BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 15: Community Lecture 15: Community StructureStructure

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Case study: Global Change

Invasive plant species, the role of herbivores and Meta-Analysis

John Parker, Georgia Tech

Question: How native and introduced herbivores affect the abundance of native and introduced plants.

Papers: 63 studiesHerbivores: bison, deer, rabbits

Wide spread of invasive species: lack of natural enemies (no predators, parasites, pathogens)

Results are not conclusive.

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.

What do the results of the meta-analysis tell us?

1.What invasive plant spp encounter matters (escape of native herbivores at home, but face new generalist herbivores that they have not evolved defense)2.Native species survive better with native herbivores (co-evo)3.Single study can’t reveal this information, as only native or invasive spp used.

BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 15: Community Lecture 15: Community StructureStructure

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Outline (Chapter 18)Outline (Chapter 18)Community structureCommunity structure

15.1 A biological community is an association of 15.1 A biological community is an association of interacting populationsinteracting populations

15.2 Measure of community structure include numbers 15.2 Measure of community structure include numbers of species and trophic levelsof species and trophic levels

15.3 Feeding relationships organize communities in 15.3 Feeding relationships organize communities in food websfood webs

15.4 Food web structure influences the stability of 15.4 Food web structure influences the stability of communitiescommunities

15.5 Communities can switch between alternative 15.5 Communities can switch between alternative stable statesstable states

15.6 Trophic levels are influenced from above by 15.6 Trophic levels are influenced from above by predation and from below by productionpredation and from below by production

15.1 A biological community is an 15.1 A biological community is an association of interacting populationsassociation of interacting populations

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

Organismic (Holistic) concept: Distribution of species is discrete (associations) Association: a type of community with 1. relative consistent species evolved together; 2. a uniform general appearance; 3. 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.

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.

Two views of community

Organismic and individualistic views

Holistic (discrete) or continuum

Ecotones

Closed or open communities

EcotonesEcotones

Ecotons are places where many species reach the edges of their distributions

Locate: sharp physical differences separate distinct associations

Differences in soil conditions may Differences in soil conditions may result in ecotonesresult in ecotones

Serpentine soil: soil with high Mg and asbestos, greenish, brownish.

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

The continuum concept and The continuum concept and gradient analysisgradient 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: precipitationEnvironmental gradients

Continuum concept.

Gradient analysis

The dominant tree species of the Great Smoky Mountains show distinct but overlapping distributions

Abundance of each species is plotted on a continuous gradient of one or more environmental factors.

Many gradient analyses have Many gradient analyses have revealed open community structurerevealed open community structure

15.2 Measures of community structure 15.2 Measures of community structure include numbers of species and trophic include numbers of species and trophic

levelslevelsBiological structure of a community is defined by the Biological structure of a community is defined by the

mix of species, including both mix of species, including both their number and their number and relative abundance.relative abundance.

Attributes of community structureAttributes of community structure1.1. Species richness: number of species that occur Species richness: number of species that occur

within the communitywithin the community2.2. Relative abundance: counting all individuals of each Relative abundance: counting all individuals of each

species in a number of sample plots within a species in a number of sample plots within a community and determining what percentage each community and determining what percentage each contributes to the total number of individual of all contributes to the total number of individual of all species.species.

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.

Tropical forests harbor the greatest species richness of any communities

AutotrophicAutotrophicHeterotrophic Heterotrophic

Primary producerPrimary producerPrimary consumersPrimary consumersSecondary Secondary

consumersconsumers

Guild: Guild: groups of groups of species that feed species that feed on similar on similar resources, have resources, have similar ways of similar ways of life.life.

(leaf eater, stem (leaf eater, stem borer, root chewer borer, root chewer etc.)etc.)

Trophic levelsTrophic levels

15.3 Feeding relationship organize 15.3 Feeding relationship organize communities in food webscommunities in food webs

Food web Food web An abstract representation of feeding An abstract representation of feeding

relationships within a community.relationships within a community.

Food chainFood chainGrass Grass grasshopper grasshopper sparrow sparrow hawk hawk

A series of arrow, each pointing one species to A series of arrow, each pointing one species to another, representing flow of food from prey another, representing flow of food from prey to predator.to predator.

Food webs describe species Food webs describe species interactionsinteractions

Food web:Food web:Involve numerical food chains meshed Involve numerical food chains meshed

together.together.Hypothetical food web:Hypothetical food web:

Circle: speciesCircle: speciesLinks:Links: arrows from one to arrows from one to anotheranotherBasal species:Basal species: feed on no feed on no others, but are fed upon by others, but are fed upon by othersothersIntermediate species: Intermediate species: feed feed on others, and are fed uponon others, and are fed uponTop predator:Top predator: not subjected not subjected to predator, but prey on other to predator, but prey on other species.species.Trophic levelsTrophic levels

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

Effects of species richness on food web structure

Intertidal mud flat Plant-insect-parasitoids7 spp 8 species7 links 12 linksOne omnivory spp 5 omnivory

Pitcher plants communities in different regions (Indian Ocean)

Increasing species richness is associated with increasing food web complexity.

Source of food:A: live insectB: dead insectC: organic debris

Species richness and food web complexity

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

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).

Recap

1.Two views of biological community (organismal and individualistic; closed and open; discrete and continuum)2.Ecotone and Gradient analysis3.Community structure (species richness and relative abundance)4.Food web and food chair and stability of community

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.

A variety of food web typesA variety of food web types

Food webs can be distinguished into different typesFood webs can be distinguished into different types

Connectedness webConnectedness web: emphasize feeding relationships : emphasize feeding relationships among species, portrayed as links in food webamong species, portrayed as links in food web

Energy flow web:Energy flow web: connections between species are connections between species are quantified by the flux of energy between a resource quantified by the flux of energy between a resource and its consumerand its consumer

Functional web:Functional web: influence on the growth rate of other influence on the growth rate of other species population.species population.

Three types of food web

Limpet Sea urchin Chiton Chiton Limpet

Case study: Indirect effect: Fox predation on seabirds transforms plant communities on a subarctic island

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

Without fox With fox

15.4 Food web structure influences 15.4 Food web structure influences the stability of communitiesthe stability of communities

Some consumers are keystone species and play an important role Some consumers are keystone species and play an important role in community structure.in community structure.

How about the food web structure on stability of communities?How about the food web structure on stability of communities?

Stability: constancy and resilienceStability: constancy and resilience

Constancy: a measure of ability of a system to resist change in Constancy: a measure of ability of a system to resist change in the face of outside influences (resistance)the face of outside influences (resistance)

Resilience: ability of system to return to some reference state Resilience: ability of system to return to some reference state after a disturbance.after a disturbance.

Resilience means that system may have internal processes that Resilience means that system may have internal processes that can compensate for disturbance-induced changes. For can compensate for disturbance-induced changes. For example, increase in birth rate can help population move back example, increase in birth rate can help population move back after a population size decreases.after a population size decreases.

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?

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. 2006High productivity, resilience differ little among low, medium and high diversity

15.6 Communities can switch 15.6 Communities can switch between alternative stable statesbetween alternative stable states

Resiliency means that a system is able to return to a “reference” Resiliency means that a system is able to return to a “reference” state following a perturbation. Sometimes, however, a system state following a perturbation. Sometimes, however, a system can have more than one stable reference state.can have more than one stable reference state.

Predation and prey: upper and lower equilibrium states of prey Predation and prey: upper and lower equilibrium states of prey populationpopulation

Stable state: small perturbations are followed by return to the Stable state: small perturbations are followed by return to the reference statereference state

Biological community might have multiple stable states:Biological community might have multiple stable states:Two keystone species respond differently to climate change:Two keystone species respond differently to climate change:Global warming may shift the community to species favors Global warming may shift the community to species favors

warming climatewarming climateRainfall Rainfall tree grow, dry->fire tree grow, dry->fire grassland community grassland community

structure. (shrubland structure. (shrubland grassland) grassland)

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

15.7 Trophic levels are influenced from 15.7 Trophic levels are influenced from above by predation and from below by above by predation and from below by

productionproduction

The Earth is Green: Hairston, Smith, Slobodkin (1960):The Earth is Green: Hairston, Smith, Slobodkin (1960): “ “carnivores depress the population of herbivores that would carnivores depress the population of herbivores that would

otherwise consume most of the vegetation”otherwise consume most of the vegetation”

Trophic cascade: When the indirect effects of consumer-resource Trophic cascade: When the indirect effects of consumer-resource interactions extend through additional trophic levels of a interactions extend through additional trophic levels of a community.community.

Top-down control: when higher trophic levels determine the size Top-down control: when higher trophic levels determine the size of trophic levels belowof trophic levels below

Bottom-up control: when the size of trophic level is determined by Bottom-up control: when the size of trophic level is determined by the rate of production of its food resourcethe rate of production of its food resource

Trophic structure of a community may be determined by bottom-up or top-down control

Cases for bottom-up, top-down control or both

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

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

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)

Another nice example to demonstrate the indirect interactions

Presence or absence of fish influence dragonfly density

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.

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

The concept of community revisitedThe 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)

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

An example of forest zonation

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

THE End

Keystone speciesKeystone species

Keystone species: a species that has a Keystone species: a species that has a disproportionate impact on the community disproportionate impact on the community relative to its abundance.relative to its abundance.

Remove of keystone species initiates changes Remove of keystone species initiates changes in community structure and results in in community structure and results in significant diversity loss.significant diversity loss.

Role in community: create or modify habitats, Role in community: create or modify habitats, or influence interactions with others.or influence interactions with others.

Keystone species examplesKeystone species examples

Coral (Oculina arvbuscula) in the eastern coast Coral (Oculina arvbuscula) in the eastern coast of USof US

This coral has complex branch and provide This coral has complex branch and provide shelter of more than 300 species of shelter of more than 300 species of invertebratesinvertebrates

African elephants in the African elephants in the savannas of southern savannas of southern AfricaAfrica Elephants are destruct Elephants are destruct feeders, damage trees, feeders, damage trees, reduce density of shrubs, reduce density of shrubs, but increase grass but increase grass growths.growths.

Change in nutrient level can switch a marine community between alternate state