An Introduction to Ecology

1. An Introduction to Ecology

2. DEFINITIONS ECOLOGY is the study of the relationships between different organisms and their environment A POPULATION is a group of individuals of the same species living in a given area A COMMUNITY is a group consisting of all of the members of all of the populations of different species living in a given area An ECOSYSTEM consists of the living members of a community as well as the abiotic factors that influence these individuals.

3. Population Ecology

4. Population size (N) refers to the number of individuals that make up the gene pool Immigration and Births increase N Emigration and Deaths decrease N

5. Exponential Growth Equation dN/dt = riN Where: d = change, N = number of individuals in population, t = time, dN/dt = the rate of change of N/unit time ri = the intrinsic rate of increase.

7. Is this type of growth realistic ? over the short term – possibly over the long term - NO because the increasing numbers of individuals cause a decrease in the resources available for each individual and there is an increase in the waste products eventually to a toxic level. Thus density dependent factors will eventually affect the population and there are two possibilities: (1) crash, or (2) a leveling off of growth

9. Human population growth

10. “It took from the beginning of time until about 1927 to put the first 2 billion people on the planet; less than 50 years to add the next 2 billion people (by 1974); and just 25 years to add the next 2 billion (by 1999).” “Human Population: The Next Half Century” Joel E. Cohen (Rockefeller University & Columbia University)

12. A shanty town in Manila

13. Rate of current growth http://www.census.gov/main/www/popclock.html

14. Logistic growth takes into account the density dependent factors that regulate population growth and the concept of a carrying capacity (the population size at which stabilization occurs) dN/dt = riN (K - N/K) Where: K = carrying capacity.

16. Is this type of population growth realistic? Not really as a smooth leveling off But with a bumpy line reflecting slight increases over and decreases below K

17. Community Ecology deals with the study of the members of the different species that co-occur in a given area. The scope of the study is usually defined by the researcher

18. Factors that influence the structure (the species composition) of communities include: 1. abiotic factors 2. the availability of resources 3. the ability of the species to respond to changes (adaptability) 4. interspecific interactions (symbiosis, predation or parasitism, commensalism, and spiteful) 5. overall patterns and history

19. Possible interspecific interactions Mutualism ++ Predation or parasitism +- Commensalism +0 Spiteful --

20. Mutualism Sea anemone & clown fish giant moray eel & Labroides

21. Predation and Parasitism Ringneck snake eating salamander

22. Commensalism Shrimp hitchhiking on fire urchin

23. Spiteful Try to think of examples of spiteful interactions between members of two different species

24. NICHE Each of the species that are present have a niche which is the role that they play in their ecosystem Two species cannot occupy the same niche without one of the species (the superior competitor) driving the other species to extinction. This was demonstrated in the lab by Gause Notice then that it is important for the existence of mechanisms that result in niche separation in order for species to coexist

25. Competition occurs when individuals of the same or different species use a limited resource. Although competition can be intraspecific (between members of the same species), interspecific competition is of interest in many studies of community ecology. For example, Robert MacArthur studied niche partitioning in warblers. These birds are very similar with similar needs and in order to reduce competition each species lives in different microhabitat of the same species of tree. MacArthur’s study was basically observational so it is possible that factors other than competition could have resulted in this habitat partitioning.

26. Niche

27. Predator-prey interactions Predators and their prey are obviously interacting. In some cases predators may play a role in the regulation of prey populations. Predation is “good for” the predator but “bad for” the prey. Thus prey have evolved defenses such as crypsis, fleeing, mechanical barriers, chemical deterrents & mimicry (Batesian: harmless mimic and Mullerian: harmful mimic).

29. Crypsis

30. Aposematic coloration

31. Batesian mimic

32. Mullerian mimic

33. Posturing (the very toxic rough skinned newt of the PNW)

34. Over time the community will change (as it ages). Succession is the pattern of colonization of an area where successional stages are sequentially replaced by new stages, basically changing from simple to complex 1. Primary succession occurs in areas that were previously devoid of life 2. Secondary succession occurs when some perturbation results in the return of the community to an earlier stage

35. Primary (1o) Succession Starts with area devoid of life (e.g., after a glacier retreats)

36. Secondary (2o) Succession Occurs when area is exposed to some perturbation that takes it back to an earlier successional stage (e.g., hurricane)

37. Ecosystem Ecology Now we are dealing with the biotic and the abiotic factors that interact within a given area Common characteristics of different ecosystems 1. all have primary producers 2. all have consumers 3. all have detritovores and decomposers 4. all have food chains or more realistically food webs 5. all have biogeochemical cycles through which nutrients move and thus these nutrients are transferred from the environment to organisms and then back to the environment