LSM2251-09 Species Abundance & Diversity

8/3/2019 LSM2251-09 Species Abundance & Diversity

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Community Ecology

Species Abundance andDiversity

Li Daiqin

National University of Singapore

LSM2251

Ecology and Environments


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Objectives - After studying this

lecture you should be able to

!! describe the properties that define the structure ofcommunity"! the concepts of species richness, relative abundance or

evenness, and diversity

!! know how to study species diversity

!! start thinking about the processes that influence thestructure and dynamics of communities


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Outline

!! Introduction!! Species diversity!! Species abundance

"! Lognormal distribution!! Quantitative index of species diversity!! Environmental complexity!! Disturbance and diversity

"! Intermediate disturbance hypothesis


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Introduction

!! Habitat:The place where an organism lives

!! Community: A collection of all interacting specieslocated in a particular geographical area (habitat).

!! Guild: Group of organisms that all make their livingin the same fashion."! e.g. seed eating animals in the desert.

!! Life form: Combination of structure and growthdynamics."! e.g. tree, shrubs, forbs, grasses


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Introduction, contd

!! Thecentral issuein community ecology

"! What factors are most important instructuringacommunity -- in determining its speciescomposition and abundance of species present?

!!Community structureincludes attributessuch as number of species, the relativeabundance of species, and the kinds ofspecies


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Introduction, contd

!! The factors that shapecommunity structure

"! interactions between climate and topography"! the kinds and amount of resources over the time"! individuals adaptive traits"! species in the habitat interact"! overall patterns and actual history of abiotic an

biotic environment


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Species Diversity

!! Species diversity component

"!Species richness (S): the total number of species

present in a community

"!Relative abundance or evenness: a measure ofthe apportionment or allotment of individuals

among species

!! not all species are equally abundant! Why?


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Species Diversity, contd

!! Measurement of diversity has typicallyfocused on:

"! Number of species present"! Relative abundance of these species"! Some combination of number and abundance


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Species Diversity, contd!!Species richness (S)

"! What is it?!! The total number of species present

"! How to measure it?!! As simple as making a list

"! Global patterns of species richness (next lecture)"! Commonly used, but there is one major problem:

Example 1 No. of

individuals ofspecies 1

No. of

individuals ofspecies 2

Species

richness(S)

Total No. of

individualsCommunity A 99 1 2 100

Community B 50 50 2 100


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!!Species richness is highly susceptible to samplesize

"!You will find more species if you sample a larger area

!! implies that only counts of species from equal areas aredirectly comparable

!! some (not all) of this effect is a consequences of havingexamined more individuals


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!! When numbers dont tell the entire story..."! Consider two communities, each with same 5

species, compared with equal samples of25individuals -- which is more diverse?

1.! Example 2:!! Community A B"! species 1 21 5"! species 2 1 5"! species 3 1 5"! species 4 1 5"! species 5 1 5"! Total 5 25 25


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Species Diversity, contd Species evenness


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Species Diversity, contd Species evenness

!! When numbers dont tell the entire story...

"! Abundance patterns may complicate thedetermination of richness

"! Note that a species-poor, but even communitymay appear richer than a species-rich, but

uneven community at small sample sizes

"!Both species richness and abundance should thusbe incorporated in measures of species diversity


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Species Abundance!! Species abundance

"! Commonness or the number of species and the number ofindividuals of each species in a community!! Most concerned withrelative abundance of species

"! The proportion that a particular species contributes to the totalabundance of a community

!! e.g., for species A, the relative abundance is 0.25 (25 individuals/100individuals for 5 species)

!! Question:"! What can I see (a pattern of the abundance of species) if I go out

to study a community and quantifythe abundance of specieswithin a group of organisms in question such as spiders, butterflies,shrubs, or birds?

!! What can you see?"! There areregularitiesin the relative abundance of species in

communities that hold regardless of the ecosystem.


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Species Abundance, contd

The Lognormal Distribution

!!Preston(1948, 1962a, b) graphedabundance of species in collections as

frequency distributions.

"! Lognormal distributions!! Bell-shaped, or normal curves.

"! In most lognormal distributions, only portion of bell-shapedcurve is apparent.

#! Sample size has large effect.#! Significant effort is needed to discover rare species.


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Lognormal distributions (bell-shaped) of (a) desert plants,

and (b) forest birds. Note that the x-axis is on a log2 scale.

Most species are moderately abundant and few are

very abundant or extremely rare

Molles, M.C. Jr. 2010.Ecology: concepts and applications, 5rd ed. McGraw-Hill.


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Effect of sample size on the lognormal distribution

!! Questions:"! So, why do smaller sample

size result in only a part of

the bell-shaped curve (see

(a))?

"! Why does the massivesampling efforts reveal

only a portion of the bell-

shaped curve as well (see

(b))?"! Is the lognormal

distribution important?

Why?


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Sample-based rarefaction curves of the butterfly communities of forest

reserves (FR), forest fragments (FF), urban parks adjoining forests (PF),and isolated urban parks (IP) in Singapore using EstimateS version 6.0b

(Data from Koh & Sodhi 2004)

Koh & Sodhi. 2004. Ecol. Appl. 16: 1696-1708


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Lognormal Distribution

!! How does this lognormal distribution occur? - does itreflect important biologicalprocesses?

!! May(1975) proposed lognormal distribution is astatistical expectation- a product of variousrandom environmental variables acting on manyspecies within a community.

!! Sugihara(1980) suggested that lognormaldistribution is a consequence of the species within acommunitysubdividing niche space.


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Quantitative Index of Species Diversity!! A variety of diversity indices in two broad

categories:"! Dominance indices

!! Berger & Parker index:DBP= Nmax/N; where Nmax = the number ofindividuals in the most abundant species"! Community A in example 2:DBP=21/25 =0.84"! Community B in example 2:DBP=5/25 =0.2"! While community B is more diverse than community A, it has a lower value ofDBP.

"! Thus, to express greater diversity, we usually use D = 1/DBP."! Advantage: very easy to calculate"! Disadvantage: ???

!! Simpsons index:Ds=![(ni(ni- 1))/(N(N - 1))];where ni = number of individualsin theith species, N = total number of individuals in the community

"! Like Berger & Parker index, the higher the value ofDs,the lower is the diversity."! So, Simpsons index is usually expressed as 1/Dsor 1-Ds."! Advantage: use information from a broader array of species, thus more accurate."! Disadvantage: many rare species with one individual (very common) has no

contribution to diversity index value. Limited use in conservation biology. Why?

!! Common species influence estimates of diversity fromdominance indices more heavily than do rare species.


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Quantitative Index of Species Diversity

!! A variety of diversity indices in two broadcategories:"! Information-statistic indices

!! Brillouin index:HB= [ln (N!) -!ln (ni!)/N]!! Shannon index: One of the most widely used indices

s

!!H = -!(pi)(log pi) i=1

Where:

H= Shannon diversity index

pi

= the proportion of theith species

i=ith species

S = number of species


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Species (i) Abundance ni! ln(ni!)1 5 120 4.792 5 120 4.793 5 120 4.794 5 120 4.795 5 120 4.79

Total S= 5 N = 25 !ln(ni!) = 23.95

Example 1: Brillouin index

Therefore,HB= [ln(N!) -!ln(ni!)]/N= [ln(25!) 23.95]/25 = 1.362

Quantitative Index of Species Diversity, contd


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Species (i) Abundance pi piln pi1 50 0.5 -0.3472 30 0.3 -0.3613 10 0.1 -0.2304 9 0.09 -0.2175 1 0.01 -0.046

Total 5 100 1.00 -1.201

Example 2: Shannon index

Therefore, H = -! pi ln pi = - (-1.201) = 1.201. Note that even the

rare species with one individual, species 5, contributes some value

to the index. Think about what if an area has many rare species?


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Example 3: Shannon index vs Brillouin index

Species Individuals insample 1

Individuals insample 2

1 3 5

2 3 5

3 3 5

4 3 5

5 3 5

H 1.609 1.609HB 1.263 1.362



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!! Information-statistic indices!! Take into account rare species!! Difference between Brillouin index and Shannon index:

"! Shannon index does not change with species abundance(example above) while Brillouin does.

#! Brillouin index discriminates between two communitieswith the same number of species and their proportionalabundance while Shannon index does not, thus better

discriminant ability.

#! Brillouin index have some real advantage over Shannonindex and may be preferably in conservation biology.

"!Calculation: Shannon index is relatively easy.

With at least 5 indices (many others), so which index

should we use? Take a look at example 4.


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Example 4: Abundance of bird species on unrestored tin-mining areas, in restored areas and in unmined

pristine forest areas of Indonesia. Data from Sterling (2002)Unrestored sites Second-year restored sites Unmined

Yellow-vented bulbul 7 11 44

Olive-backed sunbird 5 10 12

Ashy tailorbird 2 3 20Spotted dove 1 4 8

Orange-bellied flower-pecker 1 3 8

Blue-throated bee-eater 0 4 5

Cuckoo doves 2 0 4

Magpie robin 0 0 13

Less coucal 0 1 5

Plaintive cuckoo 0 0 7

Savanna nightjar 3 4 0

White-headed munia 3 4 0

Scaly-breasted munia 0 0 0

Richards pipit 2 0 0

Red-eyed bulbul 0 0 6

Woodpecker 0 0 4

Black-shouldered kite 0 0 4

Striped tibabbler 0 0 4

Large-tailed nightjar 0 0 0

Eastern marsh harrier 0 0 1

Scarlet-backed flower pecker 0 0 1

Species richness (S) 9 9 16


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Calculation of the Berger-Parker, Shannon, and Brillouin indices for the data in

Example Data from Sterling (2002)

Unrestoredsites Second-yearrestored sites Unmined

Berger-Parker (DBP) 3.72 4.0 3.32

Simpson (Ds) 8.83 7.76 7.91

Shannon (H) 1.81 2.02 2.32

Brillouin (HB) 1.62 1.88 2.16

"!The same general trend that restored sites are more diverse thanunrestored sites.

The value of Simpsons index does not indicate this trend, showing

that, on occasion, different indices can give different results.

Results vary according to the particular distribution of individuals

among species.


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A comparison of the effectiveness of different diversity indices

Index DiscriminantabilitySensitivityto sample

sizeBiased towardrichness (R) ordominance of afew species (D)CalculationWidelyused

Species richness (S) Good High R Simple YesShannon (H) Moderate Moderate R Intermediate YesBrillouin Moderate Moderate R Complex NoSimpson Moderate Low D Intermediate YesBerger-Parker Poor Low D Simple No!There is no one single best diversity index. Ones choice of index oftendepends on the question asked!

! Dont mix diversity indices when comparing communities - you cannotcompare community using a Shannon index for one and a Simpsons index

for another - must use one index throughout.


- so which index should I use?


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!! Diversity indices may be used to comparespecies diversity

"! within a community ("-diversity)

"! between communities (#-diversity)

"! among communities over a wide geographicalarea ($-diversity)


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Rank Abundance Curves, Contd


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Rank Abundance Curves of Caddisflies

(Insecta: Trichoptera) from northern Portugal


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Rank Abundance Curves of Caddisflies

Molles, M.C. Jr. 2010.Ecology: concepts and applications, 5th ed. McGraw-Hill.

Caddisflies are

aquatic insects. Morecaddiflies are in astream, the better

quality of water is.

Coastal ponds at Mira

containing 18 species, whilemountain stream at Relva

having 79 species


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Environmental Complexity

!! In general, species diversity increases withenvironmental complexity or heterogeneity.

!! MacArthur(1958) found warbler diversityincreased as vegetation stature increased."! Measured environmental complexity as foliage

height.

!! Many studies have shown positive relationshipbetween environmental complexity andspecies diversity.


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Forest Complexity and Bird Species Diversity


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Foliage Height Diversity and Bird Species

Diversity


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Heterogeneity and Diversity of

Tropical Forests

!! Jordan(1985) studied the relationship betweenvegetation and soils in Amazon forest and

concluded that tropical forest diversity is organized

in two ways:

"! Large number of species live within most tropical forestcommunities.

"! There are a large number of plant communities in a givenarea, each with a distinctive species composition.


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Molles, M.C. Jr. 2010.Ecology: concepts and applications, 5th ed. McGraw-Hill.

Soil and Topographic Heterogeneity and

Diversity of Tropical Forest Trees


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Plant Species Diversity and Increased Nutrient

Availability - Negative Relationship

!! Repeatedly observed negative relationship between nutrientavailability and algal and plant species diversity.

!! Adding nutrients to water or soils generally reduces diversity of plantsand algae.

"! Reduces number of limiting nutrients.


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Disturbance and Diversity

!! Disturbance difficult to define as it involvesdeparture from average conditions.

"! Average conditions may involve substantialvariation.

!!Sousa(1979) defined disturbance:"! Discrete, punctuated, killing, displacement, or

damaging of one or more individuals that directly

or indirectly creates an opportunity for new

individuals to be established.


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Disturbance and Diversity

!!WhiteandPickettdefined disturbance:"! Any relatively discrete event in time that disrupts

ecosystem, community, or population structure

and changes resources, substrate availability, or

the physical environment.

"! Two major characteristics:!! Frequency!! Intensity


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Intermediate Disturbance HypothesisIntermediate levels of disturbance maximize the number of

organisms from different successional stages


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Intermediate Disturbance Hypothesis

!!Connell(1975, 1978) proposed disturbanceis a prevalent feature that significantlyinfluences community diversity.

"! Proposed both high and low levels of disturbancewould reduce diversity.

!! Intermediate levels promote higher diversity."! Sufficient time between disturbances allows wide variety of

species to colonize, but not long enough to allowcompetitive exclusion.


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Disturbance and Diversity in the

Intertidal Zone

!! Question: how does disturbance (ocean wavesgenerated by winter storms) affect on diversity of algaeand invertebrates growing on boulders in the intertidalzone."! Sousa, W.P. (1979).Ecology60: 1225-1239.

"! Prediction: level of disturbance depends on boulder size.!! Large boulders require more force to move, thus less

disturbance; smaller boulders are turned over more frequently,thus high frequent disturbance.


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Disturbance and diversity of marine algae andinvertebrates on intertidal boulders

Boulders subject to intermediate levels of disturbancesupport greatest diversity of species.


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Applications: Disturbance by Humans

!! Human disturbance is an ancient feature of thebiosphere.

!! The effects of human disturbance fall within theframework of the intermediate disturbance hypothesis.

!!Human disturbance threatens many species withextinction.

!! Moderate human disturbance may also increase speciesdiversity.


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Figure 16_22


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Changes in number of plant species and coverage by the

grassBrachypodium pinnatum following abandonment of chalk

grassland in Netherland


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Applications: Disturbance by Humans

!! Whether could be declines in grassland diversity be reversed usingtraditional mowing?"! Bobbink and Willems (1987, 1991)."! Normal autumn mowing and summer mowing

!! Results:"! Summer mowing: biomass of grass decreased 77% to 34%; number of

plant species increased from 15.6 to 21.2/0.25m2

"! Autumn moving: grass biomass remained at 75-80%; number of plantspecies remained low.

!! How do summer and autumn mowing differ in their effects on grass?"! Four different mowing: (1) autumn; (2) later summer; (3) early summer;

or (4) early summer and autumn.

"! Results: two mowing greatly reduced grass biomass.!! Why is autumn mowing not sufficient for restoring the diversity of

plants?


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Take-home message

!! Most species are moderately abundant; few arevery abundant or extremely rare.

!! A combination of the number of species (i.e.,species richness) and their relative abundance(or species evenness) defines species diversity.

!! Lower slope of rank-abundance curves indicateshigher species evenness or richness

!! Species diversity is high in complexenvironments.

!! Intermediate level of disturbance promoteshigher species diversity.


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LSM2251-09 Species Abundance & Diversity

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