1. BIOL 4120: Principles of Ecology Lecture 15: Community Structure
Dafeng Hui
Office: Harned Hall 320
Phone:

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
Bison, deer, rabbits: generlists, eat all type of plants
Unexpected outcomes: (differ from enemy-escape hypothesis):
When the herbivores were introduced, introduced plants were more abundance than the native species
When facing native herbivores, the introduced species were less abundant than the native species.
Importance of coevulationay relatinships in determing how well a species fares in its interaction with antagonists.

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.
Grazing decreased survive of invasive species
Herbivores: generalist, eat all, not selective

4. What do the results of the meta-analysis tell us?
4/16/2017
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:

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
Lecture 12:
Chapter 13:

8. 15.1 A biological community is an association of interacting populations
A ponderosa pine community in Santa Catalina Mountain of Arizona,
A riparian forest borading a stream in South Arizona
A young decidous forest in Great Smoky Mountain of TN
Name the community
Different species: how do they interact with each other? What kinds of interaction do they have? How they are related to environmental factors.
Patterns

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
Interactions among species in a community can have both positive and negative influences on species populations
How important are these interactions in determining community structure?
Two major views — the difference between the views is the importance of interactions, current and evolutionary, in the structuring of communities
Organismic concept of communities
Individualistic or continuum concept

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.
Some textbook call places where associations change: ecotones

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
One important in organiimic view if the ecotone concept.

15. Differences in soil conditions may result in ecotones
‘Serpen tine
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
Dominant plants can reinforce or even create ecotones by altering their environment. Decidous and conniferous (needle leaf, acid; slow decompositionthick layer of organic matter).
Grasslands and shrub or forests: sharp changes in temperature, moisture and light
Pygmu: pijmy Cypress: cIpres
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.
The distribution of species along an environmental gradient is often referred to as the continuum concept.
Continuum concept can be visualized by a gradient analysis, in which abundance of each species is plotted on a continuous gradient of one or more environmental factors.

18. Gradient analysis
Abundance of each species is plotted on a continuous gradient of one or more environmental factors.
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
The individulistic view can be summerized in this figure

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.
How to measure community structure:
Biological structure:

21. High net primary productivity (NPP)
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.
Ecologists count all trees, shrubs and saplings on 1 50-hectare plot on Barro Colorado Island, a 16-km2 island in Gatun Lake, Panama include 300 spp among 240,000 individuals (diameter>1cm). This number exceeds all tree species found in Canada.
Plots of only one heactare in some an Amazonian Peru and Ecuador contain more than 300 species; every other individual tree in such a plot belongs to a different species.
Tree m tall, some 55 m or so

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
One simple way to partition species is with respect to their feeding relationships
Each species can be placed on one of several tropic leves.
Tropic level: feeding relationships within community

23. 15.3 Feeding relationship organize communities in food webs
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.
Lecture 12:
Chapter 13:

24. Food webs describe species interactions
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
A, basal; H herbivores C, carnivores;
Trophic level: group of species that derive food energy in a similar way
P link to itself means cammona;os, (feeds on itself): salmador feed on salmandor, mite feeds on mite
Trophic (in greek, nourishment)
Ominovours: feed on different levels

25. A food web for a prairie grassland community in the midwestern US
Direct and indirect influences; mechanism controlling the community structure (discuss next chapter)
Weasel crow
A food web for a prairie grassland community in the midwestern US

26. Effects of species richness on food web structure
We can rank complex of food web by feeding links and tropic level
Increase in food web complexity is usually linked to species richness, links and trophic levels.
4 or 5 omnivores?
Intertidal mud flat Plant-insect-parasitoids
7 spp species
7 links links
One omnivory spp 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
Guilds? It’s not clear how the consumer seeks foods
Links per species=?
Shows increasing ecological diversity (more trophic levels and guilds within each trophic level) and longer food chains, but similar numbers of feeding links per species.
A: live insects; B: recently drowned insect; c: older 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 ( ha), too small to support predators of large herbivores (howler monkey, green iguanas)
Population density: Monkey 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).
Compared as no to mainland, as no predators to monkey, its density increased from to 1000 per km2.
Amerdillo disappeared, so ant and other leaf eaters pop increased.
Small saplings: decreased from per m2 to as few as 39 (average 136).

30. 4/16/2017
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
Like fertilizer apply. Low nutrient conditions, no species can grow very well and shade out others. If fertilized, goldenrod will grow better.
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.
Based on the relationship among species (different ways in which species influence one another within the community)

33. Three types of food web Limpet Sea urchin Chiton Chiton Limpet
Rocky intertidal zone on the coast of Washingtong
Keystone species: sea urchin (strongylocentrotus) chiton (Katharina)
Limpets (saltwater snails): Acamaea pelta and A. mitra consume lots of energy, but remove them will not influence community structure.

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.
re ‘zilience

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
So will a system return to its precious states after a disturbance?
This experiment demonstrated the complex responses of community to environmental perturbations.
Resilence of ecosystem
Climate change: precipitation, add more water to a grassland in California
Biomass similar, but species richness changed
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
Four trophic level, select 1, 2 or 4 species from each level
Grow with low and high nutrient supplies.
High productivity, most producers (algae) attain high growth rate. Under low productivity, the nutrient may limit certain algae grow.
The greater resilience of more diverse communities may not reflect that species may compensate with each other, but just by change include one or more species that can maintain great growth under low nutrient conditions.
Hints: Species loss may influence stability
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)
Lecture 12:
Chapter 13:

39. Northern exposure site dominated by brown alga
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
Pertubation shift communities between alternative states:
Study by ecologists at Upenn
Orginally covered by rockweed alga (Ascophyllum nodosum)
Cleared, path size from 1, 2, 4 to 8 m2
After 5 yr, one site was dominated by another alga, another site was dominated by barnicle.

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
In 1960s, people started to debate why the “earth is green”, particularly since Hairston et al’s paper publication

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
Add predatory fish reduce zooplankton and increased phytoplankont biomass, top-down control
Zooplankton  /ˌzoʊ.əˈplæŋktən/ are heterotrophic (sometimes detritivorous) plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon (ζῴον), meaning "animal", and planktos (πλαγκτός), meaning "wanderer" or "drifter".[1]Individual zooplankton are usually too small to be seen with the naked eye, but some, such as jellyfish, are large.
Zooplankton is a categorisation spanning a range of organism sizes including small protozoans and large metazoans. It includes holoplanktonic organisms whose complete life cycle lies within the plankton, as well as meroplanktonic organisms that spend part of their lives in the plankton before graduating to either the nekton or a sessile, benthic existence. Although zooplankton are primarily transported by ambient water currents, many have locomotion, used to avoid predators (as in diel vertical migration) or to increase prey encounter rate.
Ecologically important protozoan zooplankton groups include the foraminiferans, radiolarians and dinoflagellates (the latter are often mixotrophic). Important metazoan zooplankton include cnidarians such as jellyfish and the Portuguese Man o' War; crustaceans such as copepods and krill; chaetognaths (arrow worms); molluscs such aspteropods; and chordates such as salps and juvenile fish. This wide phylogenetic range includes a similarly wide range in feeding behavior: filter feeding, predation andsymbiosis with autotrophic phytoplankton as seen in corals. Zooplankton feed on bacterioplankton, phytoplankton, other zooplankton (sometimes cannibalistically),detritus (or marine snow) and even nektonic organisms. As a result, zooplankton are primarily found in surface waters where food resources (phytoplankton or other zooplankton) are abundant.

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)
Chapter 13:

49. An example of forest zonation
Determine the boundaries is not easy
Try to lower similarity among communities
Most often, subjective, depends on the objective of study
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. One view: species distributions are plotted as a function of altitude or elevation. 4 species exhibit a continuum of species regularly replacing eath other in a sequence of A, B, C and D with increasing altitude.
Another view: species distribution is a function of distance along the altidinal gradient. As we move up the mountain, the distribution of 4 species are not continuous. A number of associations are recognized as we walk along the transect.
Two views are quite different yet consistent. Each species has acontinuous response along an environmental gradient. Yet it is the spatial distribution of that environmental variable across the landscape that determine the overlapping patterns of species distribution.
Patterns of co-occurrence for 4 plant species on a landscape along a gradient of altitude

51. Same approach can be applied to patterns of forest communities in the Great Smoky Mountain National Park.
(b) associations, support the first view, Clements’s view.
(c) Species appears to be distributed independent of each other, supporting Gleason’s view.

52. THE End

53. Keystone species
Keystone species: a species that has a disproportionate impact on the community relative to its abundance.
Remove of keystone species initiates changes in community structure and results in significant diversity loss.
Role in community: create or modify habitats, or influence interactions with others.
Lecture 12:
Chapter 13:

54. Keystone species examples
Coral (Oculina arvbuscula) in the eastern coast of US
This coral has complex branch and provide shelter of more than 300 species of invertebrates
African elephants in the savannas of southern Africa
Elephants are destruct feeders, damage trees, reduce density of shrubs, but increase grass growths.
Predator often function as keystone species
Sea otters  urchins  kelp bed (provide habitats for others)
If sea otters pop declines, urchins pop increase, overgrazing of kelp, loss of habitats for others
Wolf in Yellowstone national park: wolf  deer, - trees  birds etc.

55. Change in nutrient level can switch a marine community between alternate state
High nutrient, large diatoms grow well, Copepods swtich diet and eat large diatoms, as a result, ciliates populations increase, and their food small algae population are greatly reduced.
Low nutrient conditions favor the growth of small algae over large diatoms, so Copepods feed on ciliates, and the drop in ciliates population release the small alage from consumer pressure. So change in nutrient level can switch the system between alternative states.
Copepods suffer from predation from jellyfish, whose top-down control effects also depends on nutrient status. High nutrient, jellyfish predate on copepods reduce consumption of copepods on large diatoms. Which dominate system and produce high productivity. At low nutrient, jellyfish predation on copepods reduce consumption of ciliates, results in a reduction of small algal biomass.