Microfossils and evidence of land plant evolution

Resolving the question of (1) land plant and (2) vascular land plant evolution is a complex problem. It requires a continued, multidisciplinary effort. We are all grateful to Dianne Edwards and her colleagues (Edwards et al. 1979) for pursuing one such line of research with careful attention to morphology and stratigraphy. Their efforts, however, are confined to one small part of the globe, and they perforce involve only one type of evidence effective with regard to questions of vascular plant evolution once the land estate has been reached. They do not deal with the basic question of vascular and non-vascular land plant origins. The so-called Přídolí benchmark that remained the sine qua nun for vascular plant evolution when Dianne Edwards began her studies has now been irrevocably breached. What other supposedly sacrosanct benchmarks will also crumble as the result of future discoveries, now that vascular plants have been recovered from lower Ludlovian strata? Nevertheless, pre-Devonian plant megafossils are too rare to yield definitive results with regard to the origin of land plants prior to the vascular estate, even though they could in principle (as emphasized by Edwards et al. 1979) provide the least ambiguous evidence. We must look elsewhere than to megafossils for evidence suggesting links in time between green algal ancestors, major groups of living green land Plants, and the many extinct groups of enigmatic higher land plants in the crucial Early Paleozoic time interval.     

Interspecific competition in Drosophila II. Competitive outcome in some 2–resource environments

Populations of Drosophila metanogaster and D. simulans were made to compete in a number of 2– resource environments. The resources used were all based on a standard Drosophila medium and differed from each other only in their concentrations of ethanol. Each experiment comprised three cages started at a species–frequency of 0.8 D. melanogaster and three at 0.2 D. melanogaster. This enabled screening for a wide range of equilibria.
Reversal of competitive superiority was achieved (unintentionally) by raising the alcohol level of one of the resources. Thus while D. simulans won in an environment with media containing 0 and 896 ethanol, D. melanogaster won if the ethanol concentrations were 0 and 10%, or 0 and 12%. This parallels the reversal of dominance reported earlier for single–resource systems. However, in none of the 2–resource systems studied was there a stable equilibrium in species–frequency–in fact there was no significant frequency–dependence at all.
An artificial selection experiment produced a stock of D. melanogaster ovipositing a higher proportion of eggs on the alcoholic resource. Thus, this stock was more divergent from D. simulans , in at least one aspect of resource use, than was the original stock of D. melanogaster. However, competition between stock D. simulans and selected D. melanogaster showed no frequency–dependence. Again, reversal of competitive dominance was unintentionally achieved.
The implications of these results are discussed, and the need for a comprehensive study of resource–utilization in a pair of competing species is stressed.     

Woodland Caribou Extirpation and Anthropogenic Landscape Disturbance in Ontario

Abstract: The decline of woodland caribou (Rangifer tarandus caribou) has been attributed to anthropogenic landscape disturbances, but critical distance thresholds and time lags between disturbance and extirpation are unknown. Using a database of caribou presence and extirpation for northern Ontario, Canada, geo-coded to 10 times 10-km cells, we constructed logistic regression models to predict caribou extirpation based on distance to the nearest of each of 9 disturbance types: forest cutovers, fires, roads, utility corridors, mines, pits and quarries, lakes, trails, and rail lines. We used Akaike's Information Criterion to select parsimonious models and Receiver-Operating Characteristic curves to derive optimal thresholds. To deal with the effects of spatial autocorrelation on estimates of model significance, we used subsampling and restricted randomizations. Forest cutovers were the best predictor of caribou occupancy, with a tolerance threshold of 13 km to nearest cutover and a time lag of 2 decades between disturbance by cutting and caribou extirpation. Management of woodland caribou should incorporate buffers around habitat and requires long-term monitoring of range occupancy.