Princip hn

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Princip hnízdovitosti (nested subsets or
nestedness) druhového složení výpocet a
ekologické interpretace
Michal Horsák Ústav botaniky a zoologie PrF MU
Brno
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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
pattersoid438
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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

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nestedness - theory
Nested
Non-nested
A
C
B
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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.
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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/
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nestedness - theory
Degree of nestedness vertebrates gtgt
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
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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

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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.
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nestedness - calculation

• The temperature method of Atmar Patterson
  (1993)
• their metric measure the heat of disorder

presence-absence matrix
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nestedness - calculation
Calculation the temperature of binary matrix
involves three steps

• 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).
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nestedness - calculation

• The temperature method of Atmar Patterson
  (1993)
• their metric measure the heat of disorder

presence-absence matrix
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nestedness - calculation
Two forms of noise contribute to the matrixs
temperature

• the random variation of different stochastic
  events
• the coherent noise of specific idiosyncratic
  biogeographic events
• idiosyncratic species
• idiosyncratic sites

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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

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nestedness - applications

• How to reveal a mechanism promoting the
  nestedness?
• 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)

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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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