Struggle for Existence pt. 7 Flashcards
ecological community
all organisms or biotic entities in some spatially defined locality
ecosystem
biotic + abiotic (atmosphere, weather, mineral nutrients) elements
Community study
Considers only a subset of the species in a local ecosystem. Subsets might be taxonomically-defined or functionally-defined.
What does it mean for organisms to share a guild?
Have similar functional niches.
Community ecology is concerned with
species richness
dominants
species that are very common in a community
species diversity
distribution of abundance and rarity
ex. a community with ten equally abundant bird species is considered more diverse than one with one common bird species and 9 rare ones
What does the brake term in logistic model represent?
intraspecific competition
What does the second braking term in Lotka-Volterra competition model represent
interspecific competition exerted by a second species
What is the alpha parameter and what does it represent?
competition coefficient, effect on 1 by 2
ON-BY
Four possible outcomes according to Lotka-Volterra model
- species 1 can outcompete 2 making it go extinct and it will reach carrying capacity OR VICE VERSA
- two species can stably coexist
- competition is unstable but winner depends on starting numbers, whichever one gets initial advantage will outcompete other
Condition for stable existence…
that each species inhibit its own population growth more than it inhibits the growth of the other species’ population.
G. F. Gause
investigated competition with various species of protozoan genus Paramecium (showed behaviour that resembled LV predictions)
Thomas Park
Flour beetle experiments. Showed importance of abiotic factors in determining outcome of biotic interactions. Confirmed that it was unlikely of difficult for two competing species to coexist.
Principle of Competitive Exclusion
Two species that compete for the same resources cannot coexist for long
Robert MacArthur
Warbler study
niche overlap=alpha competition coefficient
(later this was proven to be an incorrect assumption except in specific environment with to K species)
however it was found later on that OVERLAP DOES NOT MEASURE COMP.
Limiting similarity
max amount of niche overlap that would allow two species to coexist (out of date idea)
What community structure arises from a “resource-partitioning” viewpoint?
Equilibrial, because it says coexistence depends on patterns of resource use and that competitive exclusion will sort out organisms until only ones with different niches remain
What does it mean when a cycle damps out or becomes amplified?
damp out
- predator and prey level off asymptotically at stable values and coexist indefinitely
Amplified
- mutual extinction
Do predator prey lagged cycles actually exist in the lab
not really, and if they do, it doesn’t persist for long.
How prey persists
- finding refuge (nooks and crannies)
- multiple prey species
Predator-prey cycles are most pronounced in….
- simple communities with low species richness where predators have little choice
- predators are obligate specialists that can successfully consume only one species of prey
Where can we see pronounced long-lived predator-prey cycles in real life?
- Arctic
- with herbivorous insects (frequently eat only one kind of plant because they’ve adapted to the chemical defences of that plant)
How does predation affect interspecific competition?
It can stop superior competitors from outcompeting inferior competitors. It keeps competition for resources from reaching an equilibrium state.
Robert Paine
sea star experiments
- when the starfish were removed biodiversity went down because mussels proliferated (biotic factors)
- in calm waters, mussels survived better because they weren’t being scraped off by debris slammed against rock from turbulent water (abiotic factors)
Why are predators, parasites, and diseases especially effective mechanisms for driving populations below their carrying capacity?
Because they are density-dependent control factors. The more abundant the prey, the more efficient the natural enemy.
metapopulation
collection of numerous smaller subpopulations spread across space (regions contain numerous discrete patches of habitat)
equilibrium proportion of patches occupied (equation)
p = 1 - (e/c)
source-sink dichotomy
- source patch maintains a growing subpopulation and is a net exporter of dispersing colonists
- sink patch is lower quality and incapable of maintaining subpop. except through immigration (if dispersal were cut off the sink patch would go extinct, but if it is embedded in a healthy metapop, it can remain occupied indefinitely)
emergent properties
Attributes of the whole system that are not inherent in the individual parts of the system (whole is greater than the sum of its parts)
coexistence can be…
global but not local. The differences in life histories allows prolonged coexistence at the metapopulation level.
