Effects of elevated atmospheric CO2 and/or O3 on intra- and interspecific competitive ability of aspen.

Three model communities of trembling aspen (monoculture, and mixed with either paper birch or sugar maple) were grown for seven years in elevated atmospheric CO(2) and O(3) using Free Air CO(2) Enrichment (FACE) technology. We utilized trends in species' importance, calculated as an index of volume growth and survival, as indications of shifting community composition. For the pure aspen communities, different clones emerged as having the highest change in relative importance values depending on the pollutant exposure. In the control and elevated CO(2) treatments, clone 42E was rapidly becoming the most successful clone while under elevated O(3), clone 8 L emerged as the dominant clone. In fact, growth of clone 8 L was greater in the elevated O(3) treatment compared to controls. For the mixed aspen-birch community, importance of aspen and birch changed by - 16 % and + 62 %, respectively, in the controls. In the treatments, however, importance of aspen and birch changed by - 27 % and + 87 %, respectively, in elevated O(3), and by - 10 % and + 45 %, respectively, in elevated CO(2). Thus, the presence of elevated O(3) hastened conversion of stands to paper birch, whereas the presence of elevated CO(2) delayed it. Relative importance of aspen and maple changed by - 2 % and + 3 %, respectively, after seven years in the control treatments. But in elevated O(3), relative importance of aspen and maple changed by - 2 % and + 5 %, respectively, and in elevated CO(2) by + 9 and - 20 %, respectively. Thus, elevated O(3) slightly increases the rate of conversion of aspen stands to sugar maple, but maple is placed at a competitive disadvantage to aspen under elevated CO(2).

Signals and behavioural responses are not coupled in males: aggression affected by replacement of an evolutionarily lost colour signal.

Male Sceloporus virgatus lack the blue abdominal patches which are used during aggressive encounters in other Sceloporus lizards. Herein we report that, despite having lost this signal, males have retained a behavioural response to experimentally restored blue abdominal patches. We tested two adaptive hypotheses: selection acted primarily upon signallers or selection acted upon both signallers and receivers. The first predicts that only the signal is lost and that male interactions should be affected by the restoration of blue patches. The latter predicts that both the signal and behavioural response are lost and the display of the restored blue patches should have no effect on male-male interactions. We compared the behaviour of receivers in paired encounters where one male (signaller) had blue-painted abdominal patches to a set of trials where both males had white-painted abdomens, unmanipulated abdomens or a novel-painted pattern. The receivers of the blue-painted signal were more likely to display submissive behaviour. The receivers in either the unmanipulated, white-painted or novel-painted signal trials were more likely to display neutral behaviour. These results support the hypothesis that receivers have retained a behavioural response and selection has acted primarily on the signaller. We believe this is the first documentation of males responding to an evolutionarily lost signal in conspecific males.