1. Species relationships
• relate the presence of particular animals in the local environment to their requirements within the local environment

2. 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 ecosystem.

3. Population at equilibrium

4. 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.

5. Predator prey cycles

6. 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.

7. 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.

8. 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.

9. Parasitism An example is mistletoe.
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.

10. 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.

11. Allelopathy in action