1. Interspecific competition
…a form of competition in which individuals of different species compete for the same resources in an ecosystem (e.g. food or living space).

2. What do you see in this picture?

3. Competition
Competition is the active demand between two or more organisms for a resource.
Each competitor is inhibited in some way by the interaction.
Members of the same species of the same age will have similar requirements, so will compete (for resources: food, water, space, mates, breeding grounds) – intraspecific competition.
Members of different species also compete for resources – interspecific competition.

4. What do plants compete for?
Water
Light
Nutrients – minerals
Space
Pollinators
What do animals compete for?
- food
Space/territory
Mate
Alpha status

5. Gause’s Principle (the competition exclusive principle)
Russian scientist G.F. Gause experimented on 3 species of freshwater protists.
One species always out-competed the others, but which one was the ‘winner’ depended on the conditions (eg freshness of water).
Gause concluded that two species cannot share the same habitat indefinitely if they have similar requirements.
This is known as Gause’s Principle, or the competition exclusion principle (no two species can indefinately occupy the same niche in the same habitat).

7. 1: A smaller (yellow) species of bird forages across the whole tree
1: A smaller (yellow) species of bird forages across the whole tree. 2: A larger (red) species competes for resources. 3: Red dominates in the middle for the more abundant resources. Yellow adapts to a new niche restricted to the top and bottom of the tree, avoiding competition.

8. Competition is avoided in nature
Closely related species living together (in sympatry) avoid competition by exploiting different resources.
Example: Grazing animals in the Serengeti
Eat different parts of the grass
Migrate at different times
If niches are similar, competition will be more intense.
Read pg 57 )from ‘For species sharing….’ and outline how sympatric species minimise competition.

9. Succession
This is a progressive change in the make-up of a community in which plant species are replaced as a result of competition.
Two types:
Primary – the first, occur in habitats that are generally unfavourable for growth (unfertile soil). Once established, is now a climax community. Pioneer plants hardy, but weak competitors.
Secondary – soil already fertile (eg after fire). First colonists grow rapidly and produce lots of seeds. Poor competitors for light.
Succession

10. Allelopathy and antibiosis
Allelopathy – production of chemicals that inhibit growth of other species eg Walnut trees, macrocarpas.
Antibiosis – production by fungi of chemicals that kill of inhibit the growth of bacteria.
Both examples of contest competition – actively prevent others from obtaining a resource.

11. Questions to ponder
If an animal in a given habitat has a similar ecological niche to another species, how would direct competition influence their interactions? (Direct competition occurs when individuals compete with each other directly for the same resource - Indirect competition occurs when organisms use the same resource, but don’t necessarily interact with each other).
What possible outcomes could there be if an exotic species is accidentally introduced to a stable, mixed-bird community? (Can you think of NZ examples?)

12. Possible answers
- One could out-compete the other for the resource, leading to decreased population size/possible extinction of species.
Could elicit aggressive responses between species.
Increased stress within groups.
Could effect predator-prey relationships – numbers.
May cause the less competitive species to emigrate.
NZ example –
German wasp/Kaka/Tui/Bellbirds/honeydew insect

13. The behaviour of three native bird species (tui, bellbird, kaka) is known to be affected by wasps removing honeydew.
Several common and widespread bird species have had significant declines in their abundance of the last 30 years; attributable to the impacts of a number of introduced species, but especially wasps.
Tui spend over 80% of their foraging time on honeydew but reduce their feeding on honeydew or leave beech forest when honeydew falls below a threshold level.
Bellbirds remain in the forest on days when the standing crop of honeydew was low, but reduce their time spent feeding and on activities like singing, flying, social interactions and grooming.
The behaviour of kaka also changes when it became unprofitable for them to forage on honeydew.

14. - less resources
- more aggressive/territorial behaviour.
- less reproductive success due to limited resources (of weaker species).

15. Dr. Seuss And NUH is the letter I use to spell Nutches,
Even Dr. Seuss Understood the Complexities of Competition
And NUH is the letter I use to spell Nutches,
Who live in small caves, known as Niches, for hutches.
These Nutches have troubles, the biggest of which is
The fact there are many more Nutches than Niches.
Each Nutch in a Nich knows that some other Nutch
Would like to move into his Nich very much.
So each Nutch in a Nich has to watch that small Nich
Or Nutches who haven’t got Niches will snitch.
Dr. Seuss – On Beyond Zebra (1955)