What is ecology?
- the way in which organisms interact with their environment (including other organisms)
- also the name for the study of these interactions
- these processes drive evolution by natural selection
What is evolution?
- the change over time of inherited traits found in populations of individuals
- evolution is genetic change
- not design, or predetermine by the organism- eg. the snail did not decide to make a shell to avoid predation
- rather natural selection favours individuals that have traits that give them an advantage, meaning they are more likely to survive and reproduce
- these adaptations are inherited by their offspring
What are examples of how interactions with other animals can drive evolutionary change:
- males are often very colourful
- the most colourful males females and predators
- stream with high numbers of predators have dull males
- dull male population introduced into predator-less stream, become brightly coloured within two generations
- how ecology can drive evolutionary change
- when lot of predators= not as colourful (the advantage of attracting more females is outweight by the attraction of predators)
- no predators= lot mor ecolourful males over time
What are the 4 levels at which ecology can be studied?
- Ecosystem
- Community
- Population
- Individuals
What is an ecosystem?
An entire environment, its physical properties and all the organisms and communities found there.
What is a community?
- any group of species that live in the same place and potentially (or actually) interact with each other
- can refer to a collection of related species in an area (eg. Darwin’s finches in the Galapagos)
- communities can describe interactions between just a few (even two) species in the same area
- eg. Ragwort= aphids feed on ragwort, ants feed on the aphid honeydew
- cinnabar moth caterpillars feed on ragwort but damage it
- damaged= ragwort= bad for aphids= bad for ants
- ants attack cinnabar moth caterpillars and remove them from the ragwort
What is a population?
- a group of individuals of the same species
- population ecology involves understanding why species numbers vary and the causes of variation within species
What is symbiosis?
-when two species interact closely together in a way which is beneficial to one or both
-interaction can be either essential to existence of one or both species (OBLIGATE) or not (FACULTATIVE)
-three types of symbiosis
=Mutualism
=Commensalism
=Parasitism
What is mutualism?
- both species benefit from the association
- Obligate= corals have symbiotic algae(zooxanthellae)
- Facultative=oxpecker feed off ticks and fly maggots on the skin of buffalo
What is commensalism?
- one species benefits; the other appears unharmed
- barnacles on whales=barnacle= gets to areas with more food while whale not harmed, but no positive effect either
What is parasitism?
- one species in the relationship benefits, the other harmed
- Ectoparasites
- lampreys on fish
- parasitic isopod (crustacean)
Endoparasites
-cestode tapeworms in vertebrates
brood parasites
=cuckoos on other birds
What are parasitoids?
- some animals(mostly insects) are parasites in the larval form, but not as adults= Parasitoids
- parasitoids flies and wasps lay eggs inside other animals (hosts), their larvae then eat hosts from within
- only parasites at some of their life
- usually larvae stage is parasitic
Do parasitoids display manipulating behaviour?
- when infected it protects the unhatched wasps larvae= they change her behaviour somehow, when they hatch she dies
What is predation?
-another form of interaction where one species benefits at the expense of the other
-prey evolve traits to avoid being caught by predators
=run faster
=develop defences (e.g. shells, toxins)
=become better at hiding (e.g. camouflage)
=deception (eg. mimicry)
these are adaptations- characteristics of an organism that has evolved because it provides a survival benefit to that organism
How about parasites and evolution?
-species evolve means to avoid parasites
-improved immune system or means of removing parasites
-behavioural adaptations (such as avoiding possible areas of infections)
=eg. kangaroos avoid grazing on grass with kangaroo faeces present= so the don’t get parasites in their gut
=blue tits line their nests with aromatic herbs to deter parasites
What is a counter adaptation?
- the predator or parasite will evolve means to overcome the prey defences
- cuckoos have evolved egg mimicry to fool their hosts
- fox runs faster
- both species have to continue evolving in response to each others’ counter adaptations =have to keep running to stay in the same place= Evolutionary arms race!
What is the evidence of arms races from the fossil record?
- size of herbivore (ungulates) and carnivore brains in the fossil record
- both herbivore and carnivore brain sizes increase over time
- carnivore brain size is always relatively larger and “ahead”
How do evolutionary arms races end?
-One side wins= can drive the other to extinction (smallpox virus) the other side for whom winning is less important drops behind
-Both sides reach a stable optimum= they evolve the optimum strategy they can afford
-They don’t= the arms just keep on changing
-The Ultimate Red Queen scenario
third scenario= most readily observed in nature
What is co-evolution?
-evolutionary arms races are an example of coevolutuion
-evolutionary change in one species influences evolutionary change in another species
eg. orchids that mimic female wasps(visual and chemical)
= orchid phylogeny mirrors wasp phylogeny
=as a wasp species evolve, it’s orchid mimic has evolved with it
-not all coevolution is an arms race eg. Fig wasps pollinate figs, they develop in fig fruit, when females emerge they pick up pollen, females move to a new fig tree with pollen, fertilise new fruits and lay eggs
-fig phylogeny mirrors wasp phylogeny
What is competition?
- if there is a limited supply of a biologically important resource (eg. food, habitat, mates), there will be competition
- competition results in the evolution of characters which make individuals better at competing (eg. enormous body size in male elephant seals)
- competition may take place between individuals of the same species= intraspecific competition
What is Interspecific competition?
-competition between two or more species
eg.
-coal tits feed on outer branches, willow tits inside
-on trees without yellow tits, coal tits feed inside as well
-removal of willow tits has the same effect
-willow tits competitively exclude coal tits
= result is niche separation=differentiation
What is a niche?
-describes the position a species has in a community (the way it makes its living in a community)
What are the evolutionary consequences of interspecific competition?
- if two species with the same niche overlap (exist in sympatry) then there will be competition
- result may be a behavioural change so that there is niche separation
- alternatively there may be a change in physical characteristics (character displacement) so that there is niche separation
What happened with Darwin’s finches?
- character displacement
- medium ground finch (Geospiza fortis) had range of beak sizes
- In 1982 a new species with a big beak (Geospiza magnirostris) invaded the island
- after a drought in 2003, G. fortis evolved much smaller beaks, to avoid interspecific competition with G. magnirostris
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