Large scale patterns of biodiversity · Random set of pencil lengths with a constraint + bounded...
Transcript of Large scale patterns of biodiversity · Random set of pencil lengths with a constraint + bounded...
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Large scale patterns of biodiversity
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Elements of biodiversity
EcologicalBiomesBioregionsLandscapesEcosystemsHabitatsNichesPopulations
GeneticPopulationsIndividualsChromosomesGenesNucleotides
OrganismalKingdomsPhylaClassOrderFamiliesGeneraSpeciesPopulationsIndividuals
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The Ecological NicheGrinnell (1917) – the habitat or environment an organism can occupyElton (1927) – the role a species plays in the communityHutchison (1957) – quantify the abiotic and biotic dimensions of the niche
à an n-dimensional hypervolume
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Which axes define the niche?
• abiotic conditions• resources• limiting factors
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Condition/Resource Response Curves
Examples: temperature, pH, water
Intensity of Condition or Resource
Per
form
ance Reproduction
Growth
Survival
Survival not possible
Reproduction possible
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Diversity and the niche
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Elements of biodiversity
EcologicalBiomesBioregionsLandscapesEcosystemsHabitatsNichesPopulations
GeneticPopulationIndividualsChromosomesGenesNucleotides
OrganismalKingdomsPhylaClassOrderFamiliesGeneraSpeciesPopulationsIndividuals
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WHY SPECIES RICHNESS?
PracticalExisting informationSurrogacy - it is related to other measures
more species meansmore genetic diversity - genes-popnsmore organismal diversity - ind�s-higher taxamore ecological diversity - niches habitats etc
Wide application
But what is a species and how many are there?
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HOW MANY SPECIES ARE THERE?
We don�t know!
3 – 100,000 million species
BEST GUESS ca. 8.75 million Mora et al. 2011
total OceanEukaryoteAnimalia 7,770,000 2,150,000Fungi 611,000 5,320Plantae 298,000 16,600Chromista 27,500 7,400Protozoa 36,400 36,400ProkaryoteArchaea 455 1Bacteria 9,680 1,320
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Patterns – three examples
Patterns and the environment
à Hypotheses
Issues and Ideas
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Where do we find the most species?What patterns are there?
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Where do we find the most species?What patterns are there?
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How general is the latitudinal diversity gradient?
Meta-analysis
- a statistical technique to quantify overall effect from multiple studies
- weights studies by the sample size
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Meta-analysis
- a statistical technique to quantify overall effect from multiple studies
- weights studies by the sample size
1.5
1.0
0.5
0
-0.5
-1
-1.5
Mea
n E
ffect
�
95%
con
fiden
ce in
terv
al
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How general is the latitudinal diversity gradient?
Hillebrand (2004) - 600 gradients- local and regional scale- many organisms- many habitats
(terrestrial, marine, freshwater)- many realms
(New, Australasia, Eurafrica)
Assessed slope of line relating latitude and species richness
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local and regional scale
local – small spatial extent, < 1 m – few km2
area depends on organisms- area within which species likely to interact
regional – large spatial extent, many km2, multiple habitats and communities
- area within which speciation and extinction operate- area that provides the pool of species that can over
time colonize a local community
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local
local and regionalα-diversity, β-diversity, γ-diversity
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How general is the latitudinal diversity gradient?
Hillebrand (2004)
Effect = slope of best line
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Low Latitude HighEquator Pole
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How general is the latitudinal diversity gradient?
Hillebrand (2004)
Wide range of taxonomic groups -
mammals, birds, fish, copepods
Terrestrial and marine > freshwater
New world > Australasia and Eurafrica
Conclusion - ubiquitous pattern
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Patterns
Patterns (INDEPENDENT VARIABLE) and the environment (POSSIBLE EXPLANATORY VARIABLES)
à Hypotheses
Issues and Ideas
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Climate – primary productivity (evapotranspiration)
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ClimateWallace (1878)- the tropics have suffered fewer harsh events
+ Time - the tropics are older
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Area
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Why is there a latitudinal gradient in biodiversity?
Four general hypotheses
Null modelsMid-domain effect
Climate hypothesesSpecies – energy model
Historical hypothesesTime + perturbationTime and Area
Evolutionary hypothesesClimate stabilityEvolutionary speed theoryBiotic interactions hypothesis
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Null models – the mid-domain effect (Colwell and Hurtt 1994)
Random set of pencil lengths with a constraint
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+ bounded domain
Null models – the mid-domain effect (Colwell and Hurtt 1994)
N
S
Random set of species ranges
à ranges overlap more at centre than at limits
à more species in tropics
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Climate hypotheses for diversity gradients –species – energy hypothesis
Climate sets limit to richnessclimate in tropics (temperature + precipitation) à higher NPPhigher NPP à more individualsmore individuals à more species with viable pop’ns
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Historical hypotheses for diversity gradients
ExampleLake Baikal unglaciated lake 580spp benthic invertsGreat Slave Lake glaciated lake 4 spp
Time (Wallace 1878)
CatastrophesEg glaciation
Tropics
Temperate
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Historical hypotheses for diversity gradients
Tropical environments are olderàmore time for diversity to accumulate
Tropics have a larger “area” when considering earth’s history
Time and Area Hypothesis
Larger areas = larger popns-----> less extinction
Larger areas = more barriers-------> more speciation
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Evolutionary hypotheses for diversity gradients –
The tropicsa “cradle” for the generation of new taxaand/ora “museum” for the preservation of existing biodiversity”àgreater diversification (speciation – extinction)
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Evolutionary hypotheses for diversity gradients –
Climate stability hypothesis
Tropics - predictable and mild à greater specialization/speciationà smaller niches à more species
High latitudes - unpredictable and severe à selection for flexibilityà larger niches and less speciationà less species per habitat
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evolutionary hypotheses for diversity gradients –
evolutionary speed theory (Rohde 1992)
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Evolutionary hypotheses for diversity gradients
Biotic Interactions hypotheses (Schemske 2002)
Biotic interactions (b) are a stronger selective force than abiotic factors (a) in the tropics à higher speciation
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Patterns
Patterns (INDEPENDENT VARIABLE) and the environment (POSSIBLE EXPLANATORY VARIABLES)
à Hypotheses
Issues and Ideas
Productivity, history and area, climate stability and temp. covaryOur hypotheses generate similar predictions
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Hypotheses
Mid-domain effectSpecies – energy modelTime – perturbationTime and AreaClimate stabilityEvolutionary speed theoryBiotic interactions
Some hypotheses are difficult to differentiate because they make the same predictions about speciation and extinction in the tropics and temperate regions
Spe
ciat
ion
Ext
inct
ion
x xx �x �� �� x � x � x
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Issues and Ideas
Currie et al. 2004 – should consider mechanism
Vellend - hypotheses for patterns based on lower level processeswill proliferate
- should consider higher level processesselection = selective loss of species (extinction)ecological drift = chance loss of species (extinction)dispersal = movement of speciesspeciation
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AdvancesSpecies – Energy Hypothesis (Currie et al. 2004)
i) higher NPP à more individualsii) more individuals à more species with viable pop’ns
i – true, but weak ii – true, but >> predicted
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AdvancesEvolutionary Speed Hypothesis (Rohde 2002)
i) higher Temp à faster molecular evolutionii) faster molecular evolution à more speciation
i – supported eg Oppold et al. 2016 PNAS
ii ltd data, weak relationshipeg Dugo-Cota et al 2015 Global Ecol Biogeogr
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# Spp. Latitudehigher nearer equator
lower nearer poles
Advances: phylogenetic approachesCardillo (1999)
So DIVERSIFICATION rate(speciation – extinction) is higher nearer the equator
9/10 pairs of birds clades-more southerly clade more species-rich
10/13 butterfly sister-group comparisons-more southerly clade more species-rich
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!
Advances: phylogenetic approachesRoland et al. 2014 - 5020 mammals from 8 orders
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Biodiversity and Area
Eg Lesser Antilles19 islands13 - 1510 km2
Species richness increases with island size
Alexander von Humboldt (1807)
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Patterns
Lesser Antilles19 islands13 - 1510 km2
Log (Area)
Log
(Num
ber o
f spe
cies
)
Fig 19.8 from Stillings text
Slope Z ~ 0.3
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Pattern on 61 islands off the coast of UK
z=0.32
r2 = 0.66
Log Area
Gaston and Blackburn 2000
Log
(Num
ber o
f spe
cies
)
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Pattern on 59 Woodland "islands" for birds in UK
z=0.28
Eastern Wood, Surrey
r2 = 0.82
Log Area
Note- the data in these figures are independent
Log
(Num
ber o
f spe
cies
)
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(Gaston & Blackburn, 2000)
Other species-area data can be nested
these data are not independent
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Species –Area RelationshipsHypotheses/models and Processes
MacArthur and Wilson (1967) - Island biogeography theory
Processes - ?
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Species area curves for birds and mammals
Forest mountaintops in the Great Basin of the western USA
Boreal birdsZ=0.165
Boreal mammalsZ=0.326
Q. What is different about birds and mammals?
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Islands vs mainland isolation àdifferent islands more different than different areas of mainlandàgreater slope
Dispersal distance greater dispersal ability (of taxonomic group) à greater homogeneity
àtaxa with smaller slope
Latitude gradient in diversity and turnover
Factor mechanism
What could influence the slope (z)?
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Meta-analysis: 794 Species Area Relationships –Result 1. Nested > IndependentResult 2. SAR on islands = SAR on mainlandResult 3 and 4 (see figs)
Slop
e (z
) of
SAR
Drakare et al. 2006
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Applying species area curves to conservation
Change Proportion remaining
Log(Area)
Log(
#Spe
cies
)
a A
Log(S)
Log(s)
s/S = caz/cAz
= az/Az
= (a/A)z
WHAT SLOPE OR Z DO YOU USE?estimate from nested SARdepends on taxa – and their dispersal capacity (body size)depends on location (latitude) – due to latitudinal gradient
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�…rarity is the attribute of vast numbers of species in all classes…�
Charles Darwin 1859
American moon moth Tiger longwing
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Relative abundance of Lepidoptera in Rothamsted, UK
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Types of species abundance diagrams
107
106
105
104
103
102
Most abundant least abundant
Geometric series - least equitable
Broken stick - most equitable
Log-normal
Rank
Log 1
0(ab
unda
nce)
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Examples of lognormal distributions
lengths of words in phone conversationssize of sand grains on a beachlength of latency period for infectious diseases
Does ecology play any role in species-abundance relationships?
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Ecological explanations are based on niche models1. the sequential breakage hypothesis - Sugiwara 1980
The
nich
e sp
ace
+hierarchical community organisation
Lognormal
Species 1 2 3 4
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Ecological explanations 2. the broken stick - MacArthur 1957
The niche space
Broken-stick
Colonists arrive Resources are dividedRandomly at one time
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Ecological explanations 3. the geometric series - Whittaker 1970
The niche space
+each successive spp takes a fixed fraction
geometric
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Species abundance patterns
of many biological communities fit the log-normal dstribution
may be explained by niche apportionment models (see Wikipedia entry)
BUT
Are hypotheses linking niche organisation and species abundance testable?
What two pieces of information would you need?
What predictions can be generated from these pieces of information?
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Testing the connection between hierarchical niche organisation and species abundance
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base upper
middle 1/3 upper 1/3
inner outer inner outer
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Testing the connection between hierarchical niche organisation and species abundance
Dendogram of niche similarity
Corresponding process by whichniche space is split
Sugihara et al 2003 PNAS 100 5246-5251
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Testing the connection between hierarchical niche organisation and species abundance
Prediction 1Spp highly nested should be less abundant than spp on undivided branches
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Dendogram of niche similarity
Niche splitting
1
2
3
What is the expected abundance distribution?
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Prediction 2 Even distributions are associated with even niche dendograms
Species rankRela
tive
abu
ndan
ceTesting the connection between hierarchical niche organisation and species abundance
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Testing the connection between hierarchical niche organisation and species abundance
Sugihara et al. 2003DATA: 11 communities with niche dendograms and
species abundance data
Waterfowl, Fish, Amphibians, Lizards, Songbirds
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Testing the connection between hierarchical niche organisation and species abundance
Prediction 1Abundance declines with increasing nestedness in 10 of 11
Overall p = 0.012
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Testing the connection between hierarchical niche organisation and species abundance
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Empirical data support generality of Lognormal distributions
Hierarchical niche models such as sequential breakage hypothesis have some support
Opponents argue1) Species abundance is inappropriate if species differ in mass 2) resources will be divided amongst species from many taxa not only those from a single taxonomic group
So WHY/HOW we have/get lognormal distributions is much debated
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Three PatternsLatitudinal gradients in diversitySpecies area relationshipsSpecies abundance distibutions
Many models
With some thought to mechanism null modelsfirst order processes
– Speciation, dispersal, selection and ecological drift
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References
Mittelbach (2018) Commnity Ecology – Ch 2.
Worm and Tittensor (2018) A Theory of Global Biodiversity. Princeton University Press
Currie et al. (2004). Predictions and tests of climate-based hypotheses of broad-scale variation in taxonomic richness. Ecol Lett 7: 1121–1134
Schemske and Mittelbach (2017). “Latitudinal Gradients in Species Diversity”: Reflections on Pianka’s 1966 Article and a Look Forward. Am Nat 189: 599-603
Eric Pianka typing his thesis
Selected readings
Latitudinal gradients or Species abundance distributions
Species-area relationships will be revisited during discussions of Neutrality