Mark J Gibbons, Room 4.102, BCB Department, UWC Community Ecology BDC331 Mark J Gibbons, Room 4.102, BCB Department, UWC Tel: 021 959 2475. Email: mgibbons@uwc.ac.za Image acknowledgements – http://www.google.com

Environmental Condition Some Definitions Environmental Condition Physical environmental variable or factor, that varies in space and time, and to which organisms respond Examples include: Temperature, salinity, moisture, elevation, depth, nitrogen concentration of water, beach grain size etc etc etc Environmental Gradient e.g. Temperature Performance or Abundance Species A Species B Species C Species D Species E Species F Species G Species H Species I Species J

Resource Something that is required or used by an organism, the quantities of which can be reduced by the organism Examples include: Dissolved oxygen, sunlight, water, carbon dioxide, mineral nutrients, organisms as food

Population A group of individuals of the same species that coexist in space and/or time

Characteristic of intra-specific competition Population size / density Rate Birth Death K Born Population size / density Numbers Dying Difference = NET Recruitment N - Shaped K S-Shaped Growth Curves Characteristic of intra-specific competition

Community? A group of interacting populations of different species that coexist in time/space

Inter-specific Interactions Competition Inter-specific Interactions Species A Species B + Mutualism + Commensalism - + Predation - Amensalism Outcomes of interactions between two species

A group of interacting populations of different species that coexist in time/space A community as viewed from a predator-prey perspective

Community subsets Guild Communities can have very many interacting populations of different species and to study all of them requires a suite of expert taxonomists at the very least. Community ecologists tend to get around this issue by studying subsets of the community Community subsets Guild A number of other trophic based units also used

Taxocene

Dominant species – abundance or biomass Easy to work with – common Can work across Guilds as number of taxa lower Quantitative errors reduced – common Assumed to play an important role within community

Morpho-species

How big is a community? ANY SCALE Broad patterns in terrestrial vegetation can be recognized at the global scale - BIOMES

How small is a community?

Determinants of Community Composition and Structure Physiological Constraints Historic Events Evolutionary Processes Regional Species Pool Habitat Selection – Habitat Species Pool Dispersal Ability – Geographic Species Pool Inter-specific Interactions Local Community Rules – a species will only be present if: It can disperse there Conditions and resources allow it to survive Predators and competitors etc don’t preclude it

Local Community

Regional Species Pool Evolutionary Processes Local Community Evolutionary Processes Physiological constraints – Warm water species will not survive variable, and sometimes low temperatures experienced Historic Events – Tectonic events have separated species that could coexist but which don’t Niche model for Coelacanth Regional Species Pool

Regional Species Pool Habitat selection – Habitat Species Pool Dispersal Ability – Geographic Species Pool

Inter-Specific Interactions Local Community

We assume Equilibrium Communities – spp abundance constant wrt time Equilibrium or non-equilibrium communities? We assume Equilibrium Communities – spp abundance constant wrt time Remain locally stable* (in balance) within environmental range - habitat Unstable B2 A1 within range X-Y B1 Stable communities show strong biological interactions, high levels of density dependence. Community Attribute A2 A1 C X Y Z Neutral Range of Environments * Time it takes to recover from disturbance; variability over time; persistence Non-equilibrium Equilibrium Biotic coupling Competition Saturated Resource limitation Density dependence Optimality Few stochastic effects Tight patterns Biotic decoupling Species independence Unsaturated Abiotic limitation Density independence Opportunism Large stochastic effects Loose patterns

ARTIFICIAL? Identifying or Delineating Communities 1 – physically defined communities Assemblages of species found in a particular place or habitat ARTIFICIAL?

Great Smoky Mountains Tennessee 2 – taxonomically defined communities Identified by presence of one or more conspicuous species that dominate biomass and/or numbers, or which contribute importantly to the physical attributes of the community Topographic distributions of the characteristic dominant tree species of the Great Smokey Mountains, Tennessee, on an idealized west-facing mountain and valley BG, beech gap; CF, cove forest; F, Fraser fir forest; GB, grassy bald; H, hemlock forest; HB, heath bald; OCF, chestnut oak-chestnut forest; OCH, chestnut oak-chestnut heath; OH, oak-hickory; P, pine forest & heath; ROC, red-oak-chestnut forest; S, spruce forest; SF, spruce-fir forest; WOC, white oak-chestnut forest. Great Smoky Mountains Tennessee SUBJECTIVE?

3 – statistically defined communities Sets of species whose abundances are significantly correlated, positively or negatively, over space and/or time. Look at numerical and specific composition of samples Determine similarities between samples Look for a pattern in the similarities between samples And so identify communities OBJECTIVELY

4 – interactively defined communities Subsets of species in a particular place or habitat, whose interactions influence their abundance. Only some, and perhaps none, of the species in a physically defined community may constitute an interactively defined community. Hairston (1981: Ecology, 62: 65-72) noted that of the seven species of plethodontid salamander in his study (North Carolina, USA), only the two most common influenced each others abundances: the balance, while ecologically similar, remained unaffected by each others abundance.

THE END Image acknowledgements – http://www.google.com