BISC 204
Other types of interactions
1. Positive indirect effects
a. Trophic cascade: benefits alternate between tropic levels
-Killer whale, sea otter example (Estes et al. 1998)
2. Commensalism: species interactions where one species benefits, the other is unaffected
-often structural or support based
ex. barnacles on whales
ex. scavengers following predators
3. Mutualism: positive species interactions where both species benefit
*Very common, and sometimes species pairs are highly specialized (co-evolved symbiosis)
a. Trophic: complementary acquisition of resources
-Examples: mychorrhizae and plants
b. Defensive: one species provides a protective function in return for energy/nutrients
-Examples: anemone fish and anemone
ant – acacia
c. Dispersive: organisms receive energy in exchange for dispersing gametes/propagules (pollen, fruit, seeds)
-Examples: fruit and frugivores
orchid bees and orchids
One mechanism that can produce mutualisms (there are others):
Coevolution (see classic paper by Ehrlich and Raven 1964): Evolutionary change in a trait of species A in response to a trait in species B
-Primarily driven by tight species associations
-Specific (particular traits) and reciprocal (between both species)
-Can be either antagonistic or mutualistic: can manifest as evolutionary “arms races”
Disease & Parasitism
Parasites are extremely common in natural populations/communities.
Parasitism +/- ecological interaction
Parasite-host systems show evolution of virulence and resistance. History alters the effects of parasites on their hosts.
Parasites often have complex life-cycles
requires more than one host to complete life-cycle (each host provides a different ‘environment’)
Definitive host:
Intermediate host(s):
Successful completion of life-cycle requires transmission:
**creates opportunity for strong co-evolution among hosts and parasites
Vertical:
Horizontal:
Direct:
Indirect:
Types of Parasites
Microparasites:
Macroparasites:
Ectoparasites:
examples?
Endoparasites:
examples?
Ecological effects of parasites
Individual-level effects:
types:
examples:
Population-level effects:
types:
Examples:
Community-level effects:
types:
examples: