Direct interactions
Occur between two species.
Competition, predation, facilitation.
Indirect interactions
Relationship between two species is mediated by a third (or more) species
Example of indirect effects with cats and bees
Pollination depends on bees.
Bees depend on mice.
Mice depend on cats.
Therefore increasing cats could impact pollination
Indirect effects often discovered by accident when
When species are experimentally removed to study strength of direct interactions
A tropic cascade example with sea-otters
Indirect regulation of kelp forest by sea otters
Sea otters feed on the urchins that feed on the kelp forests
Trophic facilitation example.
Two plants and an herbivore.
Herbivore eats plant 1.
Plant 2 helps plant 1 to grow more.
Indirectly helps herbivore.
Competitive network vs competitive hierarchy
Competitive network in which no one species dominates.
Competitive hierarchy in which one species dominates the interaction
Two types of networks of interacting species
Competitive network.
Competitive hierarchy.
Strength of species interactions can be measured
Removing one species from community and look at effect on other species
When measuring the strength of species interactions, if removal of interactor species results in a large decrease of target species the interaction is
Strongly positive
When measuring the strength of species interactions, if removal of interactor species results in a large increase of target species the interaction is
Strongly negative
The strength of species interactions is strongly positive when
Removal of interactor species causes a large decrease of the target species
The strength of species interactions is strongly negative when
Removal of interactor species causes a large increase of the target species
Foundation species
Dominant species that has a large effect on other species and species diversity with high abundance or biomass
Foundation species are usually
Primary producers.
Good competitors
Example of Foundation species and why
...
Ecosystem engineers
Create, modify, or maintain physical habitat for themselves and other species
Example of ecosystem engineer and why
Trees.
Provide habitat and food.
Reduce light, wind, and rainfall which changes temperature and moisture.
Examples of ecosystem engineers besides trees
Grasses in grasslands.
Corals on a coral reef.
Mangroves.
Oysters.
Keystone species
Strong effect in community despite low biomass or abundance
Keystone species usually influence community structure indirectly via
Trophic means
Are ecosystem engineers Founder species or keystone species
Mainly founder but some Keystone
Example of a keystone species that is an ecosystem engineer and why
Beavers.
Few individuals have large impacts by building dams
Why are alligators keystone species
Deepen waterways that serve as refuge for other species
Context-dependent species interactions
Interactions change under different environmental conditions
Species Diversity
Species richness and species eveness
Biodiversity
Variety of all forms of life, from genes to species, through to the broad scale of ecosystems
Trophic Cascade
When a predator in a food web suppresses the abundance of its prey, thereby releasing the next trophic level from predation.