Lecture 9/10 Plant and Animal Interactions Flashcards
Types of symbiosis (5)
Mutualism: All species involved benefit from the interaction
Commensalism: One Organism benefits and the other is neutral
Competition: One Organism benefits and the other is Harmed
Amensalism : one species causes harm to another organism without any cost or benefits to itself
Parasitism : duh
Types of herbivores (4)
Grazers – consume plant parts (mostly green) near the substrate, e.g., snails graze algae, geese graze grass
Browsers – consume plant parts (mostly green) well above the substrate, e.g., deer browse the leaves of shrubs and saplings
Frugivores – consume fruits, often without damaging the seeds within, in which case the relationship is likely to be mutualistic
Granivores – seed “predators”
Plant - Herbivore interactions (main interaction, +3 pros and cons)
- Short growing season Limits plant growth & reproduction, which Limits herbivore growth & reproduction
Heavy exploitation of plant species by herbivores can:
– Decrease abundance of plants
– Destroy insulating moss layers
– Change plant communities
- However, herbivores also
– Defecate, adding nutrients
– Alter competition regimes between plants
– Disperse seeds
Ecosystem Engineers (3)
Definition: an organism that modifies, creates or destroys habitats
* modulates the availability of resources to other species, causing physical state changes in biotic or
abiotic materials
ex: Moose browse of deciduous trees and shrubs on Isle Royale (Lake Superior) caused shift to spruce-
dominated forest
HSS hypothesis (Why is the earth Green) (3)
Carnivores : No predators, limited only by food source
Herbivores: Limited by predation
Producers: Limited by competition and resources (not herbivory)
Since producers only competition is more producers = green world
Trophic Cascade Definition
influence of producers or consumers on species that are two or more trophic levels away
Top-Down control
influence of predators on the relative abundance of lower trophic levels
ex: Sea otters promote kelp growth by hunting sea urchins, the kelp’s main herbivore
Bottom-up control
influence of producers on the relative abundance of higher trophic levels
Population Cycle
a pattern of periodic fluctuations in population size with rather constant period (amplitude may vary highly)
Features of population cycles (5)
- periodic
* fluctuations recur repeatedly - regular
* hare & lynx: 8 – 11 years - large amplitude
- northern distribution
* northern populations cycle more frequently than
southern - synchronous
* broadly synchronous within and among species
Delayed density dependence
As populations grow, there is a time lag until negative feedback mechanisms bring the population back down
Hare - Lynx cycle (2)
- Hares use up food when population densities are high, then starve → decline in lynx population
- Lynx reach high density in response to increases in hare density; at high density, eat all the hares & hare population crashes
hares limit lynx (bottom-up regulation)
or
lynx limit hares (top-down regulation)
Effects of Predators on prey (2)
Density-mediated: predators reduce prey numbers
* may be more common in aquatic systems
Trait-mediated: predators affect prey phenotype (e.g.,
behavior)
* effect of the risk of predation
Ecology of Fear (2)
Non-consumptive predator effects
*Altered foraging patterns (behavior)
* Chronic stress under risk of predation (physiology)
Exploitation ecosystems hypothesis (EEH) (2)
Effects of trophic cascades usually alternate by trophic level
Primary productivity determines the number of trophic levels in an ecosystem
