Species richness The number of species is an important biological variable that scientists try to quantify

Species diversity The number of species weighted by their abundance. For example, a forest with 10 tree species, each with ten individuals, is generally considered more diverse than a forest with 10 tree species, one of which is represented by 91 individuals with the other 9 species only represented by one individual each.

To estimate species richness one must first sample an area(s)

Sampling is measuring a small part of an entity assuming that this small part is representative of the larger entity

Ways to diminish biases in sampling Use multiple sampling techniques Sample at random locations (each location has an equal opportunity of being sampled--in other words, sampling should not be biased in favor of some locations and against other locations) Sample repeatedly

In addition to sampling correctly, it is important to recognize that not all species are equally detectable

In addition, species may vary in their detectability across habitat types

Generally, the number of species detected (observed) through sampling, is not the best estimate of the species richness of an area

Ways to look at patterns and estimate diversity after sampling is completed Diversity indices Accumulation curves/Rarefaction curves Using species abundance distribution data

Shannon Diversity Index Also known as the Shannon-Wiener or Shannon- Weaver. This index uses species abundances to calculate an index of diversity H = -Σ pi ln(pi) pi= proportion of the ith species

Imagine the following are the abundances of individuals in a community of frogs detected by a biologist Species 1 = 15 Species 2 = 10 Species 3 = 3 Species 4 = 1

H = -Σ pi ln(pi) = number of individuals in the community p1 = 15/29, p2 = 10/29, p3=3/29, p4=1/29 H = -Σ (0.52(ln0.52)+(0.34(ln0.34)+(0.10(ln0.10) (ln0.03) = = diversity index, which we compare to other, similarly calculated diversity indices if we want to compare the diversities of different communities

Assumption of Shannon Index All species are equally detectable This assumption may be more true for some taxonomic groups than others. In general, for mobile organisms, the Shannon Index is not a strong way to estimate diversity

Accumulation curve—”records the total number of species revealed, during the process of data collection, as additional individuals (or sample units) are added to the pool of all previously observed or collected individuals or samples” Gotelli, N.J. and R. K. Colwell Ecology Letters 4:

Braulio Carillo

Tabanid fly

Tabanid fly species accumulation curves for La Selva and 1070 m in Braulio Carillo A Report on the Tabanidae of La Selva Biological Station and 1070m in Braulio Carrillo National Park Taxonomic Collaborator: John F. Burger, Department of Zoology, Spaulding Hall University of New Hampshire, Durham, New Hampshire USA. Page author: John T. Longino, The Evergreen State College, Olympia WA USA

Accumulation curves show differences in species richness, given the number of individuals detected When these curves reach an asymptote, sampling may be reasonably complete

Rarefaction curves are produced by “repeatedly re-sampling the pool of N individuals or N samples, at random, plotting the average number of species represented by 1, 2,…N individuals or samples. Sampling is generally done without replacement”

Rarefaction curves represent the statistical expectation for the corresponding accumulation curve

Black line is accumulation curve, red line is rarefaction curve, dashed lines are confidence Intervals. Rarefaction curve is based on 100 samples. Data are for bats at site in Malaysia.

Williams et al Variation in native bee faunas and its implications for detecting community change. Ecology and Society 5:7

If one bases rarefaction curves on numbers of samples versus individuals, one needs to be careful If the density of individuals differs among samples, results will be misleading

From Gotelli and Colwell Second growth forest is denser, greater no. of individuals, so rarefying with samples gives mis- leading result that second growth forest is more species-rich. Rarefying with individuals controls for density differences. Because each sample from second growth forest has more individuals than each sample from old growth forest, the samples for the two types of forest are not directly comparable.

Another technique for comparing species richness Use program Specrich, available at pwrc.usgs.gov/software/specrich.html Patuxent Wildlife Research Center website

Community ACommunity B No of spp. detected with one individual6030 No of spp. detected with two individuals2520 No of spp. detected with three individuals1020 No of spp. detected with four individuals215 No of spp. detected with five individuals315 Which community do you think has a greater species richness?

Species abundance distribution data (as presented in the previous slide) are used to estimate species richness in this method.

Estimated species richness (interpolated N) Standard error of estimate Range of estimate Community A Community B

Characteristics of particular taxonomic or ecological groups that are more likely to be more species-rich than others? Characteristics of particular environments that are more likely to be more species-rich than others?

ControlIslandPlantation Planting design-- In islands or plantations?

San Gabriel, April 2007

San Gabriel March 2006

Loma Linda March 2006