OUR Ecological Footprint …

Fall 2008 IB Workshop Series sponsored by IB academic advisors Study Abroad for IB Majors Thursday, October 30 4:00-5:00PM 135 Burrill Hall Learn about Study Abroad opportunities of special interest to IB students.

Ch 21,23,24 Community Ecology Species Abundance + Diversity

Objectives Species relative abundance Species diversity Measures to quantify and compare SD Local SD affected by Biotic Interactions Disturbance Species-area relationship

Species in communities vary in relative abundance. Are most species are rare or common? Figure 1

What is the likelihood of sampling a rare species? A common species? How accurate are the data for rare species?

Species abundance (dominance diversity) curves…Which community has 1) ? 2) ? Log scale… Rank order of abundance MostLeast Figure 2

How can community structure be quantified and compared?

*** Which variables can be used to describe the species diversity of a local community? Which community is more diverse? Species richness Species relative abundance Figure 3

Species richness: # of species BUT species differ in abundance and thus in role Species diversity: weight species by their relative abundance 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 ∑= H' = -∑ p i ln p i =

Comparisons of diversity indices among communities. Which community is most diverse? What factors increase species diversity? more species. less difference in relative abundance among species. C1 C2 C3 C4 C5 Figure 4

Multiple scales of species diversity Local Regional Latitudinal Continental Global

Factors Affecting SD at Local Scale: Abiotic factors Biological interactions Dispersal limitation Human introduction Chance

QUESTION: Abiotic factors + Diversity A 100-yr experiment tested the effect of fertilizer on species diversity (H’) in a grassland. RESULTS: H’ of unfertilized remained steady. H’ of fertilized decreases through time. 1)Summarize the major result of the study. 2)What 2 components of a community does the Shannon-Wiener Index (H’) incorporate? 3)What combination of these components yields the greatest value of H’? 4)Explain the results in terms of competition and niche theory. Figure 5.

Biotic Hypotheses to explain variation in species richness 1 Heterogeneity in space and time e.g. (Vegetation and food complexity) 2 Herbivore and pathogen pressure 3 Competition/niches 4 Disturbance 5 Equilibrium models

1 Heterogeneity in space and time hypothesis Relates to niche arguments (see below)

Bird richness increases with greater structural complexity.

Species richness increases as a stream becomes larger and has more habitat and food diversity.

2) Pest pressure (herbivores + pathogens) hypothesis for maintaining tree species richness Figure 6.

Distance-dependent (and/or density- dependent) mortality is consistent with the pest pressure hypothesis. Figure 7

3 Competition hypothesis: High richness --> less competitive exclusion?--> more species Why? By what means?

Niche metrics

How can more species be added to a community? Increase total niche space Increase niche overlap Decrease niche breadth Figure 8

4 Competition hypothesis, cont.: High richness --> less competitive exclusion? Why? By what means? greater specialization (narrower niche) greater resource availability (greater niche space); less niche overlap reduced resource demand (smaller populations) Greater niche space from greater number of niche axes and length of each axis? relates to hypothesis of heterogeneity in space/time

Does increase in niche diversity --> increase in species richness? As s.r. increases, so does morphological diversity.

Populations in regions with few species show ecological release (and larger realized niches).

Realized niche is always smaller than fundamental niche, but with ecological release ---> larger realized niches

4 Intermediate Disturbance Hypothesis Richness peaks at intermediate levels Too low disturbance --> competitive exclusion Too high disturbance --> limited number of species adapted

5 Equilibrium hypothesis Richness reaches an equilibrium when factors removing species = factors adding species.  more additions (e.g. speciation) or and/or fewer deletions (e.g. extinctions) = greater species richness.

Multiple scales of species diversity Local Local Affected by Regional Regional Latitudinal Continental Global

Local diversity as f (regional diversity). Figure 9

Many factors influence regional and local species richness. Figure 10

Local communities contain a subset of the regional species pool. ***What determines whether a species can be a member of a given community? 1 Adaptations of species to environmental conditions (habitat selection) 2 Persistence in face of competitors, predators, and parasites

Local communities are assembled from the regional species pool. Species sorting = processes that determine local community composition.

Experimentally-composed communities show species sorting. What caused the sorting? Fertility: low high Regional: # species available Local: realized #

Environmental filters eliminate species that can’t tolerate conditions---> species sorting

H 1 :Species sorting should be greatest where regional species pool is largest. When species pool is smaller, competition should be relaxed---> ecological release = species expand into habitats normally filled by other species and increase in population density Ecological release provides evidence for hypothesis of local interactions controlling species diversity. (e.g. competition for resources structures communities and limits # species)

Species richness (# species) has both local and regional components.  (alpha) = local # species in small area of homogeneous habitat  (beta) = # species turnover between habitats  (gamma) = (landscape) regional: total # species in all habitats within a barrier-free geographic area

Above species richness measures determined by ecology and regional pool  (delta) = available pool of species within dispersal distance (up to continental scale) determined evolutionarily

What is the relationship between species # and area? What scales are used? log Figure 11

Species - area relationship: S = c A z S = # of species A = area c and z = fitted constants log S = log c + z log A = linear

***Why do larger areas have more species? in part because… larger areas give larger samples but also… greater habitat heterogeneity (sample more types of habitats) larger islands---> bigger target for immigrants larger populations ---> –greater genetic diversity –broader distributions over habitats –numbers large enough to prevent stochastic extinction

What contributes to these species-area relationships?. Figure 12

OBJECTIVES Species Diversity at larger scales Equilibrium theory + Island Biog. Theory Regional effects on local SD Regional SD Latitudinal SD Continental/Global SD