Community Ecology Bio 147/247 Species Richness 3: Diversity& Abundance Deeper Meanings of Biodiversity Speci es and Functional Groups The main Qs for today are: 1. How many species are there in a community? 2. What is diversity? 3. How are the abundances of species distributed within communities? 4. Are Functional Groups: another way to think about community organization? Benefit Q1. How many species are there in a community? The lectures and readings for the last few days assumed that S was appropriately measured and standardized. But S is usually not known exactly and in most studies is only an estimate! Rarefaction Curve = Species Accumulation Curve This graph is a cost:benefit analysis that shows catch per unit effort. Cumulative S S 2 S 1 Problem 1: How much effort should we exert to get S? Is it worth the cost (effort) to get to S 2? Or is S 1 good enough, with ~ half the effort? 1 2 Effort ( Cost ) Problem 2: How can we compare studies or sites with different rarefaction curves? 1
Q2: What is diversity (in the strict, ecological sense)? Spp Comm A Comm B 1 50 90 2 50 10 Q: which community has higher diversity? Diversity Species diversity S and relative abundance. Different measures, but all treat a species as information. p i = proportion of species I in a sample. Both in Morin: Shannon-Weaver (= Shannon Weiner) Simpson s index Diversity Index H = - Σp i log e p i D = 1 _ 2 Σp i H A =.69 D A = 2 H B =.33 D B = 1.22 Evenness = Equitability J = H H max = - Σp i log e p i log e S D D max H max = H if species were equally common D max = D if species were equally common J A = J B = Types of Diversity (a scale issue): D and H = Local Diversity: Between-habitat Diversity: α diversity Point diversity Within habitat diversity Community diversity β diversity (across different communities) Regional diversity (Combines α and β): γ diversity 2
Q3. How are the abundances of species distributed within communities? 1. Distributions of abundance : Dominance-diversity curves = Rank-abundance curves Log Log-normal Veil line effect sample more of the rarer species with increased sampling effort. (see b) below. 3
2. Examples of dominance-diversity (= rank-abundance) curves in nature: a) Communities may have very different rank abundances 1. Tropical wet forest (Amazon) 2. Tropical dry deciduous forest (Costa Rica) 3. Marine copedods N. Pacific. 4. Breeding birds UK 5. Tropical bats (Panama) b). Some communities seem to get more lognormal as sample size increases (veil line effect). c) BUT: there is little theoretical reason to expect a long-normal distribution in nature. Many studies show that the distribution is skewed, with more rare species than predicted by the log-normal. 4
c) Rank abundance (dominance/diversity) patterns may also change predictably with: i) S ii) Succession Year in sequence of forest succession 5
iii) Resources Very rare spp Similar sequence for: Communities becoming polluted (e.g., higher nutrient levels [=eutrophication]) : log normal (low nutrients) geometric (high nutrients) The best references for biogeography and biodiversity: Rosenzweig, ML. 1995. Species Diversity in Space and Time. Hubbell. SP. 2001. The Unified Neutral Theory of Biodiversity and Biogeography 6
2. Functional Groups (=Guilds) Subsets of species w/in communities = another way to group species and to study communities. How to identify functional groups? a. Exclusive categories Resources Life-styles Physiology Morphology Phenology (timing) Shared predators Terrestrial Plants Mutually exclusive: N-fixers (use atm N2) C3 grasses C4 grasses Woody plants (non-fixing) herbs OR: Timing Winter annuals Summer annuals Perennials Different guilds can be based on any or all of these characteristics of species. Marine Algae Micro-algae (tiny) Foliose algae (leafy) Macro algae (kelp) Crustose algae (encrusting) Feeding Feeding methods Species used Predators: similar food all in same group Hyperparasitoids (parasitize other parasites) Parasitoids (= insect parasitizing other insects) : by species attacked Herbivores: by feeding method 7
NOTE: A given species might be grouped differently using different criteria. Is this a problem? Why? b) Statistical definitions (e.g. using classification methods). Guild (= fn group) structure of grasshopper assemblies in relation to patterns of habitat use. Guild structure is ascribed from cluster analysis of species in relation to expressed overlap in resource (= different species of plants) use (from Joern and Lawler, 1981). How these 21 grasshoppers.use resources. 8
b. Is guild membership constant? Comparing the same resource base in different regions: insects feeding on different plant parts. (i) Bracken fern- has a natural, world-wide distribution. Niche matrices defining the feeding sites and feeding methods of herbivorous arthropods on bracken in different parts of the world ( ). Feeding sites of species with >1 part of the frond are joined by lines. (Lawton) (ii) Red oak: Differences in native (England) and introduced (Canada) regions. 9
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