1. Interactions Within Communities
SBI4U

2. Communities Populations (one species) do not live in isolation
Community: all populations in a given ecosystem at a given time (i.e. many species)
Many organisms in communities work together for survival and could not exist on their own (e.g. insects pollinating flowers)

3. Ecological Niches
Ecological Niche: an organism’s biological characteristics, including use of and interaction with abiotic and biotic resources in its environment (e.g. what it eats, what eats it, the way it reproduces, the temperature range it tolerates, its habitat, its behavioural responses, and any other factors)
Fundamental Niche: the niche an organism would occupy if resources were abundant and there was no competition with other species
Realized Niche: the niche actually occupied by an organism under real conditions

4. Interspecific Competition
Interspecific competition: the interactions between individuals of different species for an essential common resource that is in limited supply
(remember, intraspecific is between individuals of the same species)
Interference competition: actual fighting over resources
Exploitative competition: consumption or use of shared resources

5. Interspecific Competition cont’d
The strongest competition occurs between species whose niches overlap (e.g. tree swallows and bluebirds over a birdhouse; lions and tigers over prey)
Resource partitioning: a way for species occupying the same niche to avoid or reduce competition, by occupying different ecological niches (e.g. two barnacle species occupying a different portion of rocks along the shore)

6. Predation
Predator-prey relationships can have a significant effects on the size of both populations, and can cause population sizes to cycle or fluctuate
When prey populations increase, there is more food for predators so their population might grow, but as predator population increases, the prey population decreases. Gradually, there is less and less food for the predators, so their population decreases, meaning the prey population can begin to increase again.

7. Predator-Prey populations

8. Defense Mechanisms
Plant and animals species have evolved defense mechanisms through repeated encounters with predators over time
Plants use morphological defenses (barbs, thorns, etc.) and chemical defenses
mustard plants contain oils that smell terrible and make them toxic to some insects
balsam fir produces a chemical that mimics an insect growth hormone, and causes linden bugs to remain in their juvenile form and die

9. Defense Mechanisms cont’d
Some predators have evolved to outsmart the defense mechanisms of plants (e.g. cabbage butterfly caterpillars can break down the mustard oils)
Insects often use chemicals from food they eat to make themselves distasteful to predators (e.g. monarch butterfly)

10. Defense Mechanisms cont’d
Animals use both passive defense mechanisms (e.g. hiding) and active defense mechanisms (e.g. fleeing)
Other strategies for animals:
behavioural defenses (e.g. alarm calls)
camouflage
visual warnings (e.g. bright colour means poison)
mimicry (look like another species that actually is poisonous, for example the Viceroy butterfly looks like a monarch)

11. Symbiosis Symbiosis means “living together”
It refers to a relationship in which two individuals of two different species live close together, often touching, and at least one individual must benefit
Three types:
1) Mutualism
2) Commensalism
3) Parasitism

12. 1) Mutualism A symbiotic relationship in which both organisms benefit
Examples:
bacteria live in the guts of ruminants (sheep, cows, deer) and help them digest plant products like cellulose, and get nutrients in return
Oxpecker birds feed on the back of grazing animals, protecting the animal from parasites

13. 2) Commensalism
A symbiotic relationship in which one organism benefits and the other is not affected (some biologists argue that these types of relationship do not exist)
Example:
Remora fish attach themselves to sharks with suction disks, save energy by not swimming, and are able to feed on small pieces of the shark’s prey

14. 3) Parasitism
A symbiotic relationship in which one organism benefits while the other is harmed
The vast majority of parasites cause little or no significant harm to their hosts (makes sense, because it would mean harming the environment on which their health relies)
Examples:
malaria
tapeworms
lice

15. Disruption of Communities
A variety of disturbances can affect the equilibrium of an ecosystem or community in drastic ways
Examples:
natural disasters
introduced exotic species