Transcript ppt

Origins & Maintenance of Diversity
A Hierarchy of Processes
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Processes operate on a variety of
temporal & spatial scales to
influence diversity
The levels are nested
Unique (chance) events may occur
at any level
Figure 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
A Hierarchy of Processes
Biotal
interchange
Species
production
Regional
diversity
Stochastic
extinction
Habitat
selection
Mass
extinction
Local
diversity
Competitive
exclusion
Predatory
exclusion
A major challenge confronting advances to a research program that investigates
this multi-scale set of processes is the reconstruction of historical events
So, community ecologists have added phylogenetic & biogeographic analyses
(e.g., phylogeography) to their toolkits…
Redrawn from figure 30.1, Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Losos (1996)
“If species adapted rapidly and without constraint, and if any lineage could occur
in any community, then we would expect differences in community structure to be
indicative of environmental differences. Because lineages differ in their
evolutionary potential and are geographically restricted, however, comparisons of
community structure must take account of communities’ histories…”
“…differences in the structure of communities may result as much from the
differences in the lineages that occur in different communities as from differences
in environmental conditions”
“Phylogenetic information about the constituent lineages in a community can
allow lineage effects to be factored out, thus allowing an assessment of
environmental determinants of community structure”
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Ricklefs & Schluter (1993)
An example from passerine
birds compared between
Panama and Illinois: Why do
different areas vary in species
richness of particular clades?
“The approximately twofold
difference in average age of the
taxa matches the twofold
difference in diversity, although
age and diversity are not well
correlated among individual
clades.”
Table 30.2 from Ricklefs & Schluter (1993)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Losos (1990, 1996)
An example from Anolis lizards inhabiting Caribbean islands:
Where & under what community conditions did patterns of niche-use originate?
Origins & Maintenance of Diversity
Phylogenetic Perspectives
27 islands of the Lesser Antilles
contain either one or two species
of Anolis lizards; on 9 of the 10
two-species islands, the species
differ considerably in size (one
large & one small), whereas on
16 of 17 one-species islands, the
species are intermediate in size
Figure from Losos (1996)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Hypotheses:
(1) “Size adjustment (character displacement): Species of similar size
colonize an island & evolve in opposite directions in situ to minimize resource
competition”
From Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Size adjustment
Large
2
Large
2
Large
2
Small
2
Small
2
Small
2
(Int. 1)
(Int. 1)
(Int. 1)
(Int. 1)
Int.
1
Int.
1
Int.
1
(Int. 1)
Int.
1
(Int. 1)
(Int. 1)
(Int. 1)
(Int. 1)
Increase in size
Decrease in size
Switch to 2-species island
Redrawn from Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Hypotheses:
(1) “Size adjustment (character displacement): Species of similar size
colonize an island & evolve in opposite directions in situ to minimize resource
competition”
(2) “Size assortment: Competitive exclusion or other processes prevent
similar-sized species from colonizing the same island; only species that are
already dissimilar in size can successfully colonize and coexist”
From Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Size assortment
Large
2
Large
2
Large
2
Small
2
Small
2
Small
2
(Small 1)
(Large 1)
(Large 1)
(Small 1)
Int.
1
Int.
1
Int.
1
(Int. 1)
Int.
1
(Int. 1)
(Int. 1)
(Int. 1)
(Int. 1)
Increase in size
Decrease in size
Switch to 2-species island
Redrawn from Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Size assortment & size adjustment
Large
2
Large
2
Large
2
Small
2
Small
2
Small
2
(Small 2)
(Large 2)
(Large 2)
(Small 2)
Int.
1
Int.
1
Int.
1
(Int. 1)
Int.
1
(Int. 1)
(Int. 1)
(Int. 1)
(Int. 1)
Increase in size
Decrease in size
Switch to 2-species island
Redrawn from Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
No evidence for size assortment or size adjustment
Large
2
Large
2
Int.
2
Small
2
Small
1
Small
1
(Small 1)
(Large 2)
(Int. 2)
(Small 1)
Int.
1
Int.
2
Small
1
(Int. 1)
Int.
1
(Int. 1)
(Int. 1)
(Int. 1)
(Int. 1)
Increase in size
Decrease in size
Switch to 2-species island
Redrawn from Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
“In the northern Lesser Antilles,
large & small size appear to have
evolved simultaneously when two
lineages came into sympatry…
exactly the prediction of a
hypothesis of character
displacement…”
Figure from Losos (1996); quote from Losos (1990)
Dominica
Origins & Maintenance of Diversity
Phylogenetic Perspectives
“By contrast, in the southern
Lesser Antilles, evolutionary
change in body size appears to
have been unrelated to whether a
species occurred in sympatry
with congeners…
Dominica
Martinique
Consequently, the existence of
size patterns must have resulted
from a process of ecological
sorting in which only dissimilarsized species can successfully
colonize and coexist on the same
island…”
Figure from Losos (1996); quote from Losos (1990)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
“Thus, the relative importance of
co-evolutionary processes in
determining community structure
differs between the northern and
southern Lesser Antilles, a result
that is only apparent when these
lizards are studied in a historical
[phylogenetic] context”
Figure from Losos (1996); quote from Losos (1990)
St. Maarten
St. Eustatius
Dominica
Martinique
Origins & Maintenance of Diversity
Phylogenetic Perspectives
McPeek (1995)
An example from damselflies inhabiting freshwater lakes:
Where and under what community conditions did patterns of niche-use originate?
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Numbers represent the amount of evolutionary change in limb length between
ancestor & descendant, as deduced using parsimony methods for
reconstruction of ancestral character states
Redrawn from Losos (1996), based on McPeek (1995)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
The common ancestor inhabited lakes occupied by fish,
where its best strategy to avoid predation was to hide
Redrawn from Losos (1996), based on McPeek (1995)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Bars represent transitions to fishless lakes, where a damselfly’s best
strategy to avoid predation by dragonflies is to swim or run away
Redrawn from Losos (1996), based on McPeek (1995)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
An example from Neotropical snake assemblages: For areas that differ in the
species richness of particular clades, do contrasting characteristics of those
clades contribute to emergent community-level properties?
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
Observations:
Three main lineages of
Neotropical snakes within
the family Colubridae
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
Observations:
Principal
zones of
radiation
Three main lineages of
Neotropical snakes within
the family Colubridae
The xenodontine lineages
originated & diversified
relatively isolated from
one another, even though
the current distributions
overlap substantially
Colubrines
radiated
relatively
recently
worldwide
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
Observations:
Three main lineages of
Neotropical snakes within
the family Colubridae
The xenodontine lineages
originated & diversified
relatively isolated from
one another, even though
the current distributions
overlap substantially
The lineages differ in
mean body size, diet, and
etc.
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
An example from Neotropical snake assemblages: For areas that differ in the
species richness of particular clades, do contrasting characteristics of those
clades contribute to emergent community-level properties?
Observation:
Sites in Central & South America differ in body size distribution, diet & etc. of
their snakes, but those differences are largely due to differences in the dominant
clades occupying those sites
Conclusion:
The overall size distribution, diet & etc. of a community bears a direct
relationship to the clade composition (i.e., history matters)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Cadle & Greene (1993)
An example from Neotropical snake assemblages: For areas that differ in the
species richness of particular clades, do contrasting characteristics of those
clades contribute to emergent community-level properties?
Suggested a reinterpretation of patterns (e.g., no “goo-eaters”) from Brazilian
caatinga…
In contrast to Vitt and Vangilder
(1983), “we do not need to ‘explain’
the absence of invertebrate-eating
snakes [in the caatinga community]
in terms of present-day ecological
factors if historical events resulted in
the absence of appropriate lineages
from the community”
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Losos (1996), after Brooks & McLennan (1991, 1993)
“Four components contributing to community structure”:
1. Species that interact in the same way that their ancestors did in other
communities
2. Species that colonized a community but did not lead to ecological shifts in
residents (new associations of lineages, but ancestral ecologies were
maintained)
3. Species that arose in situ and evolved different ecological requirements
4. Species that colonized a community and interacted with species already
present, leading to ecological shifts in the colonizer, the resident, or both
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb et al. (2002)
“The differences among species that co-occur in an ecological community are
the result of modifications to a common ancestor that the species all ultimately
share”
Phylogenetic relationships provide “a new dimension of information… with which
to make sense of these differences among species”
Differences among species are due to divergence (either in sympatry or
allopatry), which may have occurred recently due to changes in the focal
species, or in the distant past due to changes in the ancestors of the focal
species
Similarities among species are either due to shared ancestry, or convergence
(either in sympatry or allopatry)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb (2000)
An example from rainforest trees: Is the distribution of species among habitats
(or samples) in a community nonrandom with respect to phylogeny?
“The demonstration of nonrandom spatial association of species with habitats is
a necessary but not sufficient criterion in demonstrating that habitat partitioning is
important in enabling many species to coexist…”
“However, to be able to show that co-occurring species in different habitats are
more ecologically similar than expected by chance would support the case that
species are partitioning habitat according to their autecology”
“On the other hand, if species in local communities were less ecologically similar
than expected by chance, this would suggest that negative neighborhood
interactions [e.g., competition] were causing increased mortality among
ecologically similar species…”
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb (2000)
Specific question: Are the tree species in 0.16-ha plots more or less related than
expected if such communities were formed from a random sampling of available
species in the larger area (150 ha)?
“…because of the conservatism of many species traits in the evolution of a
lineage, we expect, in general, a positive relationship between a measure of the
phylogenetic relatedness of two species and a measure of their overall lifehistory and ecological similarity…”
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb (2000)
What about character displacement?
“Under certain circumstances, where new niches are encountered (e.g., on
islands) or where competition with an ecologically similar species is strong and
predictable, particular ecological traits of an organism may change adaptively
over time… leading to a breakdown of the correlation between phylogenetic
relatedness and ecological similarity for some traits… However, even in these
organisms we would still expect that a measure of ‘overall’ ecological similarity,
taking many traits into account, would be correlated with phylogenetic
relatedness”
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb (2000)
Data: 28 tree plots of 40 x 40 m
(0.16 ha) scattered throughout
150 ha of lowland tropical forest,
Indonesia
How to efficiently estimate
relatedness?
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Webb (2000)
Data: 28 tree plots of 40 x 40 m
(0.16 ha) scattered throughout
150 ha of lowland tropical forest,
Indonesia
How to efficiently estimate
relatedness?
Created “supertrees” from
published phylogenies and
then counted nodes separating
terminal taxa
Greatest possible mean pairwise nodal distance for a
community of 4 taxa (given this phylogeny) = 3.66
nodes (for A, B, E, F)
Phylogeny
A
B
C
D
E
F
Community 1: A, B, C, D
Nodal distances:
A
A
B
C
B
1
C
2
2
D
4
4
3
Community 2: A, B, E, F
Nodal distances:
A
A
B
E
B
1
E
5
5
F
5
5
1
Mean pairwise nodal dist. =
(1+2+4+2+4+3)/6 = 2.66
Mean pairwise nodal dist. =
(1+5+5+5+5+1)/6 = 3.66
Net Relatedness Index =
1 - (2.66/3.66) = 0.273
Net Relatedness Index =
1 - (3.66/3.66) = 0.0
From Webb (2000)
Greatest possible mean nearest nodal distance for a
community of 4 taxa (given this phylogeny) = 2.00
nodes (for A, C, D, F)
Phylogeny
A
B
C
D
E
F
Community 1: A, B, C, D
Nodal distances:
A
A
B
C
B
1
C
2
2
D
4
4
3
Community 2: A, B, E, F
Nodal distances:
A
A
B
E
B
1
E
5
5
F
5
5
1
Mean nearest nodal dist. =
(1+1+2+3)/4 = 1.75
Mean nearest nodal dist. =
(1+1+1+1)/4 = 1.0
Nearest Taxa Index =
1 - (1.75/2.0) = 0.125
Nearest Taxa Index =
1 - (1.0/2.0) = 0.5
From Webb (2000)
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Methods:
Webb (2000) created 1000 sets of plots with randomized species membership,
following two simple rules: (1) each species occurred in the same total number
of plots as observed; (2) each plot contained the same total number of
species as observed
Randomized plots represent expected distributions of species if membership in
plots occurs at random with respect to the overall species pool of 324 observed
species throughout the 150-ha area
Compared the observed Net Relatedness Index (NRI) and the observed
Nearest Taxa Index (NTI) to the appropriate distributions of expected
values
Results:
The mean NRI did not differ significantly from the expectation of the null
hypothesis, but the mean NTI was significantly greater than expected
Origins & Maintenance of Diversity
Phylogenetic Perspectives
Conclusion:
Overall, species in the 0.16-ha plots were more likely to be found with species
separated by fewer nodes than expected by chance (e.g., congeners)
We can therefore reject the null hypothesis that species are assembled into local
communities at random; there is evidence that species occur with closely related
species more than we expect by chance
Environmental filtering? Primarily abiotic? Biotic? Trait-based?