OUR Ecological Footprint Recycle; pay tax for it. 2. Live near work; Ride bike; minimize car use. 3. Buy energy-efficient furnace. 4. Programmable thermostat: winter/summer 5. Turn off lights when leave room; unplug appliance 6.

Next week’s Lab: Data Analysis in Computer Lab Data Entry to Excel: Each individual MUST enter all data before lab SDP2 Manuscript 1 draft ONLY Introduction Methods Literature Cited

Ch 23: Community Development

Ch 21: Community Structure

Objectives How are communities measured/compared? Is the community a natural unit? Are communities in equilibrium? stable? How strong are connections among species? How are food febs measrued/compared? Do complex food webs aid stability? What controls abundance within trophic levels? Do keystone species aid stability? Next lecture: How do communities change following disturbance?

What is a community? assemblage of species that co-occur in the same place.

What is a community here? How many are there?

How many are here? How abrupt are boundaries of these communities?

How can community structure be quantified and compared?

*** Which variables can be used to describe the species diversity of a community? Which community is more diverse? Species richness Species relative abundance

Species richness (# of species) = S S varies with sample size so… Compare S by rarefaction: equal-sized subsamples randomly drawn.

Species richness: # of species BUT species differ in abundance and thus in role Species diversity: weight species by their relative abundance Simpson’s index: D = 1 /  p i 2 p = proportion of each species in total sample Shannon-Wiener index: H' = -  p i ln p i Measures of community structure

Calculate Species Diversity: Species No. Ind. p i p i 2 ln p i p i ln p i Total (N) ∑=.205 ∑= D = 1/ ∑p i 2 = 1/.205 = H' = -∑ p i ln p i =

Comparisons of diversity indices among communities. ***What factors increase species diversity? more species. less difference in relative abundance among species. C1 C2 C3 C4 C5

‘Community’ has many meanings: Spatially defined Functionally defined --> focus on interactions Community = an association of interacting populations First: focus on spatially defined…

Is the community a natural unit of ecological organization? Closed vs. open community structure… Holistic Individualistic

Soil conditions reflecting underlying geology may cause prominent community boundaries = ecotone.

Concentrations of soil minerals change sharply across ecotone.

Replacement of species across an ecotone.

Historical arguments… What is the ‘nature’ of the community? Clements: holistic concept superorganism/interdependent whole greater than sum of parts closed with discrete boundaries emphasis descriptive and on classification

Gleason (UI!): individualistic concept haphazard assemblages of species not interdependent open with no natural boundaries emphasis on community dynamics and functional organization Which concept has most support?

Whittaker (UI!): gradient analysis How are species distributed along a physical gradient? Open or closed? Ecotones? Continuum? Most communities are open… species distribute independently of other species.

Continuum concept: Within broadly defined habitats, species replace one another continuously along gradients of physical conditions.

***Do these data support the ‘continuum concept”?

***Do these data support a stable (equilbrium) or transient (non-equilbrium) view of the community?

Question: Do identical communities develop in identical environments? ‘Clemensian’ hypothesis: yes ‘Gleasonian’ hypothesis: no Experimental set-up? ‘Clemensian’ prediction: Identical plankton communities will develop in all ponds. ‘Gleasonian’ prediction: Different plankton communnities will develop in different ponds.

2.Examine water samples; 3. ID each speciesPresent in each pond.

What is conclusion?

What is the ‘nature’ of the community? How tightly connected are species? Are communities stable or transient? Later models Redundancy Rivet Non-equilibrium Equilibrium OPENCLOSED

How can community structure be quantified and compared?

*** Which variables can be used to describe the species diversity of a community? Which community is more diverse? Species richness Species relative abundance

Species richness (# of species) = S S varies with sample size so… Compare S by rarefaction: equal-sized subsamples randomly drawn.

Species richness: # of species BUT species differ in abundance and thus in role Species diversity: weight species by their relative abundance Simpson’s index: D = 1 /  p i 2 p = proportion of each species in total sample Shannon-Wiener index: H' = -  p i ln p i Measures of community structure

Calculate Species Diversity: Species No. Ind. p i p i 2 ln p i p i ln p i Total (N) ∑=.205 ∑= D = 1/ ∑p i 2 = 1/.205 = H' = -∑ p i ln p i =

Comparisons of diversity indices among communities. ***What factors increase species diversity? more species. less difference in relative abundance among species. C1 C2 C3 C4 C5

Community: functionally defined

How strong are the connections among species in a community? Rivet model tight linkage in ‘web of life’ obligate associations of species or obligate exclusion of species Redundancy model loose ‘web of life’ most species have no impact on other species species and ecological processes are redundant

***What are conservation implications of the two contrasting models? Would focus be on community dynamics or single-species dynamics? In which model are keystone species important?

Feeding relationships organize communities in food webs. Communities of similar diversity can have very different food webs.

***What changes with increased food web complexity? What doesn’t change? # trophic levels 3 4 6

Variables that quantify food webs: # species # guilds (groups of species with different feeding or foraging ecology) Total # feeding links # feeding links per species Connectance = # interactions/total possible = # interactions/[S(S-1)/2] Linkage density = # interactions/# species

Does greater complexity of food web increase community stability?

***Does food web complexity lead to increased community stability? Pro: alternative resources--->less dependent on fluctuations in any one resource energy can take many routes --> disruption of one pathway shunts more energy to another Con: more links may create pervasive, destabilizing time lags in population processes

Question: Which are more stable when disturbed: species-rich or less-diverse communities? Hypothesis: Resistance to disturbance increases with increasing species richness. Null hypothesis: No relationship exists between resistance and species richness. Experimental Design? Prediciton: Plots with more species before drought are more resistant to change. Null prediction: All plots have similar resistance regardless of species richness.

What is the conclusion?

Different approaches to depict food webs---> show different ways in which populations influence one another. Connectedness Energy flow Functional

What influences abundance with each trophic levels? H 1 : predation (top-down control) H 2 : production by plants (bottom-up control). Trophic cascade links all trophic levels. Bottom-up Top-down

Trophic cascade: indirect effects of consumer-resource interactions extended through additional trophic levels of the community. top-down effect consumers depress size of trophic level immediately below them, which indirectly increases populations two tropic levels below.

Keystone species: non-redundant, key species in maintaining community stability and diversity can be: plants herbivore top predator

If a beetle is the keystone species, then…removal of the beetle will ---> lower species diversity.

Objectives How are communities measured/compared? Is the community a natural unit? Are communities in equilibrium? stable? How strong are connections among species? How are food webs measrued/compared? Do complex food webs aid stability? What controls abundance within trophic levels? Do keystone species aid stability? Next lecture: How do communities change following disturbance?

Vocabulary