Lecture XX: Community Ecology Flashcards
What is a community?
All of the populations of all of the species that occupy the same area.
Community ecologists study the interactions between populations of different species within a given area.
Describe the interactions between species:
All species within a community are interconnected. When there is a shift in population size of one species the whole community is affected in some way.
Interactions between species can be beneficial or detrimental
Interspecific interactions (what is it and types):
Interactions between 2 different species within a community.
Types: 1. Competition (-/-)
2. Predation (+/-) 3. Herbivory (+/-) 4. Symbiosis - Parasitism (+/-) - Mutualism (+/+) - Commensalism (+/0)
Competition (-/-)
We have learned about competition between individuals of the same species (intraspecific). Competition for resources: food, water, territories, etc…
However, populations of a species are not alone in their environment, they usually have to compete with individuals of other species as well.
Interspecific Competition: When individuals of different species compete for a resource that limits their reproductive success. This has a negative impact on both species.
Two types of competition:
Individuals can compete in 2 ways: Interference Competition (physical intimidation) or Exploitation Competition (consume as much resource as it can before the other.)
Competitive Exclusion:
In a controlled experiment, if 2 species are competing for the same resource, the species that is inferior at acquiring it will be eliminated from the community.
Ecological Niche
Total use of biotic and abiotic resources in the environment by a species.
Flamingoes feed on small mollusks, crustaceans, and vegetable matter.
Resource partitioning.
If species have the same food source their ecological niches are overlapping. They can coexist as long as there are some other differences in their niches. Ability to coexist under these circumstances often results in: Resource Partitioning
ex. Same food source, but species hunt in different locations within the ecosystem. Therefore they can coexist.
Subdefinition of ecological niche: Fundamental and Realized Niche.
Every species has a fundamental niche, which is the potential niche that they could inhabit if there was no competition for resources.
However, that is rarely the case, so the niche that they actually fill is called their realized niche.
Character Displacement
Changes in phenotypic traits that occur when 2 species coexist and share the same resources.
Both species will experience increased natural selective pressures leading to shifts in phenotype.
Example: When two finch species share the same area their average beak depths become different, they acquire food of differing size.
Predation (+/-)
One species benefits (the predator) and the other loses (the prey)
Adaptations: Claws, sharp teeth, poison, stingers, speed, keen senses etc..)
Prey Adaptations: Alarm calls, quills, armour, camouflage, forming a group, poison…
Types of “camouflage”
Crypsis: Camouflage
Aposematism: stand out against the surroundings. Usually found in poisonous species, a warning to predators.
Types of Mimicry
Batesian Mimicry: A non-poisonous species mimics a poisonous one in appearance and sometimes behavior to scare predators away.
Mullerian Mimicry:
Two or more poisonous or unpalatable species (related or unrelated) resemble each other. Reinforcement of mental image for predators not to eat them.
Herbivory (+/-)
One species benefits (primary consumer; herbivore) by eating the other (photoautotroph; plant or algae)
Plant Adaptations:
Plants have evolved many adaptations to deter herbivores from consuming their tissues:
Thorns, hairs, toxins
Herbivore Adaptations
Herbivores have adaptations to help them digest the tough cellulose cell walls of plants.
Multi chambered stomach, flat teeth, coprophagy: eating feces.
Many herbivores that specialize in eating one type of plant have developed tolerances to toxins found within them.
Types of Symbiosis
- Symbiosis
Parasitism (+/-)
Mutualism (+/+)
Commensalism (+/0)
Symbiosis: Parasitism (+/-)
Parasites feed off of their hosts and therefore benefit from this association. The host provides the parasite with nutrients and is negatively affected by the parasite’s presence.
Symbiosis: Mutualism (+/+)
In a mutualistic symbiosis both species benefit in some way.
Example: Mycorrhizal fungi live in the root tissue of some plants. They provide inorganic nutrients (e.g. N and P) to the host plant and get organic nutrients (sugars) in return.
Defensive Mutualism
Defensive Mutualism
One species receives food or shelter in return for providing protection
Symbiosis: Commensalism (+/0)
One species benefits from the association and the other is unaffected.
Clown fish benefit from the stingers surrounding the anemone they live in as they deter predators. The anemone is unaffected by the clown fishes presence.
Co-Evolution
Species involved in interspecific relationships often co-evolve. For example, a predator and prey will be in an evolutionary arms-race to outcompete the other.
Important Species in a Community
The Dominant Species Most common (abundant) species in a community.
e.g. Maple trees in eastern Canada
What makes them dominant?
Better at acquiring resources than other species
Better able to tolerate predation, disease and/or environmental conditions
What happens when a dominant species is lost?
When a dominant species is lost as is the case with the American chestnut tree due to a fungal disease, other species in the community are drastically affected.
Seven species of moths and butterflies went extinct with the American chestnut trees.
Keystone Species:
A species that may not be abundant, but exerts a strong influence on the community.
Sea otters eat sea urchins that feed on kelp forests. Without the otters the urchins consume the kelp forests quickly.
Killer whales in the 1990’s started to eat otters due to a shortage of their usual food causing a rise in sea urchin populations and large consumption of kelp.
Community Succession.
When there has been a severe environmental disturbance in an area a new community structure will arise and will change in a predictable way over time as the area recovers.
The changes in community structure that occur over time are called succession.
Primary Succession
Starting from scratch after a volcanic eruption or glacier retreat.
No soil present
Takes a long time (100-1000 years)
Starts with hardy organisms such as lichens. Then mosses, grasses, shrubs and trees
Secondary Succesion
Succession after a disturbance such as clear cutting a forest or after a fire.
Soil is present
Takes less time (10 to 100 years)
