Transcript nested subsets or nestedness

Princip hnízdovitosti (nested subsets
or nestedness) druhového složení:
výpočet a ekologické interpretace
Michal Horsák
Ústav botaniky a zoologie
PřF MU Brno
Nested subset patterns of species
composition
• Theory
• Calculations
• Applications
http://aics-research.com/nestedness/tempcalc.html
http://fm1.fieldmuseum.org/aa/staff_page.cgi?staff=patterso&id=438
nestedness - theory
One of the main goals of community ecology is the
identification and explanation of non-random patterns of
species composition.
One of the patterns is the nestedness:
–
–
the nested subset hypothesis states that the species
comprising a depauperate insular biota are a proper
subset of those in richer biotas, and that an archipelago of
such biotas, ranked by species richness, presents a
nested series
a group of species assemblages is said to be perfectly
nested when each species is present in all assemblages
richer than the most depauperate one in which that
species occurs
nestedness - theory
Nested
A
B
C
Non-nested
A
C
B
nestedness - theory
Three conditions are necessary for development of
nestedness:
–
–
–
islands or sites must be ecologically comparable
species inhabiting these sites must have shared
similar biogeographic histories
species must be hierarchically ordered in terms of
their niches
The first two points correspond to homogeneity constrains.
The third condition serves to summarize factors that order
the incidence of species.
nestedness - theory
The nested pattern was first proposed by Darlington (1957):
Zoogeography, …colonization of islands only by species with
high dispersal capabilities.
Patterson & Atmar (1986): Nested subsets and the structure of
insular mammalian faunas and archipelagos.
Now nestedness has proved to be a very common
phenomenon - 219 papers since 1980, Web of Science
mammals, births, frogs, fish parasites, plants, dragonflies…
/archipelago = a geographically coherent cluster of islands, also clusters of
insular habitats or non-insular sites/
nestedness - theory
Degree of nestedness:
vertebrates >> invertebrates (especially aquatic), plants
- high diversity
- deferent origin and biogeographic histories
- highly variable environment
- scale dependence
Around 10 studies in freshwater systems:
- insects in Sweden (e.g. Malmqvist et al. 1999)
- macroinvertebrates in fragmented Alpine streams
(Monaghan et al. 2005)
- Bdelloidea, Ostracoda, Ephemeroptera, Plecoptera,
Trichoptera, Dytiscidae, Culicidae, Simuliidae
nestedness - theory
What becomes relevant is what mechanisms promote
nestedness in communities with different phylogenetic
and ecological attributes.
Several mechanisms were proposed:
– selective extinction
– selective colonization
– historical effects
– speciation
– differential reproductive success
– habitat nestedness
– nested habitat quality
– human disturbances
– sampling artefact
nestedness - calculation
Many different metrics of nestedness have put forward in
the last two decades (see Wright et al. 1998).
Two of the most used procedures are:
– “departures“ method of Lomolino (1996)
– “temperature“ method of Atmar & Patterson (1993)
Sfenthourakis et al. (1999) concluded that the later method
is more suitable for evaluating the level of nestedness.
nestedness - calculation
The temperature method of Atmar & Patterson (1993)
– their metric measure the heat of disorder
presence-absence
matrix
nestedness - calculation
Calculation the temperature of binary matrix involves three
steps:
1.
2.
3.
to compute an isocline of perfect order – it is a curve
that, in a perfectly nested matrix of the same size an fill,
would separate cells denoting the presence of a
species at a site from cells denoting its absence
to find the matrix using permuting rows and columns in
the way that maximizes its nestedness
to associate with each absence above the isocline and
with each presence below it a normalized measure of
distance to the isocline.
The temperature of the matrix is the sum of these
distances (normalized to range between 0 for a perfectly
nested matrix and 100 for a maximally unnested matrix).
nestedness - calculation
The temperature method of Atmar & Patterson (1993)
– their metric measure the heat of disorder
presence-absence
matrix
nestedness - calculation
Two forms of noise contribute to the matrix‘s temperature:
1.
the random variation of
different stochastic events
2.
the “coherent“ noise of
specific idiosyncratic
biogeographic events
–
idiosyncratic species
–
idiosyncratic sites
nestedness - applications
The phenonenon, termed nested subsets has various
biogeographical, ecological, and coevolutionary
consequences, as well as important implications for biological
conservation. (B.D. Patterson)
What the metric offers:
– a measures of the uncertainty in species extinction order
– a measures of relative populational stabilities
– a means of identifying minimally sustainable population size
– an estimate of the historical coherence of the species
assemblages
– a revelation of mechanism promoting the nestedness
– a decision for an appropriate conservation strategy
nestedness - applications
How to reveal a mechanism promoting the nestedness?
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to correlate the ranking order of sites in the final
nested matrix with the order of sites after re-arranging
the sites along the analysed factor
–
a significant correlation suggests that a community is
packed in a predictive order owing to the influence of
a given factor (Patterson & Atmar 2000)
nestedness - applications
Implications for biological conservation:
–
the SLOSS problem has been addressed in a large
number of studies (for details see Ovaskainen, 2002),
but no coherent conclusion has yet appeared
–
an important conclusion from previously published
studies is that the result depends on the level of
nestedness
–
if the biota is highly nested, "single large" is found to
be the better strategy. On the contrary, if the biota is
not nested the "several small" strategy tends to
maximize the number of species
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