chapter 17 community structure a community has attributes that differ from those of its components...
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Chapter 17 Community Structure
• A community has attributes that differ from those of its components– Number of species– Relative abundance of species– Nature of species interactions– Physical structure
17.1 The Number of Species and Their Relative Abundance Define Diversity
• Species richness (S) is the count of the number of species occurring within the community
• Relative abundance represents the percentage each species contributes to the total number of individuals of all species
Species Rank - Abundance Curves
Barlow J et al. PNAS 2007;104:18555-18560
primary forest
secondary forest
plantation forest
Species Accumulation Curves
17.1 The Number of Species and Their Relative Abundance Define Diversity
• Diversity indexes provide a way to quantify the relationship between species number and relative abundance
• Simpson's index (D) = (ni/N)2
= summation for all species
– ni = number of individuals of species i
– N = total number of individuals of all species– D ranges between 0 and 1 and as both
species' richness and evenness increase, the value approaches 0
17.1 The Number of Species and Their Relative Abundance Define Diversity
• Simpson's index (D) = (ni/N)2
• Simpson's reciprocal index or Simpson's diversity index = 1/D– The lowest possible value is 1, representing a
community containing only one species– The maximum value is the number of species
in the community (species richness: S)– Maximum value with perfect even-ness of
relative abundance
17.1 The Number of Species and Their Relative Abundance Define Diversity
• Shannon (or Shannon-Weiner) index = H = -(pi)(loge pi)
– Relative abundance of each species =
pi = ni / N
– pi = proportion of species i
• In the absence of diversity, where only one species is present, H = 0
• Hmax = ln S, occurs when all species are present in equal numbers
Species abundance (or biomass)
Species Ecological Effect
RARE
KEYSTONE DOMINANT
UMBRELLA
INDICATOR
Not all species within a community are equivalent
OTTER RECOLONIZATION
Kelp recovery in some cases
But not in others (hysteresis)
17.9 Two Contrasting Views of the Community
• Clements: Organismal concept of community organization and structure: communities are sets of species that are co-adapted to biotic interactions with one another
• Gleason: Individual concept of community organization and structure: each species largely responds to environmental gradients independently
Clements
Gleason
Ecotones ARE easily recognizable breaks in community structure, but often arise from abiotic factors, rather than biotic interactions among species
© 2012 Pearson Education, Inc.
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