|Images from Google Earth highlight just how much |
woodland clearing has occurred
in western Victoria for cropping and grazing
In our Lab, we've been testing the idea that small populations are more vulnerable to local extinction than large populations. Despite the simplicity of the hypothesis, there is not a lot of good evidence around in the literature to support or reject this idea (at least for plants in Australian ecosystems).
To address this question, we've employed re-visitation studies. This involves using data on species abundance collected at some previous point in time from well-defined places (lets call this the historical dataset, time1), and revisiting the very same places some time later to determine whether species have persisted (lets call this the contemporary dataset, time2). If you have data on abundance at t1, you can start to understand whether the smallest populations at this time are less likely to be present at t2 (as theory would suggest).
We used data collected in 1975 by a superb amateur botanist called Cliff Beauglehole as our t1 for a number of remnant grasslands and grassy woodlands in western Victoria.
|Scaly Buttons is one of the common species|
in grasslands and woodlands that has declined
over the last three decades
(Photo: John Morgan)
Beuglehole recorded species lists for these sites (many of which were very diverse at the time) and allocated an 'abundance' measure for each species at each site that approximates a log scale - a few dozen, up to 100, in the 100s, in the 1000s.
We re-visited these same sites (t2) and recorded all species we could find; importantly, we estimated their population size in the same way as Beuglehole. When comparing the data on abundance at t1 versus t2, remembering that small populations should be more vulnerable to local extinction, we found some very interesting results which we have reported in the Journal of Ecology.
|Changes in population abundances of native plants species |
from 1975 to 2006 in grassy woodlands in western Victoria
(From: Sutton & Morgan Journal of Ecology)