BIOL 4120: Principles of Ecology Lecture 15: Community Structure

1. BIOL 4120: Principles of Ecology Lecture 15: Community Structure Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

2. Case study: Global Change Invasive plant species, the role of herbivores and Meta-Analysis Wide spread of invasive species: lack of natural enemies (no predators, parasites, pathogens) Results are not conclusive. John Parker, Georgia Tech Question: How native and introduced herbivores affect the abundance of native and introduced plants. Papers: 63 studies Herbivores: bison, deer, rabbits

3. One specific study of the herbivores: Pampas grass (an introduced species to CA) and native jackrabbits John Lambrinos, University of California Exclude rabbits decreased grass survival to 60%, allow grazing decreased the survival to 5%. Grazing of invasive species by native herbivores decreased survivorship.

4. What do the results of the meta-analysis tell us? • What invasive plant spp encounter matters (escape of native herbivores at home, but face new generalist herbivores that they have not evolved defense) • Native species survive better with native herbivores (co-evo) • Single study can’t reveal this information, as only native or invasive spp used.

6. BIOL 4120: Principles of Ecology Lecture 15: Community Structure Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu

7. Outline (Chapter 18)Community structure 15.1 A biological community is an association of interacting populations 15.2 Measure of community structure include numbers of species and trophic levels 15.3 Feeding relationships organize communities in food webs 15.4 Food web structure influences the stability of communities 15.5 Communities can switch between alternative stable states 15.6 Trophic levels are influenced from above by predation and from below by production

8. 15.1 A biological community is an association of interacting populations

9. Two contrasting views of the community Community is defined as groups of species that occupy a given area, interacting with each other directly or indirectly. How important are these interacts? Two reviews Organismal (or discrete or holistic) concept: Clements Individualistic (or continuum) concept: Gleason

10. Organismic (Holistic) concept: Distribution of species is discrete (associations) Association: a type of community with • relative consistent species evolved together; • a uniform general appearance; • a distribution that is characteristics of a particular habitats such as hilltop or valley Transitional between communities are narrow, with few species in common (Ecotone) Suggest a common evolutional history and similar foundational response and tolerances for component species Mutualism and coevolution play important roles in the species that make up association.

12. Individualistic (or continuum) concept: Relationship among co-existing species is the result of similarities in their requirements and tolerances, not the result of strong interactions or common evolutionary history. Gradual change in species abundance along environmental gradient (no associations) Transitions are gradual and difficult to detect.

13. Two views of community Organismic and individualistic views Holistic (discrete) or continuum Ecotones Closed or open communities

14. Ecotones Ecotons are places where many species reach the edges of their distributions Locate: sharp physical differences separate distinct associations

15. Differences in soil conditions may result in ecotones Serpentine soil: soil with high Mg and asbestos, greenish, brownish.

16. The distributions of plant species may be determined by factors other than their physiological tolerance of soil characteristics Plant species are restricted to particular soil in nature does not mean that their distributions are determined solely by their physiological tolerance of soil characteristics. Competition McMillon 1956, California

17. The continuum concept and gradient analysis Twelve tree species occur together in associations in eastern Kentucky But none of them have the same geographic range. At any spot, not form a closed community Limits: north and south, Temperature West and east: precipitation Environmental gradients Continuum concept.

18. Gradient analysis Abundance of each species is plotted on a continuous gradient of one or more environmental factors. The dominant tree species of the Great Smoky Mountains show distinct but overlapping distributions

19. Many gradient analyses have revealed open community structure

20. 15.2 Measures of community structure include numbers of species and trophic levels Biological structure of a community is defined by the mix of species, including both their number and relative abundance. Attributes of community structure Species richness: number of species that occur within the community Relative abundance: counting all individuals of each species in a number of sample plots within a community and determining what percentage each contributes to the total number of individual of all species.

21. Tropic rain forests in Amazon (a), Malaysia (b), and Northeast Australia (c) High net primary productivity (NPP) High diversity of plant and animal life 7% land surface, >50% plant and animal species 10-km2 contain 1500 species of flowing plants and 750 tree species. Richest area in Malaysia, 7900 species 90% of all primate species live in the tropical rain forest All trees, shrubs and saplings on 1 50-hectare plot on a 16-km2 island in Panama include 300 spp among 240,000 individuals (dbh>1cm). This number exceeds all tree species found in Canada.

22. Tropical forests harbor the greatest species richness of any communities Autotrophic Heterotrophic Primary producer Primary consumers Secondary consumers Guild: groups of species that feed on similar resources, have similar ways of life. (leaf eater, stem borer, root chewer etc.) Trophic levels

23. 15.3 Feeding relationship organize communities in food webs Food web An abstract representation of feeding relationships within a community. Food chain Grass  grasshopper  sparrow  hawk A series of arrow, each pointing one species to another, representing flow of food from prey to predator.

24. Food webs describe species interactions Food web: Involve numerical food chains meshed together. Hypothetical food web: Circle: species Links: arrows from one to another Basal species: feed on no others, but are fed upon by others Intermediate species: feed on others, and are fed upon Top predator: not subjected to predator, but prey on other species. Trophic levels

25. A food web for a prairie grassland community in the midwestern US

26. Effects of species richness on food web structure Intertidal mud flat Plant-insect-parasitoids 7 spp 8 species 7 links 12 links One omnivory spp 5 omnivory

27. Species richness and food web complexity Pitcher plants communities in different regions (Indian Ocean) Increasing species richness is associated with increasing food web complexity. Source of food: A: live insect B: dead insect C: organic debris

28. Effect of food web structure on species diversity Robert Paine, University of Washington Sea stars on the community species richness Some species play more important role in a community than others Removing top predator reduced species richness

29. Effect of food web structure on species diversity John Terborgh, Duke University Predator “remove” experiment, rain forest, Venezuela Dam, water rising, form small islands (0.29-09 ha), too small to support predators of large herbivores (howler monkey, green iguanas) Population density: Monkey 20-40 vs 1000 /km2 amerdillo disappeared ants: 4-28 colonies vs <1 /4-hectare  Influence forest regeneration, decreased productivity and diversity declined (136 m-2 to 39).

30. Recap • Two views of biological community (organismal and individualistic; closed and open; discrete and continuum) • Ecotone and Gradient analysis • Community structure (species richness and relative abundance) • Food web and food chair and stability of community

31. Keystone species (consumer) Consumer species that maintain diversity among resource species and thereby influence the structure of a community Insecticide use (over 8 years) killed carysomelid beetle, goldenrod Solidago became dominant and shaded out other species.

32. A variety of food web types Food webs can be distinguished into different types Connectedness web: emphasize feeding relationships among species, portrayed as links in food web Energy flow web: connections between species are quantified by the flux of energy between a resource and its consumer Functional web: influence on the growth rate of other species population.

33. Three types of food web Limpet Sea urchin Chiton Chiton Limpet

34. Case study: Indirect effect: Fox predation on seabirds transforms plant communities on a subarctic island Without fox With fox Fox predate on sea birds, less moved to lands and transfer less nutrients Soil fertility and plant production drop, and landscape shift from grassland to forb- and shrub-dominated lands

35. 15.4 Food web structure influences the stability of communities Some consumers are keystone species and play an important role in community structure. How about the food web structure on stability of communities? Stability: constancy and resilience Constancy: a measure of ability of a system to resist change in the face of outside influences (resistance) Resilience: ability of system to return to some reference state after a disturbance. Resilience means that system may have internal processes that can compensate for disturbance-induced changes. For example, increase in birth rate can help population move back after a population size decreases.

36. Environmental perturbation can cause a delayed response in the functioning of a community Suttle and Thomsen (Mary Power lab at UC Berkeley) Spring watering: Enhanced biomass, especially in the beginning How about species richness? Suttle et al. Science 2007 Any extension of the rainy season resulting from climate change is likely to lead to a reduction of specie richness?

37. Resilience of communities increases with diversity Algae, bacteria, protozoans, rotifer (4 trophic) Lab microcosms (small water bottle, two nutrient levels) Grow 3 weeks, then remove 90% of organisms Resilience: daily rate of return to control biomass level Chris Steiner et al., Rutgers Uni. 2006 High productivity, resilience differ little among low, medium and high diversity

38. 15.6 Communities can switch between alternative stable states Resiliency means that a system is able to return to a “reference” state following a perturbation. Sometimes, however, a system can have more than one stable reference state. Predation and prey: upper and lower equilibrium states of prey population Stable state: small perturbations are followed by return to the reference state Biological community might have multiple stable states: Two keystone species respond differently to climate change: Global warming may shift the community to species favors warming climate Rainfall  tree grow, dry->fire  grassland community structure. (shrubland  grassland)

39. Remove of organisms in a New England rocky intertidal zone community resulted in replacement by one of several possible new community Northern exposure site dominated by brown alga Southern exposure site by another barbacle Replaced original ones and did not recover over five years

40. 15.7 Trophic levels are influenced from above by predation and from below by production The Earth is Green: Hairston, Smith, Slobodkin (1960): “carnivores depress the population of herbivores that would otherwise consume most of the vegetation” Trophic cascade: When the indirect effects of consumer-resource interactions extend through additional trophic levels of a community. Top-down control: when higher trophic levels determine the size of trophic levels below Bottom-up control: when the size of trophic level is determined by the rate of production of its food resource

41. Trophic structure of a community may be determined by bottom-up or top-down control Cases for bottom-up, top-down control or both

42. Mathew Leibold, Uni. Of Chicago 1997, Survey Remove or add herbivore will influence primary production But consumer production is related to primary production Leibold et al. 1997

43. Community structure and its response to changes in productivity depend on the number of trophic levels (Hansson et al. 1998) Hansson et al. Uni. Of Lund in Sweden Tanks 3 or 4 levels Two nutrient conditions Inorganic nutrient

44. Another nice example to demonstrate the indirect interactions A tropic cascade from fish to flowers Fish have indirect effects on the populations of several species in and around ponds Knight et al. 2005, Nature Compared ponds contain fish compared to ponds without fish 4 control (no fish) 4 treatment (within fish)

45. Presence or absence of fish influence dragonfly density

46. The presence or absence of fish also influence the near terrestrial communities Effect on pollinators Pollinators paid more visit to a common plant species that lived on the edges of ponds with fish.

47. Fish have indirect effects on the populations of several species in and around ponds

48. The concept of community revisited Two views of community: organismal (holistic) view and individualistic (continuum) view Clements’s Organismal community is a spatial concept: variety of plant and animal species interacting and influencing the overall structure Gleason’s Continuum view is a population concept, focusing on the response of the component species to the underlying features of the environment. An example (demonstrate two views)

49. An example of forest zonation Topographic distribution of forest communities in the Great Smoky Mountains National Park (west-facing) OH: red- oak-pignut hickory OCH: chestnut oak-chestnut heath OCF: chestnut oak-chestnut forest ROC: red oak-chestnut H: Helmock forest; P: pine; F: Frazir fir; SF: spruce-fir; S: Red spruce; GB: grassy balds HB:Heath balds

50. Patterns of co-occurrence for 4 plant species on a landscape along a gradient of altitude