Ch 52: Community Ecology Flashcards
biological community
all the populations of interacting species living within a defined area
Commensalism
occurs when one species benefits but the other species is unaffected (+/0)
Competition
occurs when individuals use the same resources—resulting in lower fitness for both (−/−)
Consumption
occurs when one organism eats or absorbs nutrients from another, increasing the consumer’s fitness but decreasing the victim’s fitness (+/−)
Mutualism
occurs when two species interact in a way that confers fitness benefits to both (+/+)
EX of commensalism
epiphytic orchid grows on a tree host
-uses its excess sap as nutrients
Intraspecific competition
same species
density dependent
Interspecific competition
occurs when members of different species use the same limiting
can be direct or indirect (ex of indirect: species eats food while destroying food source of another’s)
Niche
range of resources and conditions that species can tolerate
EX: Paramecium
when both species of bacteria put together, their carrying capacities decreased (forced to share food/resources)
However, eventually the weaker species (P.Caudatum) declined dramatically and starved (could not compete)
Competitive Exclusion principle
When superior species uses all the resource space of its competitor, the inferior competitor will disappear
Fundamental niche
total theoretical range of environmental conditions that a species can tolerate
Realized niche
portion of the fundamental niche that a species actually occupies, given limiting factors such as competition with other species (smaller)
How did J.Connell test the Competitive Exclusion Principle?
He removed one of the competitors and observed the response by the remaining species
EX: competitive exclusion of Chthamalus barnacles from the lower intertidal zone by Semibalanus barnacles
Chtalamus lives in upper tidal
Semibalanus in lower
Chthamalus do not occur in the lower intertidal zone b/c they are outcompeted by Semibalanus
Fitness trade-off
an inevitable compromise in adaptation
If individuals are extremely good at competing for a particular resource, they are probably less good at enduring drought conditions, warding off disease, or preventing predation
Herbivory
consumption of plant or algal tissues by herbivores
Predation
killing and consumption of most or all of another individual (the prey) by a predator
Endoparasites
live inside a host’s body and are usually simple and wormlike
ex:tapeworms
Ectoparasites
live outside of hosts and typically have adaptations for harvesting fluids from hosts
ex: ticks & mistletoe
Parasitoids
free living as adults but have endoparasitic larvae. Parasitoidism is almost always fatal to hosts
Constitutive/standing defences
list
defences that are always present and include
–Cryptic colouration and object resemblance
–Escape behaviour
–Toxins and other chemicals
–Schooling and flocking
–Defence armor and weapons
Constitutive Defences
Grasshopper EX
resemblance to a leaf enables this grasshopper to escape detection
mimicry
the close resemblance of one species to another
Batesian mimicry
when nontoxic prey species resemble dangerous prey species. One species benefits
Müllerian mimicry
when two harmful prey species resemble each other. Both benefit
inducible defences
traits produced in response to the presence of a predator
EX: Are mussel defences induced by the presence of crabs?
Average shell thickness is significantly higher downstream in the presence of crabs.
Mussel increase investment in defence when they detect crabs; shell thickness is an inducible defence
How can parasites ensure that they get to new hosts?
EX: nematodes
Nematods infect ants -have red end that looks like a berry, therefore eaten by birds
Nematods need birds to complete their life cycle
Mutualisms are dynamic
EX: treehoppers
Treehoppers are small insects that feed by sucking the sugar out of the phloem of plants. They secrete honeydew from their posteriors. Ants harvest the honeydew for food
Do we see mutualism between ants and treehoppers?
TH benefit only when spiders are common. Ants benefit more when spiders are rare
Key attributes of community structure (4):
- The total number of species
- The general types and outcomes of interactions among all species
- The relative abundance of those species
- The physical aspects that matter -including abiotic factors (size or altitude gradient) and biotic factors (physical structure provided by the dominant vegetation type)
food chain
Multiple consumption interactions linked
food web
A summary of some or all of the consumption interactions in a community
Multiple food chains combined
Bottom-up influences
from plants/algae up the food chain
-amount of nutrients, sunlight, water, etc. determine abundance of primary producers
Top-down influences
consumer limits prey pop
ex: wolves don’t tolerate coyotes; coyotes eat mice, so mice—and then hawk—populations have increase
Ecosystem engineers
Not only serve as primary producers but also create physical structure that provides habitat for other organisms
Ex: beavers dam streams, making habitat for aquatic animals like frogs and turtles
Trophic cascade
When change in top-down influencers cause clear effects 2-3 links away on food web
Disturbance
any strong, short-lived disruption to a community that changes the distribution of living or nonliving resources
A disturbance’s impact is a function of three factors:
- Type of disturbance
- Frequency of disturbance
- Severity of disturbance
EX: Giant sequoia shows damage after a fire..
through their growth rings
- trees withstand many fires within its lifetime and regrow their bark around burned
In Primary succession…
organisms colonize bare mineral soil (e.g. volcanic ash, land slide)
In secondary succession…
soil is already present, so recovery is faster than primary succession
Early successional communities are dominated by species that…
–Are short lived
–Are small in stature
–Disperse their seeds over long distances
Late successional communities are dominated by species that…
–Long lived
–Large
–Good competitors for light and nutrients
Facilitation
existing species help those that arrive
Tolerance
existing species do not affect the arrivals
Inhibition
presence of one species inhibits the success of another
species richness
number of species present in a given community
species diversity
weighted measure that incorporates a species’ relative abundance