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OUR Ecological Footprint - 5 1. 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 in notes from movie for EC Opportunities • IB 390 Introductory Research • IB 490 Independent Study • See Website for IB Majors www.life.uiuc.edu/sib/390_490.htm Next week: • Lab • Homework 10 ANOVA • 5 Abstracts for SDP2 • Group Proposal WS - 3 days before lab • Exam 2 • Formulae will be provided. • BRING calculator. • Practice ?s: on web on Exam 2 date Ch 21: Community Structure Ch 21 +23 Community Ecology Species Abundance and Biodiversity Objectives • Species at regional vs. local scale • Species sorting ---> local composition • Species richness (# species) Local + regional components • Species relative abundance Patterns Controls • Species-area relationship • Species diversity Hypotheses to explain variation in SD Sample Exam ? • • • 1) 2) 3) 4) 5) 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. Summarize the major result of the study. What 2 components of a community does the Shannon-Wiener Index (H’) incorporate? What combination of these components yields the greatest value of H’? Explain the results in terms of competition and niche theory. Do the results support the hypothesis that the superior competitor can exist at lower resource levels than its competitors? Explain. 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 Environmental filters eliminate species that can’t tolerate conditions---> species sorting Many factors influence regional and local species richness. 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 H1:Species sorting (and beta diversity) 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 Species in communities vary in relative abundance. Most species are rare; few are common. 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 greatest evenness in abundance? Log scales… Most Least Rank order of abundance Number of species increases with area sampled. log log Species - area relationship: • S = c Az • S = # of species • A = area • c and z = fitted constants • log S = log c + z log A = linear • z (slope) = usually 0.2 to 0.35 • z = less for continental areas, greater for islands • Rapid dispersal within continental areas prevents local extinction within small areas ***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 Area and habitat diversity both contribute to the species-area relationship. Spatial variation in woody species richness Hypotheses to explain variation in species richness 1 2 3 4 5 6 Heterogeneity in space and time (Vegetation and food complexity) Predation Competition/niches Disturbance Equilibrium models 1 Heterogeneity in space and time hypothesis • Interacts with production hypothesis • Relates to niche arguments (see below) 2 Vegetation (structural complexity) overrides primary production in determining local richness. Communities with simple vegetation structure have lower richness, yet can have very different levels of productivity. Bird richness increases with greater structural complexity. Species richness increases as a stream becomes larger and has more habitat and food diversity. 3 Predation hypothesis • High productivity---> high predator populations ---> reduce competition among prey and permit more to coexist (starfish experiment) • More predation---> more selection for escape adaptations by prey Crypsis to avoid predation Pest pressure hypothesis for maintaining tree species richness Distance-dependent mortality is consistent with the pest pressure hypothesis. Soil pathogens kill seedlings near parent trees ---> maintain species richness? 4 Competition hypothesis: • High richness --> less competitive exclusion? • 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 Does increase in niche diversity --> increase in species richness? As s.r. increases, so does morphological diversity. 4 Competition hypothesis, cont.: • High richness --> less competitive exclusion? • Why? By what means? • greater specialization (narrower niche) • greater resource availability (greater niche space) • reduced resource demand (smaller populations) • intensified predation (populations below K) • Are there more ecological roles in tropics? • Greater niche space from greater number of niche axes and length of each axis? • relates to heterogeneity in space/time hypothesis Populations in regions with few species show ecological release (and larger realized niches). Less regional species ---> 1) less local sp. rich 2) each species more abundant greater habitat breadth 3) beta diversity (turnover of species) decreased. • Realized niche is always smaller than fundamental niche, • but with ecological release ---> larger realized niches 5 Intermediate Disturbance Hypothesis • Richness peaks at intermediate levels Too low disturbance --> competitive exclusion Too high disturbance --> limited number of species adapted 6 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. Nile perch vs. cichlid fish in Lake Victoria Scientific Process • Observation: Cichlid fish populations declined after the introduction of Nile perch. • Question: Did the introduction of the perch cause the decline in cichlid populations? ***Generate an ‘if…then’ hypothesis/prediction • Hypothesis 1: If introduction of Nile perch caused the decline of cichlid populations, • then • 1) lower cichlid populations in areas with high than low perch populations. 2) then higher cichlid populations in areas with perch removed than in control areas. ***What are independent and dependent variables? • Plot each prediction. • Which provides a stronger test of the hypothesis? • If get no support, what do next? ***Are there alternative hypotheses? • H1: original hypothesis • H2: A newly introduced cichlid parasite caused the decline. • H3: A marked decline in aquatic vegetation on which cichlids feed caused the decline. • H4: Dramatic changes in water chemistry caused by agricultural runoff caused the decline. • H5…. 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. Measures of community structure • 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 / pi2 p = proportion of each species in total sample • Shannon-Wiener index: H' = - pi ln pi • Evenness = ratio observed/maximum diversity ED = D/Dmax, where Dmax = S or EH’ = H'/Hmax, where Hmax = ln S Calculate Species Diversity: Species No. Ind. pi pi2 1 5 .25 .0625 2 4 .20 .0400 3 3 .15 .0225 4 4 .20 .0400 5 4 .20 .0400 Total (N) 20 1.00 ∑=.205 ln pi -1.386 -1.609 -1.897 -1.609 -1.609 pi ln pi -.3465 -.3218 -.2846 -.3218 -.3218 ∑= -1.5965 • D = 1/ ∑pi2 = 1/.205 = 4.878 • H' = -∑ pi ln pi = 1.5965 • Calculate Evenness: • ED = D/Dmax 4.878/5 = .9756 • H' = H'/Hmax = 1.5965/1.609 = .9922 (Dmax = S) (Hmax = ln S) Comparisons of diversity indices among communities. C1 C2 C3 C4 C5 •***What factors increase species diversity? • more species. • less difference in relative abundance among species. Objectives • Species at regional vs. local scale • Species sorting ---> local composition • Species richness (# species) Local + regional components • Species relative abundance Patterns Controls • Species-area relationship • Species diversity Hypotheses to explain variation in SD Measures to quantify and compare SD