What is Ecology?
• Ecology studies how
populations of organisms grow & interact with each other to form
communities
- Communities are united
to form ecosystems, which includes relationships between living (biotic)
& nonliving (abiotic) components
- Ecology is:
- – The study of
biosphere
- – A branch of
biology
- – Not a social
cause or movement
- – Is not the same
as “environment”
- Today, 3 main branches
of ecology:
- – Population
ecology
- – Systems ecology
- – Applied ecology
Population Ecology
- • Population size is
determined by 4 factors
- – Natality (birth
rate)
- – Mortality (death
rate)
- – Immigration
(bring new individuals)
- – Emigration
(remove individuals)
•
Determining rate of growth allows one to predict if population will grow or
decline over time
• Population rate of growth
- – Determined by its
birth & death rates
- r =(b - d), where
r = population’s growth rate, b = birth rate, & d = death rate
- Population
dynamics is affected by 2 types of movement of individuals:
- – Immigration
- – Emigration
- • Now equation for
population growth looks like this:
- r = (b - d) + (i -
e)
- – New terms are i
= immigration rate and e = emigration rate
Exponential & Logistic Growth
- – Biotic potential
- • Population’s
ability to reproduce (intrinsic factors)
- –
Environmental resistance
- • Consists of
factors that limit growth (extrinsic factors)
- Some populations
grow exponentially – especially in early stages
- • With
exponential growth
- – Population
increases over time
- – Uncontrolled
growth goes on until space or resources are exhausted
•
Growth of most populations follows S-shaped curve
- – In nature,
populations are seldom left to their own devices
- Populations exhibiting
logistic growth do not grow exponentially
- – They grow
logistically as factors limit their growth
- • Some factors
are density-dependent
- • Others are
density-independent
- • Density-dependent
factors
- – Factors whose
effects depend on whether numbers are low or high
- – Raccoon rabies
outbreaks in northeastern US
- •
Density-independent factors
- – Some
environmental factors limit population but are unrelated to density
- – Sensitivity to
cold in flowing plants growing in Florida would be density-independent
- • Three factors that
help to predict how population may change
- – Number of
individuals already present (changes)
- – Population’s
carrying capacity (relatively constant)
- – Growth rate
(relatively constant)
K-Selection & r-Selection
- • Species are
K-selected
- – When they have
adaptations that permit them to live in a state of equilibrium
- – Close to
carrying capacities for long periods
-
- • Species are
r-selected
- – When they have
adaptations that permit them to rapidly increase their numbers
- – When their
populations are below their carrying capacities
K & r–Selected Species Comparison of
Characteristics
K-Selected Species
- • Live in stable
environment
- • Ecological
specialists
- • Have populations
stable in size
- • Compete well
against other species
- • Are restricted in where
they can live
- • Are long-lived
- • Have few,
relatively large young
- • Have long periods
of embryonic development
- • Reach adulthood
slowly
- • Invest intensive
care in young
- • Reproduce
throughout lifetime
Interactions of Populations
- • Interactions between
populations are complex & difficult to study
- • Intensity of
interactions may be slight or great
Interactions of Populations
• When populations compete, both are harmed
– Two types of competition:
• Competition between individuals within their own species for food, space,
mates
• Competition between species for food, space, but never for mates
• What are the results of competition?
– It is density-dependent
– In ideal environment competition is not a factor
– As populations grow, interactions between competitors intensify
•
One species will exclude the other
• They will partition resources so that competition is minimized &
tolerable
Predator & Prey
Interactions
- • Populations
regularly exploit other populations as sources of nutrients & energy
- • One population
(predator) benefits at expense of other (prey)
- • Predation is
density-dependent factor
- • Predator/prey
relationships can be used to control unwanted populations
-
- Plants &
Herbivores
- • Plant/herbivore interaction
- – Herbivores find
plants & eat them
- • Most herbivores
prefer specific type of plant species & seek them out
- • Herbivores
responded evolutionarily
- – plant cells have
cellulose that is difficult to digest
- • Herbivores
digestive systems are more complex than those of carnivores
- • Plants may respond
to herbivores
- – In passive
fashion – make enough tissue to feed herbivores & still live
- • Plants may also
respond in less passive way
- – By releasing
hormones that deter further feeding
- • Some are
distasteful & avoided by herbivores
-
- Herbivores &
Carnivores
- •
Herbivore/carnivore interactions
- – Carnivores must
find, approach, & secure prey
- – Herbivores must
sense presence of predators & avoid them
- • Carnivores get
more energy from animal material
- – It is easier to
digest & nutrients are highly concentrated
- • It is to
carnivore’s advantage to secure most food while expending least energy
- • Energy expenditure
is important to prey species too
- • Carnivore
initiates chase & prey responds
- • Being
inconspicuous is important to both prey & predators
Symbioses
- • Some populations
form intimate associations
- – Interactions
between a pair of species can become so intimate that one or both become
dependent on the other
- Symbioses • There
are 3 basis types of symbioses:
- – Parasitism
- – Commensalism
- – Mutualism
-
- • Parasitism -
interaction between parasite & host
- – Parasites have
at least one host, some may have multiple hosts
- • Commensalism
- – One species
benefits while other is seemingly unaffected
- • Mutualism
- – Both species
benefit
- – Partnerships in
life are formed
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