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Species relationships
• relate the presence of particular
animals in the local environment to
their requirements within the local
environment
Population trends
A population is the number of a particular
species living in a particular area.
When a species first moves into an area, e.g.
a feral animal or after a big disturbance, its
population will usually increase rapidly.
However, a time will come when the
organism will have outgrown the carrying
capacity of the ecosystem to support that
population.
There will then be a crash in the population
followed by a slower rise.
Most organisms will then come into some sort
of equilibrium where they fluctuate slightly
around the carrying capacity of the
Population at equilibrium
Predator and prey
A predator is a species that feeds on other
species - prey species.
The populations of predators and prey are
intricately connected.
Predator/prey cycles:
as prey populations increase, so do the numbers
of predators
as predators increase the growth of the prey
population will slow and eventually decrease
as the prey population decreases there will be a
drop in the number of predator species
when the predator numbers drop below a certain
point the prey species will increase
Predator-prey cycles can cause large spikes
and drops in population numbers.
Predator prey cycles
Relationship types
Different species interact with each other in
different ways.
These interactions may be beneficial for both
species (mutualism), benefit one species
while not effecting the other organism
(commensalism), or benefit one species to
the detriment of other species (allelopathy,
parasitism).
These relationships can help determine how
successful a species is in its ecosystem.
Mutualism, commensalism and parasitism are
different types of symbiosis (‘living together’)
where at least one species benefits from the
relationship.
Mutualism
Mutualism is a relationship where both
species involved receive some benefit from
the relationship.
An example is lichens.
lichens are a symbiotic relationship between an
algae and a fungus.
algae contain chlorophyll and can
photosynthesise, but require a moist environment.
the fungi provides the habitat requirements for the
algae, and in return the algae supplies the fungus
with food.
Other examples include mistletoe and
mistletoe birds, cows and cattle egrets,
sharks and remora, figs and wasps.
Commensalism
Commensalism benefits one organism without
having any effect on the other organism in the
relationship.
An example is between clown fish and sea
anemones.
anemones have stinging tentacles that protect them
from being eaten by small fish.
clown fish excrete a mucous onto their skin that
protects them from the sea anemones tentacles
clown fish will take up residency within the tentacles
of the sea anemone - this protects them from
predators but gives no benefit to the anemone.
Another example of commensalism is between
trees and epiphytes.
Parasitism
A parasitic relationship is one in which one organism
(the parasite) derives benefit from another organism
(the host) to the host’s detriment.
An example is mistletoe.
mistletoes are a type of shrub that germinate in the
branches of other trees
instead of sending roots down into the soil, they send
their roots down into the sapwood of the host tree
mistletoes get most of their food from the nutrients in
the host trees sap
a large number of mistletoes on the one tree can
cause the host tree to become sick or even die.
Other examples of parasites include: ticks,
fleas, mosquitoes, tape worm, etc.
Allelopathy
Allelopathy is a feature of certain plants.
Plants that display this feature release
chemicals into the soil through their root
system.
These chemicals (allelochemicals) can inhibit
the germination or growth of other plants in
the root zone.
This confers a competitive advantage to the
species releasing the allelochemicals.
Examples of plants that exhibit allelopathy
include some She-Oaks (Casuarina spp.),
Camphor Laurels, and some Eucalypts.
Allelopathy in action