Counting species. Types of ecological diversity. Diversity can be partitioned geographically

Transcription

1 where are all these species (space)? Different patterns at different scales, so include both ecological and evolutionary time speciation and extinction immigration, species interactions, local extinctions Counting species Background reading for next few weeks: Purvis and Hector (2000) Getting the measure of Biodiversity 2 Types of ecological diversity Species richness (relatively) simple to measure Easily interpreted Heterogeneity Compound measure (Richness & evenness) Difficult to interpret Evenness sensitive to # spp. Diversity can be partitioned geographically!-diversity The variety of organisms in a particular place or community: thought of as a subset of some maximum. "-diversity Vague: the difference in!-diversity between or across communities OR the turnover of!-diversity as one moves from one community into another. #-diversity The total number of species (variety or organisms) in a larger region: the pool of species that alpha and beta diversity draw from. Krebs 1999

2 Species diversity indices Different metrics for different uses Lognormal Species-Area extrapolation Accumulation curves Michaelis-Menton Fisher s alpha Coleman Rarefaction Observed Spp. Bootstrap Jackknife (1-5) Chao1 Chao2 ACE (abundance-cover) ICE (incidence-cover) And many more! 1. absolute measures of richness (how many species are in this community?) vs. 2. relative measures of richness (Are there more here than there, or now than before?) General structure for absolute measures Direct Measurement (incomplete) Mathematical Extrapolation (inaccurate?) ˆ S = Observed + Missed Absolute richness Estimators Parametric Accumulation Curves Lognormal Non-Parametric Jackknife Bootstrap Chao1 & Chao2 Coverage Estimators

3 Empirical fact: most things are rare Observed Species and Sampling Effort rarity is the attribute of vast numbers of species in all classes C. Darwin, 1859 Log transform and "bin" # Species (Observed) True # Spp.? Some old data from Williams (1964) But the more we sample, the more species we get Samples (through time, or across space!) (written by an SFU graduate student!) Cannot extrapolate accumulation curves Observed richness Number of individuals , moths in Lethbridge, Alberta individuals, 291 spp, 88% 'complete' Preston,

4 So we could use this 'expected' distribution to estimate total number of species? fish per trawl 13 Magurran 2004 abundance octave I am told this is a no-no, because, like extrapolation, it is imprecise Richness Estimators Non-Parametric Estimators Parametric Assume underlying distribution of species within sample These are often wrong, or dubious Non-Parametric Jackknife Chao1 & Chao2 Coverage Estimators (Most) Developed to estimate populations of animals from mark-recapture studies with unequal capture probabilities among individuals Adapted to estimate number of species in a community, based on number of times each species occurs in samples With unequal capture probabilities among species No Assumptions about: Numerical distribution Relationship between species

5 Sexual Selection and Local Extinction - Doherty et al. PNAS 2003 Jackknife # uniques (Species in only 1 sample) # duplicates (Species in 2 samples) # m " 1% Sˆ Jack1 = Sobs + Q1 $ m & 2 # % Q (2m " 3) Q (m " 2) 1 2 Sˆ Jack 2 = Sobs + Q1 ' " ( m m(m " 1) & $ Bird Roadrunner # Observed Spp. Birders Geococcyx californiaus # Samples (quadrats)! Because the 2 classes of bird might have different detection probabilities, have to make correction to avoid bias: Just need to decide on rare threshhold estimate number seen only once # samples Use a jackknife estimator for number of species on a route = number of stops actual number seen over all stops So harder to see class gets bumped up by more species (at the limit, there is a missing species for every one only seen once!) rare spp. Rank Spp. by observations Uniques

6 Different metrics for different uses 1. absolute measures of richness (how many species are in this community?) 2. Comparing Communities most common method is rarefaction (on the board) vs. 2. relative measures of richness (Are there more here than there, or now than before?) Butterflies recovery in burned Bornean forests Bornean continuous isolated burned 23 Fewer endemic species recover from fire! Cleary & Mooers, 2006

7 Rarefaction Question: How do B vs B' abundance distributions differ? Species observed sample size not observed Number of individuals B A B folks don t like this