, such as nutrients, water,
  and light, that are replenished by natural
  processes
• Nonrenewable resources such as suitable nesting
  or denning areas

18
Populations

• Organisms will die if demads on renewable
  resources such as food, water,a dn light are too
  high

19
Populations

• In nature, environmental resistance maintains
  populations at or below the carrying capacity of
  the environment. This is done through two
  factors
• Density-independent factors limiting population
  size regardless of the density
• Density-dependent factors increasingly
  effective as the population density increases

20
Populations

• Density Independent Factors
• Natural Events (hurricanes, droughts, floods and
  fire)
• Weather (seasonal reproduction limit)
• Not reaching carrying capacity
• Boom and bust cycles
• Human Activities
• Pesticides and pollutants
• Habitat destruction

21
Populations

• Density Dependent Factors which affect long lived
  species the most
• Predation
• Competition with in the species or with members
  of other species
• Parasitism

22
Density Dependent Factors

• Predators and Parasites
• Both of these processes involve one organism
  feeding on another and harming it in the process
  (not necessarily in the case of parasitism)
• Predator Prey
• Parasite Host

23
Density Dependent Factors

• Increase Prey?
• Increase Predator?
• Population Cycles?

24
Density Dependent Factors

• Parasites slow work?
• Limitted mobility?
• Population density?
• Effect predation also?

25
Competition for Resources

• Competition the interaction among individuals
  who attempt to utilize a limited resource, limits
  population size in a density-dependent manner

26
Competition for Resources

• Interspecific competition?
• Intraspecific competition?
• Scramble competition? (seed dispersal)
• Contest competition? (social and chemical
  interations, territory)

27
Distribution of Populations

• Clumped
• Uniform
• Random