Population - Community Composition Patterns Flashcards
What are populations influenced by?
Space and time by biotic and abiotic factors
What does community assembly derive rom?
Dispersal Contraints
Envrionmental Constraints
Internal dynamics(Competition, predation, facilitation)
Two classes of internal dynamics…
Selection is the determinsitc interactions between competitors or predators and prey
Drift is the random changes in species relative to abundances
What are the four classes of community assembly described by Vellend?
Ecological Drift
Selection
Speciation
Dispersal
Communities on the macro scale…
Biomes with broad patterns by climate, like temperatre forests
Communities on the micro scale?
Communities of species, like beech and maple, or gut biome of species.
Hypervolume
Space in more than three dimensions.
What is a hypervolume in ecology?
Multi-dimensional resource space avaiable to and used by organisms
Most basic way of characterising communties?
Counting species present, allowing comparison by richness.
Sampling in comparing seperate communities…
If multiple sample taken, variable should be the same
Rarefaction
The reduction in the density of something.
How can richness be worked out?
Comparing number of species to number of individuals in a sample
Simpsons Diversity Index
A measure of diversity taking into account number of species present, as well as relativev abundance of each species.
Why is it important to take into acount rarity and commonness of species?
A population dominant in one species may have same richness as another if both have 10 total species.
What does simpsons index account for?
Abundance and species richness.
What does simpsons index measure?
Proportion of individuals contributing to the total in the sample
Hill Numbers
Describe the effective number of species or species equivalents
What three functions can be used to measure species richness
Alpha Diversity
Beta Diversity
Gamma Diversity
Alpha Diversity
Describes species richness occuring within a given area within a region, smaller than the entire distribution of the species
Beta Diversity
Rate at which species richnesss increases as one moves in a straight line across a region from one habitat to another habitat
Gamma Diversity
Describes the species richness within an entire region.
Mathematically describe a,b,g diversity…
G is sum of B and A, if each patch has identical species list then B=0 and A=G, and B contributes to G when heterogeneity arises.
Rank Abundance Diagrams
These display relative species abundance of a variety of P1, from an abundance rank 1 to however many species there are.
Down side of RAD?
Do not account for HOW species interact with one another
Niche Orientated Models
Help in understanding of mechanisms of community organisation.
Types of Niche-Orientated Models
Dominance Pre-emption model
Random Fraction Model
Dominance Decay Model
Dominance Premption Model
Describes situations where after intial colonisation, each new species preempts more than 50% of the smallest remaining niche.
Random Fraction Model
A situation where abundances of different species are not mutually related at all
Dominance Decay Model
Where invading species occupy the niche spaces of the current most abundant species.
What do niche-orientated models provide?
Abstract on commmunity structure of a given indicie(diversity, richness, equitability)
Community Size Spectra
This represents a specific function(BMR, reproduction, specialisaiton, tolerance, diet) relative to abundance.
Why is community size spectra good?
Relative size of individuals indicates many functional traits and ecological processes.(competitiveness, vulnerability and reproduction)
Monotonic
Variable in such aa way that it never increases nor decreases
Gradient Analysis
Technique analysing dynamic, structure of functional change in ecosystems
Whittaker Gradient Analysis…
Great smokey mountains of changes of vegetation with varying altitude gradients.
A criticisms of gradient analysis…
Bias in detecting patterns and subjectiveness of gradient chosen, most approparatie to a particular species not necesserality appropriate ubiquitously.
Ordination
This is a mathematical treatment allowing community organising in a graph so those most similar in species composition and relative abundance appear closer together
How can bias in Gradient Analysis be avoided?
Using CCA
Canonical Correspondence Analysis
Ordination technique determining axis from the response data as a linear comibnaiton of measured predictors
Use of CCA in ecology?
Extracts gradients deriving composition of ecological communities.
Example of CCA?
Rotifer assessed by eutrophication(CP levels, P conc and phytoplankton cell transparency)
CCA allows for…
Measure of species compositon against a variety of envrionmental factors.
Correlation does not imply causation in CCA…
Dissolved oxygen and community composition may vary together by a common response to other envrionmental factors.
Temporal community structure change analysis…
Fire prone trees where composition relfective of time since a fire was prominent.
Clements view on population…
Superorganism like tissues
Modern view of populations…
A gradient analysis and ordination indicating physical characteristics of a given location will unlikely occur with another group of species under different conditons elsehwere…
How may species vary temporally?
Incapable of reaching a location.
How may species vary temporally?
Incapable of reaching a location.
Inapproprate resource and conditions
Preclusion of competitors, predators and parasites
Example of common temporal change?
Life cycles with seasonal changes, with changes in ecosystem structure.
What are vellends four class of community assembly?
Dispersal
Niche Assembly
Neutral Assembly
Historical Assembly
Neutral Assembly
This describes stochastic processes like birth, death and dispersal, without paritcular environmental factors influencing species co-existence.
Hypervolumes
These are multi-dimensional shapes with each axis being some environmental variable: temperature, precipiration or soil nutrients.
What does space occupied by a species represent in a hypervolume?
Conditions they can persists for ecological niche determination and what limits distribition/abundance.
How might Hypervolumes be simplified?
Principal Component Analysis and Non-metric Multidimensional Scaling.
What is a reduced hypervolume analysed by?
Convex hulls
Convex Hulls
This is the minium convex set enclosing them all, yielding a polygon connecting the outermost points in the sample and all whose inner angle are less than 180 degrees.
What is an example of using Convex Hulls in ecology?
Quantifying functional traits of plants and how they relate to envrionmental conditions, like leaf area and specific leaf area across different environmental gradients.
What can Artifical Neural Networks be used for?
Prediction of new data it hasnt seen before by training, like on environmental variable relation to species occurence
Artifical Neural Networks
This simulates biological nervous systems where information is sent via input signals to a processor resulting in output signals.
What is an example of functional application of ANN?
Analysis of 66 bird species in Switzerland with envrionmental variables like previous bird occurence data, trained ANN to predict probabilty of occurence in new area.
Simpsons Diversity Index
This index is a biodiversity measured based on richness and eveness of a community.
How is the SDI calculated?
Proportions of each species are squared then summed, then subtracting that sum from 1.
What does a high SDI indicate?
Greater dominane of one or a few species.
Why is SDI useful?
Takes into account number of species present in a community and relative abundance of each species.
What is a downside of SDI?
It is influenced heavily by rare species.
How can the simpsons diversity index be applied to conservation?
Before and after restoration efforts to assess effects of restoration.
Rarefaction
This is a species richness estimation based on number of individuals or samples collected from the community.
What is the process of rarefaction?
Random sub-sampling of a given number of samples is taken, where unique species in that subsample are taken.
This is repeated, each subsample being a different set of samples, until maximum unique species observed is reached
Hill Numbers
These quantify number of species and their relative abundances.
What are hill numbers based on?
More even species distribution in the community is the more diverse the community.
First-order Hill Number
This measures species richness by counting number of species in the ocmmunity.
Second-order Hill number
This is the same as the Shannon index.
Shannon Index
This is a measure of the information content(like relative abundance) of a communtiy rather than of the paritcular species that is present.
What is a disadvantage of first-order hill numbers?
Do not take into account abundance, thus two communities with same species number might have different overall diversity.
How do A, B and G mathematically relate?
G = A x B, meaning low beta means gamma and alpha are more equal, or where high beta means gamma greater than alpha.
How is Beta Diversity measured?
Jaccards Index
Bray-Curtis Dissimilarity.
Jaccards Index
This gauges similarity and diversity of sample sets (J = a/ (a+b+c)
What do rank abundance diagrams do?
Quantify relative abundaces of different species within a community.
How are RAD graphs read?
If curve is steep, community dominated by few highly abundant species.
