A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76–84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

The Macarthur-Bates Communicative Development Inventories (CDI) have been used widely to document early communicative development. The paper reports on a large community sample of 1,447 children recruited from low, middle and high socioeconomic (SES) areas across metropolitan Melbourne, Australia. Regression analyses were conducted to determine the extent to which communicative behaviours reported at 0 ; 8 and 1 ; 0 predicted vocabulary development at 1 ; 0 and 2 ; 0. In support of previous findings with smaller, often less representative samples, gesture and object use at 1 ; 0 were better predictors of 2 ; 0 vocabulary than were gesture and object use at 0 ; 8. At 1 ; 0, children from the lower SES groups were reported to understand more words than children from the higher SES groups, but there were no SES differences for words produced at 1 ; 0 or 2 ; 0. The findings add to our understanding of the variability in the development of early communicative behaviours.

Three 5-HT receptors have been implicated in retinal processing but positive identification of the receptors and the localization of receptor subtypes in the retina have not been achieved. In this study, molecular techniques were used to identify one class of 5-HT receptor—5-HT2a—in the retina, and immunohistochemical techniques were used to localize the receptor in the retinal network. Reverse transcription polymerase chain reaction (RT-PCR) techniques were used to identify a segment of the rabbit 5-HT2a gene; a 422 base fragment was identified, cloned, and sequenced. The fragment shows a high degree (ca. 90%) of nucleotide sequence identity with the 5-HT2a receptor gene from other mammals. 5-HT2a immunoreactivity was seen in both the inner and outer plexiform (synaptic) layers of the retina. Using cell-type-specific markers, the 5-HT2a immunoreactivity was shown to be on the terminals of photoreceptor and rod bipolar cells. This association of 5-HT2a receptors with these two synapses suggests that serotonin may be a modulator of synaptic function in the retina.