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Levels of Ecological Organization in Freshwater Systems

This study delves into the levels of ecological organization in freshwater systems, focusing on population, community, and ecosystem dynamics. It investigates the factors that influence species composition, diversity, and the consequences of these variations. Additionally, the importance of biodiversity in freshwater ecosystems is highlighted, alongside discussions on community structure, relative abundance, and diversity indices such as Shannon and Simpson's. Through exploring food webs, functional groups, and trophic levels, the research examines the assumptions underlying community composition and the implications of variation over space and time. The study also evaluates the role of limiting resources and conditions in shaping community diversity, emphasizing interactions with the abiotic environment and among species. Predation, competition, and mutualism are explored as key drivers of community composition, with a focus on trophic cascades and the impact of fish species on invertebrate density and species richness. Lastly, community composition in response to disturbance, productivity, and ecosystem age is analyzed, shedding light on the intricate relationships that shape freshwater community dynamics.

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Levels of Ecological Organization in Freshwater Systems

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  1. Levels of Ecological Organization in Freshwater Systems Population Community Ecosystem

  2. What controls species composition (aka, diversity)? • What causes species composition to change over space and time? • What are the consequences of variation in species composition? • Why does “biodiversity” matter in freshwater systems? Community Ecology in Freshwater Systems

  3. A group of interacting species occurring in a particular place, at a particular time. What is a community?

  4. How do we describe freshwater communities? • Relative abundance • Species richness • Diversity indices (e.g., Shannon, Simpson’s)

  5. How do you describe a community? • Species richness: 4

  6. How do you describe a community? • Diversity indices: richness weighted • by relative abundance >

  7. Food Webs, Functional Groups, and Trophic Levels Levels ~ Diversity Sp. 10 Sp. 7 Sp. 9 Sp. 8 Sp. 1 Sp. 2 Sp. 3 Sp. 4 Sp. 6 Sp. 5

  8. Assumptions: • Individual species occupy one level Sp. 7 Sp. 6 Sp. 7 Sp. 7 Sp. 5 Sp. 7 Sp. 1 Sp. 2 Sp. 3 Sp. 4

  9. Assumptions: • Individual species occupy one level • These systems are rare: Sp. 3 Sp. 5 Sp. 2 Sp. 1 Sp. 4 Sp. 3 Sp. 2 Sp. 1

  10. Variation in community composition over space

  11. Variation in community composition over time Spring Fall

  12. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • > Limiting resources • > Limiting conditions

  13. Limiting Resources: Some thing a species or group of species uses to survive.

  14. Limiting Condition: Some attribute of the environment that a species or group of species must tolerate to survive in a particular place.

  15. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • > Predation (+ / -) • > Competition (- / -) • > Mutualism (+ / +)

  16. …and galaxiid hell. (Flecker and Townsend 1994) Predation and Community Composition • Trophic cascades

  17. Predation and Community Composition • Trophic cascades No Fish (Flecker and Townsend 1994)

  18. Predation and Community Composition • Trophic cascades • Significant effect of “fish species” on total invertebrate density. • Significant negative effect of “fish” on species richness, no effect of “fish species”. (Flecker and Townsend 1994)

  19. What isn’t insect richness telling us about the effect of trout on community composition? (Flecker and Townsend 1994)

  20. Predation and Community Composition • Super predators!! Fish No Fish

  21. Competition and Community Composition Disruptive selection Proportion of Population Diet breadth • The ghost of competition past

  22. Competition and Community Composition • The ghost of competition past

  23. Competition and Community Composition • The ghost of competition past

  24. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • AND • Interactions among species

  25. Abiotic  Biotic effects on community composition Dicosmoecus “Resistant Grazer” (Wootton et al. 1996)

  26. Abiotic  Biotic effects (Wootton et al. 1996)

  27. = Regulated Unregulated

  28. Abiotic  Biotic effects (Wootton et al. 1996)

  29. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Ecosystem age

  30. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Ecosystem age • Successional ponds • Ephemeral streams and ponds

  31. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Ecosystem age • Disturbance

  32. Disturbance and community composition Good Colonizers + Good Competitors Good Colonizers Good Competitors Minimally Disturbed Extensively Disturbed (Connell 1978)

  33. Disturbance and community composition

  34. Disturbance and community composition Kadashan River Basin, SE Alaska • Response of riparian plant communities to flood frequency. • Frequency = number of times per year that the mean elevation of a site was inundated. (Pollock et al. 1998)

  35. Disturbance and community composition (Pollock et al. 1998)

  36. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Ecosystem age • Disturbance • Productivity

  37. Productivity and community composition VS.

  38. Productivity and community composition

  39. The paradox of enrichment Population Size Time (Rosenzweig 1971)

  40. The paradox of enrichment Low and Moderate Productivity High Productivity Population Size Population Size Time Time (Rosenzweig 1971)

  41. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Age • Disturbance • Productivity • Size and Complexity

  42. Size and community composition Hypothesis: As size increases, so does habitat heterogeneity, resulting in more “niches” that can be filled by more species.

  43. Size and community composition

  44. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Age • Disturbance • Productivity • Size and Complexity ?

  45. Size versus Productivity • Sampled 25 lakes in North America that varied in size AND productivity. • Used N isotopes in top-predators fish to determine food-chain length leading to that predator. 15N < 15N Maximum Trophic Position Maximum Trophic Position < (Post et al. 2000)

  46. Size versus Productivity (Post et al. 2000)

  47. Size versus Productivity (Post et al. 2000)

  48. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Age • Disturbance • Productivity • Size and Complexity ?

  49. What controls community composition (i.e., species diversity)? • Interactions with the abiotic environment • Interactions among species • Age • Disturbance • Productivity • Size and Complexity • Colonization and Extinction

  50. Colonization, extinction, and community composition Island Biogeography Theory (MacArthur and Wilson 1987)

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