Community Ecology BDC331

1. 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

2. Species A Species B Species C Species D Species E Species F Species G Species H Species I Species J Performance or Abundance Environmental Gradient e.g. Temperature 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

3. 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

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

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

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

7. Mutualism + + Commensalism + 0 Predation + - Amensalism - 0 Competition - - Inter-specific Interactions Species A Species B Outcomes of interactions between two species

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

9. 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 A number of other trophic based units also used

10. Taxocene

11. 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

12. Morpho-species

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

15. How small is a community?

16. Habitat Selection – Habitat Species Pool Inter-specific Interactions Dispersal Ability – Geographic Species Pool Determinants of Community Composition and Structure Physiological Constraints Historic Events Evolutionary Processes Regional Species Pool 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

17. Local Community

18. 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 Local Community Niche model for Coelacanth Regional Species Pool

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

20. Inter-Specific Interactions Local Community

21. Equilibrium or non-equilibrium communities? B2 Equilibrium Communities Remain stable* (in balance) within environmental range B1 A1 within range X-Y Community Attribute Stable communities show strong biological interactions, high levels of density dependence. A2 A1 C Range of Environments X Y Z * Time it takes to recover from disturbance; variability over time; persistence Equilibrium Non-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

22. 1 – physically defined communities Assemblages of species found in a particular place or habitat Identifying or Delineating Communities ARTIFICIAL?

23. Great Smoky Mountains Tennessee 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. 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 SUBJECTIVE?

24. 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

25. 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. 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.

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