Community diversity Flashcards
How did Charles Elton describe a community in 1927?
not mere assemblages of species living together, but closely-knit communities or societies comparable to our own.
How did Robert Whittaker describe a community in 1975?
an assemblage of populations of plants, animals, bacteria and fungi that live in an environment and interact with one another, forming a distinctive living system with its own composition, structure, environmental relations, development and function.
How did Robert Rickleaf describe a community in 1990?
the associations of plants and animals that are spatially delimited and that are dominated by one or more prominent species or by a physical characteristic (no mention of interactions)
Give the common definition of a community
A group of organisms belonging to a number of different species that co-occur in the same habitat or area and interact through tropic and spatial relationships
Give the common definition of community ecology
the study of patterns and processes involving at leave 2 species at a particular location
What is species relative abundance?
the percentage of each species contributing to the total number of individuals of all species
What do the results of Simpson’s index indicate?
1 = low diversity 0 = high diversity
Define a disturbance
an event that changes a community, removes organisms from it, and alters resource availability
What are the 2 types of community disturbances
physical disturbances and biotic disturbances
Define a keystone species
a species that has a disproportionately strong influence within a particular ecosystem, such that its removal results in severe destabilisation of the ecosystem and can lead to further species losses.
Give an example of a mutualistic keystone species
cleaner wrasse
Define a guild
a group of species that depend on the same resource for survival and reproduction
Define a functional group
a group of species that performs the same function within the ecological community (e.g. grazers, predators)
Describe community interactions of a dung beetle
over 7,000 species in the same guild, but with 3-7 distinct functional groups: dwellers, tunnellers and rollers
What is a foundation species?
the dominating species, with a great abundance or biomass, affecting community structure.
Give an example of a dominant/foundation species
a spruce tree in tiaga/borreal forrests
How do you measure community importance of a species?
by the change in the community trait (e.g. the species richness, productivity of producers, abundance of functional groups etc) per unit change in the abundance of the proposed keystone species.
What is the equation for calculating the total impact of a species?
community importance x proportional abundance or biomass the the community
How do you calculate the direct connectedness of a food web?
number of links / number of species (S)^2
How do you calculate the connectivity of a food web?
(2(number of links) / (S(S-1)) )x100
Describe the basic structure of a food web in term of functional levels
basal species eaten by numerous intermediate species, which are then eaten by a top predator
Give 3 example of indirect community interactions
trophic cascades, indirect commensualism, apparent competition
Give an example of indirect commensualism
beavers gnaw on tree stumps, which changes the chemical composition of their sprouting leaves, providing better nutrition to the leaf beetles feeding on them.
Give an example of apparent competition
Brassica nigra grass provide cover for small herbivorous mammals (e.g. mice), which in turn reduces the density of Nassella pulchra
What does it mean by ‘species interaction strength’?
the strength of a link between two species in a food web
Give 2 ways you can measure a species interaction strength?
finding out the % prey of the stomach content, or exclude the predator from the community and observe the effects in prey abundance
Give the 3 basic trophic levels of a simple community
producers, grazers and predators
Give an example of top-down control
Distribution of wolves influence elk movements in Yellowstone National Park
What effects the distribution of wolves in YNP?
elks (prey), cougars (competition), coyotes (interference competition)
Give an example of bottom-up control
grasslands in new mexico consist of 2 trophic levels: plants and rodents. After 10 years without rodent, there’s no effect on plant population, but a change in rainfall has a strong effect, suggesting bottom-down control.
