BIOL 4120: Principles of Ecology Lecture 16: Community Ecology

1. BIOL 4120: Principles of Ecology Lecture 16: Community Ecology Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Outline (Chapter 17)Factors influence community structure Last, community structure, biological and physical structure What processes shape these patterns of community structure? Why are communities in some environments more or less diverse than others? ??? Last, community structure, biological and physical structure What processes shape these patterns of community structure? Why are communities in some environments more or less diverse than others? ???

3. 17.1 Fundamental niche constrains community structure Plants grow in desert Shade-torlent species For a species to maintain its population, its individuals must survive and reproduce. Certain combinations of environmental conditions are necessary for individuals of each species to tolerate the physical environment, obtain energy and nutrients, and avoid predators. The total requirements of a species for all resources and physical conditions determine where it can live and how abundant it can be at any one place within its range. These requirements are termed abstractly the ecological niche. G.E. Hutchinson (1958) suggested that the niche could be modeled as an imaginary space with many dimensions, in which each dimension or axis represents the range of some environmental condition or resource that is required by the species. Thus, the niche of a plant might include the range of temperatures that it can tolerate, the intensity of light required for photosynthesis, specific humidity regimes, and minimum quantities of essential soil nutrients for uptake. A useful extension of the niche concept is the distinction between fundamental and realized niches (Figure 9g-1). The fundamental niche of a species includes the total range of environmental conditions that are suitable for existence without the influence of interspecific competition or predation from other species. The realized niche describes that part of the fundamental niche actually occupied by the species.Plants grow in desert Shade-torlent species For a species to maintain its population, its individuals must survive and reproduce. Certain combinations of environmental conditions are necessary for individuals of each species to tolerate the physical environment, obtain energy and nutrients, and avoid predators. The total requirements of a species for all resources and physical conditions determine where it can live and how abundant it can be at any one place within its range. These requirements are termed abstractly the ecological niche. G.E. Hutchinson (1958) suggested that the niche could be modeled as an imaginary space with many dimensions, in which each dimension or axis represents the range of some environmental condition or resource that is required by the species. Thus, the niche of a plant might include the range of temperatures that it can tolerate, the intensity of light required for photosynthesis, specific humidity regimes, and minimum quantities of essential soil nutrients for uptake. A useful extension of the niche concept is the distinction between fundamental and realized niches (Figure 9g-1). The fundamental niche of a species includes the total range of environmental conditions that are suitable for existence without the influence of interspecific competition or predation from other species. The realized niche describes that part of the fundamental niche actually occupied by the species.

4. Fundamental niche constrains community structure Gradients: extreme dry to water Cold to hot Gradients: extreme dry to water Cold to hot

5. Distribution of three species

6. Null model How about interactions of species?How about interactions of species?

7. 17.2 Species interactions are diffuse Lecture 12: Chapter 13: Lecture 12: Chapter 13:

8. Species interactions are diffuse Lecture 12: Chapter 13: Lecture 12: Chapter 13:

9. Greens are dominate species Hare Hair Greens are dominate species Hare Hair

10. 17.3 Food webs illustrate indirect interactions Another important feature of food web beside the direct interactions is the indirect interactions between species A species does not interact directly with a species (lynx and white spruce), but it influence a species that does interact directly with this species (snowshoe hare). Another important feature of food web beside the direct interactions is the indirect interactions between species A species does not interact directly with a species (lynx and white spruce), but it influence a species that does interact directly with this species (snowshoe hare).

11. Several of mussel and barnacle species that were superior competitors in the absence of predation excluded the other species, reducing the overall diversity of the community.Several of mussel and barnacle species that were superior competitors in the absence of predation excluded the other species, reducing the overall diversity of the community.

12. Keystone predation Predation can also influence outcome of interactions between prey species The starfish preys on many species of mussels, barnacles, limpets, etc Remove starfish from experimental plots and compare to normal situation Number of prey species in experimental plots was halved Diversity was decreased as better competitors excluded other species Link keystone species concept to Keystone predation Keystone predation describes how predation influence prey competition. Another kind of indirect interactions among species is apparent competition: it�s how add a prey to predator-prey relationshio will influence the predator populationLink keystone species concept to Keystone predation Keystone predation describes how predation influence prey competition. Another kind of indirect interactions among species is apparent competition: it�s how add a prey to predator-prey relationshio will influence the predator population

13. Apparent competition In the absence of predator, the population of each prey is regulated by purely intraspecific density-dependent mechanisms Neither prey species compete, directly or indirectly, with each other Predator abundance depends on the total abundance of prey Under these conditions, the combined population abundance of two prey species will support a higher predator density. Link keystone species concept to Keystone predation Keystone predation describes how predation influence prey competition. Another kind of indirect interactions among species is apparent competition: it�s how add a prey to predator-prey relationshio will influence the predator populationLink keystone species concept to Keystone predation Keystone predation describes how predation influence prey competition. Another kind of indirect interactions among species is apparent competition: it�s how add a prey to predator-prey relationshio will influence the predator population

14. Apparent competition

15. Indirect commensalism Another indirect interactions between species is indirect commensalism (small one can�t compete with large water fleas) What�s the relationships of --, +-? Etc Indirect commensalism Two herbivorous Daphnia spp. and their predators, midge larvae and salamander larvae Salamander larvae prey on large Daphnia Midge prey on small Daphnia Salamander and midge can survive together Midge cannot survive alone Salamander can survive alone Another indirect interactions between species is indirect commensalism (small one can�t compete with large water fleas) What�s the relationships of --, +-? Etc Indirect commensalism Two herbivorous Daphnia spp. and their predators, midge larvae and salamander larvae Salamander larvae prey on large Daphnia Midge prey on small Daphnia Salamander and midge can survive together Midge cannot survive alone Salamander can survive alone

16. Indirect mutualism When indirect interaction is beneficial to both (predator) species. Examples?Examples?

17. Indirect interactions play an important role Removing top predators from community could have some unforeseen consequences (conservation and management) An Example: Predator control in Greater Yellowstone ecosystem (Joel Berger from UN Reno) Predator control, decrease in Grizzly bear and wolf increase in moose population decrease in willow and other woody species along riverline decrease in birds (even local extinction for some species)

18. 17.4 Food webs suggest controls of community structure

19. Difficult to study (there are some dominant species like starfish, but majority is mystery) One approach is splitting species into functional groups Each group has a similar function and perhaps can replace each other Based on the relationships among these functional types, people proposed:Based on the relationships among these functional types, people proposed:

20. Bottom-up control Plant population control herbivore populations, which in turn control the diversity and population density of carnivore population Top-down control Predator (carnivore) populations control the diversity of prey species, and the prey of the prey, and so on. Bottom-up control is very common. Mostly, community structure is regulated by bottom-up control. How is the community regulated? In bottom-up control, the structure of food chains and food webs is controlled (limited) by the productivity and abundance of populations in the trophic level below In top-down control, the predator populations control the abundance of prey species, and the prey of the prey, and so on M. Powers (University of Oklahoma Biological Station) showed that a top predator (largemouth bass) had strong indirect effects that cascaded through the food web to the primary producers (benthic algae) How is the community regulated? In bottom-up control, the structure of food chains and food webs is controlled (limited) by the productivity and abundance of populations in the trophic level below In top-down control, the predator populations control the abundance of prey species, and the prey of the prey, and so on M. Powers (University of Oklahoma Biological Station) showed that a top predator (largemouth bass) had strong indirect effects that cascaded through the food web to the primary producers (benthic algae)

21. Examples support top-down control Large-mouth bass experiment by Mary Power at OU Bass (Predator) prey on minnows (herbivore), minnows graze on algae Remove bass vs control Pools with bass had low minnow population and a luxuriant growth of algae Pools with bass removed had high minnow populations and low populations (biomass) of algae Top predator control plant population indirectly through their direct control on herbivores. �The world is green�: predators will keep herbivores in control If remove some alage, not much influence, is not bottom control; if removal all, no species can support: how to test bottom up control??? Like in forests, if some biomass removed, no influence on hebiviors and caniviors, top-down controlIf remove some alage, not much influence, is not bottom control; if removal all, no species can support: how to test bottom up control??? Like in forests, if some biomass removed, no influence on hebiviors and caniviors, top-down control

22. 17.5 Species interactions along environmental gradients involve both stress tolerance and competition Lecture 12: Chapter 13: Lecture 12: Chapter 13:

23. Figure 17.9The Pacific Madrone (Arbutus menziesii), is a species of arbutus found on the west coast of North America, from British Columbia (chiefly Vancouver Island) to California, mainly in the Pacific Coast Ranges but also scattered on the west slope of the Sierra Nevada mountains. Figure 17.9The Pacific Madrone (Arbutus menziesii), is a species of arbutus found on the west coast of North America, from British Columbia (chiefly Vancouver Island) to California, mainly in the Pacific Coast Ranges but also scattered on the west slope of the Sierra Nevada mountains.

24. Figure 17.12 Spartina (smooth and saltmeadow cord grass, tall and short), Juncus (black needle rush) How to test: remove the lower border species. Fertilization changed the competition ability, less competitive one become more competitive.Figure 17.12 Spartina (smooth and saltmeadow cord grass, tall and short), Juncus (black needle rush) How to test: remove the lower border species. Fertilization changed the competition ability, less competitive one become more competitive.

25. 17.6 Environmental heterogeneity influences community diversity Lecture 12: Chapter 13: Distribution patters: uniform, random, clumped distribution Lecture 12: Chapter 13: Distribution patters: uniform, random, clumped distribution

26. Figure 17.14Figure 17.14

27. 17.7 Resource availability can influence plant diversity within a community Lecture 12: Chapter 13: Lecture 12: Chapter 13:

29. Run a car and ride a bicycle in a crowded street Nutrient serve as a predator in animal world. Low nutrient likes add a predator. Huston hypothesized that the inverse relationship results from reduced competitive displacement under low nutrient availability Other studies have supported this hypothesis White mustard and cress coexisted on less fertile soil (F. Bazzaz and J. Harper) Park Grass experiment � the unfertilized plots are the only ones retaining the original diversity of species planted Run a car and ride a bicycle in a crowded street Nutrient serve as a predator in animal world. Low nutrient likes add a predator. Huston hypothesized that the inverse relationship results from reduced competitive displacement under low nutrient availability Other studies have supported this hypothesis White mustard and cress coexisted on less fertile soil (F. Bazzaz and J. Harper) Park Grass experiment � the unfertilized plots are the only ones retaining the original diversity of species planted

30. What processes cause the decrease in diversity with increasing nutrient availability? J. Cahill (University of Alberta, Canada) examined how competition in grassland communities shifts along a gradient of nutrient availability A shift in the importance of belowground and aboveground competition and the nature of their interaction under varying levels of nutrient availability

31. Competition for belowground and aboveground resources differs in an important way Competition for belowground resources is size symmetric because nutrient uptake is proportional to the plant�s root size Symmetric competition occurs when individuals compete in proportion to their size Competition for aboveground resources is size asymmetric � larger plants have a disproportionate advantage by shading smaller ones.

32. Under low nutrient availability, plant growth rate, size, and density are low for all species Competition primarily occurs belowground ? symmetric Growth rate, size, and density increase as nutrient availability increases As faster-growing species overtop the others, creating a disparity in light availability ? asymmetric competition

33. Fertilization results in an increase in the species richness of autotrophs in both freshwater and marine communities Why the difference between patterns in terrestrial versus aquatic communities? Differences in the role of competition Reduced competition results from fertilization Limited by more than one nutrient, no single spp has a competitive advantage.