okt. 2007
I x T = P
31-10-2007 17:46
This seems like a
cryprtic formula, but it is utterly simple: Ideas x
Time available = Priorities needed. When studying
literature or when in contact with others ideas can
spring to mind, not to mention the creative flow that
can emerge from under the shower :-) Sometimes these
ideas need time to take shape in a form that allows
research, sometimes it is immediately clear that an
idea is worthwhile to implement. The latter situation
occurred this week when I was emailing to Mónica Vera
about her application for a visiting scholarship to
the Field Museum. When she was looking to make her
proposal more specific, it immediately came to mind
that making a revision of Plekocheilus
would be a good idea
that could serve several purposes: a) her application
for a scholarship, b) the on-going research for
making a checklist of Colombian land snails, c) our
planned study of the Guayana Shield malacofauna and
the speciation processes in that area. So, one more
project added to the "wish list".
Fortunately, another project is nearing completion. My study of Orthalicidae from Ecuador is entering the reviewing phase. I will solicit the critical review of some colleagues before I submit the paper to a journal.
Fortunately, another project is nearing completion. My study of Orthalicidae from Ecuador is entering the reviewing phase. I will solicit the critical review of some colleagues before I submit the paper to a journal.
Making progress, steadily but slow
28-10-2007 22:48
The
focus in the Ecuadorian project is now on the
analysis of the distributions. I decided first to pay
more attention to the analysis of ecoregions and
endemism. The latter concept is clearly contextual
and I was tossing around with it when I found an
interesting site that gave me some inspiration:
the Andes-Amazon project
in
Peru and Bolivia. This project deals with plants,
mammals, birds and amphibians, but in their
methodology they also used Maxent modeling. The
limited data on land mollusks (i.e. Orthalicidae)
makes it necessary to tailor-made a definition on
range-restricted species. I decided to limit it to
those species known from a single locality. Those
that are endemic to Ecuador deserve special
attention, and when I plotted their localities
three geographical clusters appeared. But clearly
more research is needed before any definite
conclusions can be drawn.
With my limited time (usually only during the weekends), progress is necessarily slow. So much to do and so little time...
With my limited time (usually only during the weekends), progress is necessarily slow. So much to do and so little time...
With some help and inspiration
13-10-2007 19:55
The Maxent package I
previously wrote about has a - like most freeware
software - a discussion group
which in my case was
helpful to solve some initial problems. One
problem - the grid output file that should be
suitable for input in DIVA-GIS - was a bug in the
beta version that I ran and was fixed very swiftly
by the Steven Phillips, the main author. After
this I could use the software to do useful
analyses on the Ecuadorian data. The result is a
series of distribution maps on (sub)generic level.
Although several studies (e.g. Elith et al., 2006;
Pearson et al., 2007) have shown that Maxent is
robust enough to handle datasets with only a few
occurrences per species, I preferred to do the
analyses on aggregated data to get a more
comprehensive result. Here is one of the maps,
obtained by processing the grid output file of
Maxent in DIVA-GIS.
Ecological niche model for Plekocheilus. The blue dots are localities where the genus is present. Colours represent logistic values of likelihood for occurrence: from 0-0.2 (dark green) to 0.8-1.0 (red).
When I out of curiousity tried to feed Maxent with occurrence data (also Plekocheilus) from the Guayana Shield, the resulting picture of the distribution showed a remarkable disjunct pattern. An inspirational indication that my hypothesis about linkages between the Pantepui region in Venezuela and the Andes in Colombia is worth further investigation!
Ecological niche model for Plekocheilus from Venezuela, Pantepui, as depicted by Maxent.
This even becomes more clear when all the known localities of Plekocheilus from Venezuela are taken into account.
Ecological niche model for all Plekocheilus known from Venezuela, as depicted by Maxent.
See also this blog for comments on Maxent.
References:
Elith, J. e. a. (2006). Novel methods improve prediction of species' distributions from occurrence data. Ecography, 26, 129-151.
Pearson, R. G., C.J. Raxworthy, M. Nakamura & A. Townsend Peterson. (2007). Predicting species distributions from small numbers of occurrence records: a test case using cryptic geckos from Madagascar. J. Biogeogr, 34, 102-117.
Ecological niche model for Plekocheilus. The blue dots are localities where the genus is present. Colours represent logistic values of likelihood for occurrence: from 0-0.2 (dark green) to 0.8-1.0 (red).
When I out of curiousity tried to feed Maxent with occurrence data (also Plekocheilus) from the Guayana Shield, the resulting picture of the distribution showed a remarkable disjunct pattern. An inspirational indication that my hypothesis about linkages between the Pantepui region in Venezuela and the Andes in Colombia is worth further investigation!
Ecological niche model for Plekocheilus from Venezuela, Pantepui, as depicted by Maxent.
This even becomes more clear when all the known localities of Plekocheilus from Venezuela are taken into account.
Ecological niche model for all Plekocheilus known from Venezuela, as depicted by Maxent.
See also this blog for comments on Maxent.
References:
Elith, J. e. a. (2006). Novel methods improve prediction of species' distributions from occurrence data. Ecography, 26, 129-151.
Pearson, R. G., C.J. Raxworthy, M. Nakamura & A. Townsend Peterson. (2007). Predicting species distributions from small numbers of occurrence records: a test case using cryptic geckos from Madagascar. J. Biogeogr, 34, 102-117.