[Taxacom] Biogeography and ecology excerpts

John Grehan calabar.john at gmail.com
Mon Dec 5 11:00:52 CST 2016

Below some excerpted general comments on ecology and biogeography from
Biogeography and Evolution in New Zealand.

As discussed, at least one architect of the Modern Synthesis supported the
idea of ecological speciation (Huxley (1942). Nevertheless, Mayr (1942) and
recent authors have pointed out fundamental problems with this model. In
parallel development, the traditional idea that ecological factors
determine the geographic distribution of groups has been contradicted by
recent work on species distribution models, and this is discussed here.

What, then, is the exact significance of ecology in determining
distribution? Some of the most obvious spatial patterns in biology can be
explained by more or less obvious ecological factors. For example, bands of
particular species occur at different heights along the seashore or on a
mountain range. But  do ecological factors also determine a group’s
geographic distribution?

Ecology and biogeography both investigate biological differentiation in
space and time, and the only real difference is the scale at which this is
studies. For example, consider the biogeographic region cited earlier, an
area of hill forest comprising a center of endemism 50km across.
Distribution at this large scale involves endemic species and phylogenetic
factors; outside the region, equivalent habitats include different species.
Within the area of endemism, species will occur in suitable habitats, for
example, in lowland or montane sites, by streamsides or on ridges.
Distribution at this medium scale is determined by ecology. At the smallest
scales, stochastic factors can determine whether a tree is found at a
certain spot or, say, a few centimeters to the left.

Ecological factors can eliminate a group from a site, but they do not
determine which groups are in the region to begin with. At the regional
scale, New Zealand is significant not just for its endemics but also for
the groups that are absent, despite the presence of suitable habitat there.
For example, it is one of the few areas in the world where the aquatic
plant *Ceratophyllum* (Ceratophyllaceae) is not indigenous, despite the
fact that it has been introduced to New Zealand and is now a week there.
Why was *Ceratophyllum *(along with many others) absent to start with,
before anthropogenic change took place? The pattern cannot be explained by
ecology. The same is true for New Zealand endemics that become weeds
elsewhere, such as two of the three stick insect species in Britain (Lee,
1999), and the freshwater snail *Potamopyrgus antipodarum,* which now
reaches very high densities in many parts of the United States. Ecological
and physiological factors explain why introduced *Ceratophyllum* survives
in New Zealand and why the former New Zealand endemics now thrive overseas,
but they do not explain the original distributions of the groups.

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