Lecture 40: biotic interactions

When does competition arise

Resource limitations

Competitive exclusion principle

If 2 species compete for exactly the same resource, one will survive and drive the other to extinction

Ecological niche

Position of a species within the ecosystem

What is the nice of a species if the habitat it occupies is its address

Its profession

Niche of sloth

Tree- top large herbivore which hide from predators by being slow and blending in with leaves

Fundamental niche

Niche potentially occupied by A species

Realised niche

Niche actually occupied by a species

What may cause difference of fundamental and realised niche

Competition eg. The presence of one barnacle species limits the realised niche of another

Niche differences of barnacle species

• When both are present: chthamalus realised niche at high tide & balanus realised niche At low tide

• When balanus are removed: chthamacus fundamental niche at high & low tide

Competition in terms of time

When common and golden spiny mouse co-exist the common are nocturnal and golden are diurnal but when living separated both are nocturnal

sympatry

Coexisting / living together

allopatry

Living separately

Character displacement

Tendency for characteristics to be more divergent in sympatric populations of 2 species than in allopatric populations of the same two species - thus results in reduced competitions

Character displacement in Galapagos finches beak size

• Similar beak depth of G. Fuliginosa & G. Fortis when living separately

• G. Fuliginosa smaller beak depth when living together

Example of predators shaping behaviour of prey

• Daily vertical migration patterns of zooplankton - dives to deeper water in day to avoid fish

• Predators evolve capture method and prey evolve method of evasion

Evolutionary arms race

When predators evolve better capture methods then prey evolve better methods of evasion

Arms race between bats and moths

• Moths fly at night to avoid predatory birds

• Bats evolve echolocation to fly at night and feed on moths

• Moths listen for but echolocation and either fly erratically, respond with own clicks or drop out of Sky

• Some bats produce quiet clicks when approaching a moth

• Some moths tell difference between searching clicks & fast clicks so only respond to fast ones

How do bats reduce moth capture success

Some produce noise to jam echolocation of other nearby bats

How else can we reduce effect of predators

Swamp them

Where do larval cicadas live

Underground

Larval period of magicicadas

13 or 17 year so predators can't synchronise as it is a prime number

Schistocephalus life cycle

1. Egg shed into water

2. Larva eaten by copepod

3. Copepod eaten by stickleback

4. Stickleback eaten by bird as it feeds nearer open water surface so more likely to be caught

Example of commensalism relationship

Cattle egrets and cattle

Facultative mutualism

Optional e.g. Ants feed on nectar by tree & live in hollow thorns and in return, defend the tree against herbivores & remove competing seedlings

Obligate mutualism

Essential relationship where at least one cannot survive without the other eg. Legume plants & nitrogen fixing bacteria, corals & photosynthesising algae, large blue butterflies & red ants

Mutualism example

Plants develop fruit to and seed dispersal & animals develop preference for brightly coloured plant good

Large blue butterflies & red ant mutualism

Young caterpillar produces smell to attract red ants which take it underground & milk it for honeydew - caterpillar eats ant eggs & larvae I butterfly hatches from chrysalis underground & is guarded by ants as it emerges from surface