Paper : 12 Principles of Ecology

Module : 18 Community: Community characteristics, types of biodiversity, diversity

index, abundance, species richness, vertical and horizontal stratification: Part II

Development Team

Principal Investigator: Prof. Neeta Sehgal

Department of Zoology, University of Delhi

Co-Principal Investigator: Prof. D.K. Singh

Department of Zoology, University of Delhi

Paper Coordinator: Prof. D.K. Singh

Department of Zoology, University of Delhi

Content Writer: Dr. Haren Ram Chiary and Dr. Kapinder

Kirori Mal College, University of Delhi

Content Reviewer: Prof. K.S. Rao

Department of Botany, University of Delhi

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 Description of Module

Subject Name ZOOLOGY

Paper Name Zool 12, Principles of Ecology

Module Name/Title Community

Module Id M18, Community characteristics, types of biodiversity, diversity index,

abundance, species richness, vertical and horizontal stratification: Part-
II
Keywords Biodiversity, Species diversity, genetic diversity, community/Ecosystem
diversity, alpha-, beta- and gamma diversity, biogeography

Contents

1. Learning Objectives
2. Introduction to Biodiversity
3. Types of Biodiversity
a) Species Diversity
b) Genetic Diversity
c) Community or Ecosystem Diversity
(i) Alpha Diversity
(ii) Beta Diversity
(iii) Gamma Diversity
4. Evolution of Biodiversity
5. Factors that Promotes High Diversity
6. Biogeography
7. Measurement of Biodiversity
8. Summary

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 1. Learning Outcomes

After studying this module, you shall be able to

• Understand the meaning of Biodiversity

• Briefly study the types of biodiversity
• Learn about the different types of community or ecosystem diversity
• Evaluate how biodiversity has evolved and the factors affecting biodiversity
• Understand the theory of biogeography

2. Introduction

As per CBD (Conventional on Biological Diversity (1992)), living organisms from all the
sources show variability among themselves called as Biological diversity. The sources of
living organisms can be marine, terrestrial or aquatic ecosystem and the ecological complexes
in which they have participated such as diversity between species, within species and of
ecosystem. The biodiversity not only include plant and animals and other living organisms
(species) but also the variety of ecosystem they inhabiat and their varied genes.

The species richness accounting for the total number of species in a community is called as
biodiversity. The numbers of species differ in different ecological communities and provide
an active area for the current research. The animal and plant life are more varied and
abundant in the tropic regions than other part of the world, stated by Alfred Wallace (1878).
MacArthur and Wilson (1967) suggested that islands exhibit different patterns of variation;
more species in large and nearer continents than remote and small islands. Conservation
biology involves the measurement of biodiversity as its important integral part. To detect and
understand the cause of formation of large patterns in groups of species, a community based
approach is employed.

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 In 1988, Norman Myers, a British biologist coined the term Biodiversity Hotspot. It is an
irreplaceable biogeographic area that is threatened with destruction and act as a significant
reservoir of biodiversity. The area must be threatened to a limit of at least 30 percent of its
original vegetation must be lost or must be irreplaceable due to the presence of high endemic
species. Around the world, there are specifically 35 areas that are biologically rich and have
lost nearly 70% of their original habitat.

The biosphere provides life support system to all living organisms and the presence of
biological diversity (innumerable organism) makes the complex life pleasant. In 1985, Walter
and Rosen coined the term biodiversity as an abbreviated form of Biological Diversity. It
took more than four billion years to originate life on earth and almost one billion year to
develop this complex and wide spectrum of life. In 1988, Wilson believed that almost 10 to
80 million of total number of species are present on earth, out of which only 1.4 million is
known to us. However, we are losing the diversity in life forms that can result into grave
consequences. The total varieties of species on earth i.e. different types of plants, animals and
microbes constitute the Biodiversity. The variety can be in any of the life forms,
combinations and levels. The Biological diversity encompasses diversity within species
termed as species diversity, genetic diversity (between species) and ecosystem diversity.

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 Figure 1. Biodiversity Pie Chart

3. Types of Biodiversity

The biological diversity is broadly categorized into three different levels —Species diversity,
Genetic diversity and Community or Ecosystem diversity.

(i) Species Diversity:

Species are a group of similar organisms that share a common lineage, interbreed and
produce offspring and called as basic unit of classification. Species diversity is commonly
used as a synonym for Biodiversity. The species diversity has evolved attributing to the
diversity in habitat of living organisms and defined as variety of species within a habitat.
Thus, based on the number of species within an area the diversity of that region can be
measured. In a given area, the species diversity is comprised of the total number of plant and
animal species in that area. Although some regions are have fewer species than others but
both type of ecosystems, agricultural and natural, have diversity. Moreover, agricultural
ecosystem has fewer varieties in species than the undisturbed natural system such as tropical
forests showing higher species richness (number of species in given habitat). Hotspots are
the areas rich in species diversity. India is among the 15 nations of the world encompassing
exceptionally rich in species diversity. The total number of species belonging to different
taxonomic groups is measured as Global Diversity.

Species diversity is studied at different levels: alpha, beta, gamma, delta and omega species
diversity. The number of species habituating at the same region is the measure of alpha
diversity. The difference in species between patches is defined as beta diversity. The
number of different species in different geographical locations is called gamma diversity.
The diversity in species of biomes is measured as delta diversity. Biomes also referred to as
ecosystem, are geographically and climatically defined ecological regions. The number of
species measured for the entire biosphere is called omega diversity. In a given area, the

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 measurement of variety of taxa (at the genus and family taxonomical levels) is referred to as
taxon or taxic diversity, that when studied at species level called as species diversity.

(ii) Genetic Diversity:

Every single organism obtains special characteristics encoded by the broad range of possible
combinations in the genes. Thus, every individual of plant or animal species vary from each
other in their genetic makeup. Even a slight variation in the genetic makeup provides
differences within a species where each individual slightly differ from each other
representing different strains, forms (variation in single morphological characteristic),
varieties and subspecies. This diversity within the species or different species due to different
genetic make-up is called as genetic diversity. Large number of strains and varieties within a
species is considered as diverse and rich in genetic organization. Chromosomal or gene
mutations cause the genetic variations in single individuals of a species. These genetic
variations are an important aspect and an integral part of biodiversity and considered as
prerequisite for adaptation and evolution. Genetic variations are studied at population level
and expressed in terms of alleles. PCR (polymerase chain reaction), DNA fingerprinting,
allozyme analysis, DNA sequencing and restriction site mapping are the currently employed
different techniques used to measure the Genetic variations.

(iii) Ecosystem or Community Diversity:

On earth large variety of different ecosystems, based on the differences in the habitat, have
their own complement of distinctive inter linked species. India is an outstandingly prosperous
in ecosystem diversity. Distinctive natural ecosystems include aquatic ecosystems like the
sea, lakes, and rivers and as well as landscapes like mountains forests, deserts, grasslands etc.
Different land-forms may exist in ecosystem, each of which supports specific and different
vegetation. Natural ecosystems become degraded and less productive when misused or
overused. Various sub-ecosystems are constituted and separated by the boundaries of the
communities that are not distinct and thus, the ecosystem diversity is difficult to measure in
comparison to species and genetic diversity. Within the given ecosystem, communities are
studied in various ecological niches to measure the ecosystem diversity. Each community has
definite complexes which are associated with structure and composition of the biodiversity.
6

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 The loss of species and genetic diversity are the ultimately caused by the loss of ecosystem
diversity. The ecosystem diversity is often called as Community diversity. The diversity of
ecological units or community types within different and large ecological niches is called as
community diversity. Community diversity is different than habitat variety that defines
different animal species living in different habitats. The number of species does not directly
affect the ecosystem processes rather significantly effect through functional differences
between species. The ecosystems with various functional traits (functional diversity) provide
high productivity, resistance and resilience to invaders and are better operated. In 1998,
Hooper suggested that the extent of functional differences within the species pool should be
studied to better understand the functional diversity. In ecological systems, different
organisms perform a range of functions summarized as functional diversity. Within the
community or habitat, the species can be divided into functionally similar taxonomic entities
like deposit feeders, suspension feeders etc or into distinct functional types like plant growth
forms, feeding guilds. These functionally similar species within the habitat can be from
different taxonomic entities.

Ecological or Community diversity has three different levels:

a. Alpha Diversity (within-habitat diversity)
Alpha diversity (α-diversity) is expressed in terms species richness or number of species in an
ecosystem. It defines the biological diversity within an ecosystem, community or simply in a
particular habitat. The alpha diversity can be measured by counting the distinct group of
organisms such as different species, genera, and families or number of taxonomic entities
(number of taxa) within the ecosystem.

b. Beta Diversity (between habitat diversity along environment gradient)

Beta diversity (β-diversity) is defined as the quantitative measurement of diversity of
communities along environmental gradients. The species diversity that experience changing
environment between ecosystems is compared to measure the beta diversity. It is given as the
rate of change in species composition among communities or across different ecological
habitat.

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 c. Gamma Diversity
Gamma diversity (γ-diversity) is defined as the species richness or total number of species
over a large region (ecological, units). Gamma diversity also called as large-scale landscape
diversity, within a region is given by the quantitative measurement of overall diversity for
different ecosystems. It is often expressed as the species richness of component communities.

Figure: 2 Three perspectives of community biodiversity

4. Evolution of Biodiversity

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 Certain ecological and evolutionary process creates the biological diversity. Ecology provides
explanations for the occurrence of enormous diversity in the biological system and the
patterns of biodiversity of existing ecosystems. Ecological processes interact with the genetic
diversity through speciation, microevolution and adaptation and result into evolutionary
consequences. The environment exerts continual pressure to diversify the life through
innovation, adaptation and exploitation of new traditions. The most prominent consequence
of ecological and environmental processes (causing species multiplication) is the species
diversity. The ecological factors that effects it includes the environmental gradients, age of
the ecosystem, architecture of the habitat, isolation, species interaction, nature of physical
environment, migration and dispersal and natural disturbances.

In 1859, Darwin projected “survival of the fittest” that species compete for the survival and
the only the fittest species will survive in nature. It was interpreted that under natural
selection pressure the species which are fit and can compete survives whereas weak and less
fit organisms gets eliminated from the nature. In 1960, Hardin was inspired by his concept
and proposed “competitive exclusion principle” which is interpreted as an idea where no
two species can coexist in the same habitat; the more competitive species causes the
exclusion of less fit species. This is the irony of biodiversity where we expect few species but
find many in nature.

5. Factors affecting Biodiversity

In 1994, Huston suggested that the biological diversity varies over both small and large
distances and from one region to other. There are certain factors that can influence these
variations in the biological diversity such as environmental factors, disturbances,
environment heterogeneity etc.
(i) Disturbance
The local species diversity is maintained by the small (minor) disturbances. Fires and
felling of the trees are the forest associated disturbances that can affect the successive

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 composition of the species. In the grasslands the increase in diversity can be offered by
the grazing animals which are considered as disturbance creating factor. These
disturbances augment biodiversity as a response consequence. In 1979, Connell
suggested that the forest at different succession levels represent combination of small
patches and subsequent disturbances contribute to diversity and provide niche. He
concluded that these disturbances initiate biodiversity.
(ii) Favourable Environmental Conditions
Under favourable environmental conditions such as growth conditions, greater diversity
is offered by the plants and animals species. But this concept is not universally
accepted. In 1991, Curriae studied the number of species of mammals, reptiles, birds,
amphibians and plants (trees) in relation to environmental situations in two different
countries (Canada and USA) and suggested that there is positive correlation between
species richness and solar influx and temperature. Thus, under these two favorable
conditions the biodiversity increases. However, many ecologists proposed different
concepts suggesting that there is no universally accepted relationship between
prevailing favorable conditions and species diversity.

(iii) Heterogeneity of the Environment

In 2000, Newman suggested that heterogeneity of the environment does not affect
alpha-diversity (α-diversity) of the community rather increases the beta diversity (β-
diversity). Within a community differences in exposure, soil depth, steepness, rock
type, wetness and other factors affecting soil properties and microclimate can cause
mosaics of varying vegetation and scale patches within a large community. The
proportion of species changes on exposure to different environmental factors as each
species responds in different manner.

(iv) Plant Species Diversity may Promote Insect Diversity

Insect diversity can be promoted by the high plant diversity. In 1993, Harborne
explained it by considering the primary cause of this diversity relationship as the
coevolution between insects and plants involving secondary metabolites or chemicals.
Flavanoids, terpenoids and alkaloids are the plant produced secondary metabolites or

10

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 chemicals which are poisonous to most animal species. However, some insect species
are tolerant to these secondary chemicals synthesized by the plants. These resistant or
tolerant insect then become specialized in consuming those plant species which produce
secondary chemicals to which these insects are resistant. Thus, only one or few plant
species are consumed by many insects. Herbivores are less confined to specific plant
species although may have preferences between different plant species. Thus, diversity
in insect species is promoted by the diversity in plant species, not necessarily for other
animals.
(v) Reducing Soil Fertility
In 2000, Newman suggested a negative relationship indicating that soil fertility
inversely affects the diversity. In the grasslands, high species diversity can be achieved
by reducing the soil fertility. The high productive grasslands show less diversity due to
intense competition between species for light. The species growing tall exclude the low
growing species when they compete for light.

6. Biogeographic aspects of diversity

In a given area, the study of species distribution is called as Biogeography. In order to

identify and observe the possible factors that can significantly affect the species diversity,
islands are the preferable choice as they provide controlled area for the observation. On an
island the rate of colonization is determined by three variables which includes the number of
species occupying the surrounding islands, the distance between the mainland and the islands
to be studied or other islands, and size of the island. Based on these variables, ecologists
proposed the “theory of island biogeography” that predict the number of species inhabiting
that island. Thus, this theory is used to give explanation for the species diversity on land like
lakes, mountaintops and forest fragments. Assuming that the extinction rate and immigration
are equivalent, this theory states that the number of species inhabiting the island is inversely
proportional to the distance between mainland and given island and directly proportional to
the size of the island.

7. Measures of Biodiversity
11

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 There are different ways to measure the biodiversity. Several metrics can be used to measure
biodiversity such as number of species or species richness; measurement of extent of
uniform/even distribution among species termed as species evenness; measurement of
variation in the genetic make-up of organisms within a population or a community called as
genetic diversity; can measure the organisms characteristics or phenotypic differences within
the community called as phenotypic variance, and measurement of the number of particular
species within the genetically different populations called as population number.
Species richness and evenness are the two main factors accounting for measuring diversity. In
the given area, the number of different species represents the species richness. Nevertheless,
richness is not the only factor affecting the diversity rather depends on evenness also. Each of
the species constitutes a different population and the similarity in the size of these
populations is compared by the evenness. Thus, evenness measure the relative abundance of
species which in turn makeup the richness of the habitat.
For instance, let’s suppose 100 individuals of each species 1 and 2 belong to two different
communities A and B, as shown in the table below:
Table: 1 Two communities composed of species 1 and 2.

Community A and B share equal species richness as the total number of individuals are 100
in each community. However, the evenness in community B is greater than community A as
the species are more uniformly distributed in community B (50:50). Thus, equal species
richness but greater evenness provides more diversity in community B than community A.
An increase in evenness and richness of species increases the diversity.

8. Summary

12

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 Living organisms from all the sources show variability among themselves called as
Biological diversity. The sources of living organisms can be marine, terrestrial or aquatic
ecosystem and the ecological complexes in which they have participated such as diversity
between species, within species and of ecosystem. The species richness accounting for the
total number of species in a community is called as biodiversity. The Biological diversity
encompasses diversity within species termed as species diversity, genetic diversity (between
species) and ecosystem diversity. Biodiversity Hotspot is an irreplaceable biogeographic area
that is threatened with destruction and act as a significant reservoir of biodiversity. The
biological diversity is broadly categorized into three different levels —Species diversity,
Genetic diversity and Community or Ecosystem diversity. The species diversity has evolved
attributing the diversity in habitat of living organisms and defined as variety of species within
a habitat. The total number of species belonging to different taxonomic groups is measured as
Global Diversity. The difference in species between patches is defined as beta diversity. The
number of different species in different geographical locations is called gamma diversity. The
diversity in species of biomes is measured as delta diversity. Biomes also referred to as
ecosystem, are geographically and climatically defined ecological regions. The number of
species measured for the entire biosphere is called omega diversity. In a given area, the
measurement of variety of taxa (at the genus and family taxonomical levels) is referred to as
taxon or taxic diversity, that when studied at species level called as species diversity. Large
number of strains and varieties within a species is considered as diverse and rich in genetic
organization. The diversity within the species or different species due to different genetic
make-up is called as genetic diversity. Chromosomal or gene mutations cause the genetic
variations in single individuals of a species. Each community has definite complexes which
are associated with structure and composition of the biodiversity. Within the given
ecosystem, communities are studied in various ecological niches to measure the ecosystem
diversity. The ecosystem diversity is often called as Community diversity. The diversity of
ecological units or community types within different and large ecological niches is called as
community diversity. The ecosystems with various functional traits (functional diversity)
provide high productivity, resistance and resilience to invaders and are better operated. In
ecological systems, different organisms perform a range of functions summarized as
13

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II
 functional diversity. Ecological or Community diversity has three different levels: Alpha
Diversity (within-habitat diversity); Beta Diversity (between habitat diversity along
environment gradient) and Gamma Diversity (combined alpha and beta diversity). The
environment exerts continual pressure to diversify the life through innovation, adaptation and
exploitation of new traditions. The most prominent consequence of ecological and
environmental processes (causing species multiplication) is the species diversity. Certain
ecological and evolutionary process creates the biological diversity. There are certain factors
that can influence these variations in the biological diversity such as environmental factors,
disturbances, environment heterogeneity etc. Fires and felling of the trees are the forest
associated disturbances that can affect the successive composition of the species. Under
favourable environmental conditions such as growth conditions, greater diversity is offered
by the plants and animals species. Insect diversity can be promoted by the high plant diversity
and the primary cause of this diversity relationship as the coevolution between insects and
plants involving secondary metabolites or chemicals. The high productive grasslands show
less diversity due to intense competition between species for light and there is negative
relationship indicating that soil fertility inversely affects the diversity. The “theory of island
biogeography” gives explanation for the species diversity on land and states that the number
of species inhabiting the island is inversely proportional to the distance between mainland
and given island and directly proportional to the size of the island.
Several metrics can be used to measure biodiversity such as number of species or species
richness; species evenness; genetic diversity; phenotypic variance and population number.
Species richness and evenness are the two main factors accounting for measuring diversity.
An increase in evenness and richness of species increases the diversity.

14

Principles of Ecology
ZOOLOGY Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part II