Ecological Interactions and Community Dynamics: Understanding the Web of Life

1. A community’s interactions include competition, predation, herbivory, symbiosis, and disease • Populations are linked by interspecific interactions that affect the survival and reproduction _

2. Table 53.1 • Interspecific interactions • Can have differing effects on the populations involved

3. Competition • Interspecific competition occurs when two species compete for a particular resource that is in short supply • Intraspecific competition is competition between members of the same species

4. The Competitive Exclusion Principle • Gause’s competitive exclusion principle • States that two species competing for the same limiting resources cannot coexist in the same place

5. Ecological Niches • The ecological niche is the organism’s role in that ecosystem. This includes it’s: • Spatial habitat or where it lives • Interactions with other species • Niche rule -

6. Fundamental niche is the entire range of conditions an organism is potentially able to occupy within an ecosystem • Realized niche

7. The niche concept allows restatement of the competitive exclusion principle • Two species cannot coexist in a community if their niches are identical

8. However, ecologically similar species can coexist in a community

9. As a result of competition • A species’ fundamental niche may be different from its realized niche

10. Predation • Since all species are preyed upon during some stage of their life, mechanisms of defense against being eaten have evolved in every species • These mechanisms evolve through natural selection

11. Feeding adaptations of predators include • Claws, teeth, fangs, stingers, and poison • Animals also display • A great variety of defensive adaptations • These include mechanical defenses such as a porcupines quills, horns, antlers or chemical defenses such as a skunk’s odor or the poison of some frogs

12. Cryptic coloration, or camouflage • Makes prey difficult to spot

13. Aposematic colorationwarns predators to stay away from prey that possess chemical defenses

14. Mimicry • In some cases, one prey species may gain significant protection by mimicking the appearance of another

15. In Batesian mimicry • A palatable or harmless species mimics an unpalatable or harmful model

16. In Müllerian mimicry • Two or more unpalatable species resemble each other

17. Herbivory • Herbivory, the process in which an herbivore eats parts of a plant • Has led to the evolution of plant mechanical and chemical defenses and consequent adaptations by herbivores • Chemical defenses include toxins such as strychnine, morphine, nicotine, tannis, and poison oak and poison ivy

18. Symbiosis • Symbiosis is an interaction between two or more species in which one species lives in or on another species

19. Parasitism • In parasitism, one organism, the parasite benefits by deriving its nourishment from another organism, its host, which is harmed in the process

20. Parasitism exerts substantial influence on populations • And the structure of communities

21. Disease • The effects of disease on populations and communities

22. Pathogens, disease-causing agents • Are typically bacteria, viruses, or protists

23. Mutualism • Mutualistic symbiosis, or mutualism • Is an interspecific interaction that benefits both species

24. Commensalism • In commensalism • One species benefits and the other is not affected

25. Commensal interactions have been difficult to document in nature

26. Dominant and keystone speciesexert strong controls on community structure • In general, a small number of species in a community

27. Species with a Large Impact • Certain species have an especially large impact on the structure of entire communities

28. Dominant Species • Dominant species • Are those species in a community that are most abundant or have the highest biomass

29. Keystone Species • A keystone predator may help to maintain diversity in a community by reducing the numbers of the strongest competitor in a community-this helps to prevent competitive exclusion of weaker competitors, and prevent strongest competitor from becoming too dominant

30. Field studies of sea stars • Exhibit their role as a keystone species in intertidal communities

31. Observation of sea otter populations and their predation

32. Ecological Succession • Ecological succession is the sequence of community and ecosystem changes after a disturbance • Succession occurs because of modifications to the physical environment produced by the community itself • Climate affects,but is not the cause of succession

33. Primary succession • Occurs where no soil exists when succession begins • Secondary succession

34. Primary Succession • Volcanic islands, glaciers cause primary succession • Lichens, mosses are the first large, photosynthetic organisms to colonize the barren ground • These are called pioneer species or communities-the first communities to establish themselves on newly formed habitats

35. Lichens decompose thin layers of rock, as they die and decompose they leave behind organic matter, which is the beginning of soil

36. Soil develops gradually as organic matter accumulates from the decomposed remains of the early colonizers • Once soil develops, grasses, shrubs, trees replace lichens and mosses as seeds are blown in or carried in by animals

37. Retreating glaciers • Provide a valuable field-research opportunity on succession

38. Succession on the moraines in Glacier Bay, Alaska • Follows a predictable pattern of change in vegetation and soil characteristics

39. Secondary Succession • Occurs where a disturbance has destroyed an existing community but left the soil intact • Clear cut forests, abandoned farms are causes • Occurs much quicker, because soil is already present, and the roots and seeds of plants may already be present • Climax communities are the permanent final stage of succession

40. Succession • Soil contains organic matter or humus which is good for plant growth. Soil accumulates from the death and decay of plants and animals • As more soil builds up, larger plants can grow, their roots help to prevent the erosion of soil • Eventually, decomposers recycle nutrients from the plants and animals that live and die there

41. Sampling & Fisheries Management

42. Random Sampling • To determine the population size of organisms, ecologists take a random sample of a population a use it to estimate the total number of organisms

43. The Quadrat Method • Quadrat is a square of a certain size • Organisms within randomly selected quadrats are counted and these counts are used to determine the population size

44. Using the quadrat method to determine the population size of plants in an ecosystem • Map area • Determine quadrat size • Place numbered grid over map • Use random number table to select quadrats to be sampled • Count number of organisms within each sample quadrat • Multiply the average number of organisms by the total number of quadrats to get estimate of population size

45. Capture-Mark-Release-Recapture Method • Sampling technique used to estimate the number of animals in an ecosystem

46. Capture members of population and mark them • Release marked animals • Capture second sample, count number of marked and unmarked individuals • Use equation: Number marked in second sample (n3) = number marked in first sample (n1) Total caught in second sample (n2) size of whole population (N) Population size (N) = (n1 X n2) / n3

47. Limitations to mark-recapture method • Marks may injure animals • Marks may make them more susceptible to predation

48. Estimating size of commercial fish stocks • Study catches made by fishermen • Type of fish, age, size, breeding conditions • Gather information from fishermen • Fish released, tagging, questionnaires, review logs • Sample populations using trawling nets

49. Determine ages of fish population to determine if population is shrinking from lack of spawning (few young) or overfishing (few old)

50. Maximum sustainable yield • Highest proportion of fish that can be removed from total population without jeopardizing future populations