E8 Flashcards
What is community ecology?
Study of the community level of organisation, rather than a spatially or temporally defined unit. Study of patterns in the structure and behaviour of multi species assemblages. Areas of land and volumes of water have different assemblages of species, in different proportions, doing different things. These communities have properties that are the sum of the properties of the individuals denizens plus their interactions. These interactions make the community more than the sum of its parts - synergistic emergent properties
What does community ecology seek to understand?
Manner in which groupings of species are distributed and the way there groupings are influenced by the abiotic environment and species interactions. Coexisting individuals of a single species possess characteristics that are unique to populations. Activities at the population level have consequences for the next level up s
What are the species that assemble to make up a community determined by?
Habitat species pool - determined by environmental constraints
Ecological species pool - determined by internal dynamics
Geographic species pool - determined by dispersal constraints
How does science at the community level pose daunting problems?
Large and complex database, ecologists search for patterns in the collective emergent properties of the population. Repeated consistencies or groupings of similar growth forms in different places. Or repeated trends along different environmental gradients. Scales and hierarchies.
What can a community be defined at?
Any scale within a hierarchy of habitats, broad patterns on a global scale, finer scale more subtle patterns. Scale appropriate for investigation depends on the question being asked
What is species richness and how can it be calculated?
Total number of species, requires skilled taxonomists, only a subsample is counted, number of species then depends on number of samples / volume of habitat sampled. Most common species represented first, increasing sample size adds rarer species to the list, sampling stops when a plateau of species richness has been reached, therefore a appropriate number of subsamples to represent the community have been taken
What are diversity indices?
Consists of species richness and abundance, in closely defined communities counts of individuals of each species may suffice, if we are interested in all the animals in a woodland their disparity in size means simple counts would be misleading, biomass per species per unit area.
What is simpsons index (diversity indices)? Watch video on Simpson’s index
Defined in three ways. First step is to calculate Pi, the abundance of a given species divided by the total abundance of species in an area. 1) Simpsons index (probability that 2 randomly selected individuals belong to the same species) 0-1, higher D - lower diversity. 2) simpsons index of diversity (probability that 2 randomly selected individuals belong to different species) 0-1, higher value - higher diversity 1-D. 3) simpsons reciprocal index - value starts at 1, higher value - higher diversity, maximum value is the number of species in the sample 1/D.
What is Shannon-weiner diversity index (diversity indices)? Watch video on Shannon-Werner diversity index
S = total number of species in community
Pi = the proportion of the ith species
Similar to simpsons as its uses species richness and abundance.
Measures uncertainty in predicting the species identity of an individual that is taken at random
What are rank abundance diagrams?
Provide a more complete picture of species abundance and distribution within a community . Each species ranked (1 being the most common). Proportion of each individuals plotted against rank
What are community patterns in space?
Communities do not always have sharp boundaries, rather they occur along gradients. Altitude, moisture, salinity, light
What did case study- ancient woodland transect survey, parc-le-breos, Gower look at?
Quadrats placed every metre along the transect, plant species richness recorded, red-far red photon fluence measured. A gradient of light quality from woodland ride, through woodland edge, into the woodland. Plant species sampled in 20 Quadrats along the woodland transect
How are community patterns in space put into classification?
Assumes communities consist of discrete entities, groups communities that are similar.
What is ordination in terms of community patterns in space?
Allows communities to be organised on a graph so that those most similar in species composition and abundance appear closest together, those that differ considerably are placed further apart, can plot samples or species
What the problems which arise in relation to boundaries in community ecology?
They are often blurred, there are ecotones which are transition zones. Aquatic and terrestrial boundaries appear sharpened, but frogs and otter frequently cross. Many aquatic insects spend their larval lives in the water and their adult lives in the air/on land. On land, sharp boundaries occur between vegetation types on acidic and basic rock types, or where serpentine rocks are juxtaposed, still minerals leach across and boundaries become blurred.
