Influence of sampling strategy on the relationships between fauna and vegetation structure,plant lifeform and floristics

The effect of sampling strategy on animal-habitat relationships was evaluated with data collected from a 50 ha area containing a sequence of tropical vegetation types. Sampling sites were located randomly within defined habitat types (i.e. stratified random sampling) and systematically irrespective of habitat type. At each site the fauna, comprising birds (63 species), reptiles (15 species), amphibia (13 species) and grasshoppers (32 species) were sampled for the abundance of species. Simultaneously, vegetation and related data, comprising vertical structure (52 attributes), ground surface condition (18 attributes), plant lifeform (18 attributes) and the abundance of plant species (200) were recorded. Random and systematic data matrices, comprising sites defined by animal or vegetation attributes, were reduced dimensionally by correspondence analysis. Animal first dimension vectors were then regressed on the first dimension vectors of vegetation structure, lifeform and floristics, respectively. With stratified random sampling, vegetation structure (comprising vertical and ground attributes) and lifeform explained most of the variation in the fauna; floristics were not a significant factor. On the other hand with the systematic data, fioristics explained almost all of the variation in animal abundance and distribution. By removing the ecotonal sites from the systematic data set and recalculating vectors, the animal—vegetation relationships became similar to those generated from the stratified random sampling data. Clearly, the sampling strategy employed in a faunal survey has a major influence on the inventory of species, and on the relative importance of vegetation structure, lifeform and floristics in explaining animal distribution. The presence of ecotones in the systematic data set was highlighted as the key to the difference between the sampling strategies.     

Use of Bullfrog Tadpoles (Rana catesbeiana) to Examine the Mechanisms of Lead Neurotoxicity

Sublethal exposure to lead elicits changes in behavior, particularlylearning. Previously, we had shown that bullfrog tadpoles exposedto 1 mg Pb/liter for 7 days exhibit learning deficits in a discriminateavoidance learning assay. The precise mechanisms involved inthese lead-induced learning deficits are not understood, butCNS monoamine neurotransmitter systems have been implicatedin the learning process. In the present study, we exposed bullfrogtadpoles to 1.7± 0.2 mg Pb/liter for 7 days and thencompared concentrations of neurotransmitters from whole brainsamples with those of controls. Serotonin or 5-hydroxytryptamine(5-HT) was significantly decreased in the lead exposed groupwhile the serotonin metabolite, 5-hydroxyindoleacetic acid,(5-HIAA) was similar to controls. No changes were observed inthe catecholamines epinephrine and norepinephijine followinglead exposure. The ratio of 5-HIAA/5-HT was significantly increasedin lead exposed animals as a result of the decrease in 5-HT,suggesting a decrease in 5-HT biosynthesis rather than an increasein 5-HT metabolism. These findings are the first to suggestthat lead exposure in bullfrog tadpoles affects the monoamineneurotransmitters that are implicated in the learning process.The results of the present study, in conjunction with previousevidence of learning deficits following lead exposure, offerthe possibility of correlating lead exposure with learning deficitsand alterations in CNS neurotransmitters in bullfrog tadpoles.The use of this tadpole model shows promise as a means to examineand understand the mechanisms involved in lead neurotoxicity.     

Landscape structure influences tree density patterns in fragmented woodlands in semi‐arid eastern Australia

Landscape and local‐scale influences are important drivers of plant community structure. However, their relative contribution and the degree to which they interact remain unclear. We quantified the extent to which landscape structure, within‐patch habitat and their confounding effects determine post‐clearing tree densities and composition in agricultural landscapes in eastern subtropical Australia. Landscape structure (incorporating habitat fragmentation and loss) and within‐patch (site) features were quantified for 60 remnant patches of Eucalyptus populnea (Myrtaceae) woodland. Tree density and species for three ecological maturity classes (regeneration, early maturity, late maturity) and local site features were assessed in one 100 × 10 m plot per patch. All but one landscape characteristic was determined within a 1.3‐km radius of plots; Euclidean nearest neighbour distance was measured inside a 5‐km radius. Variation in tree density and composition for each maturity class was partitioned into independent landscape, independent site and joint effects of landscape and site features using redundancy analysis. Independent site effects explained more variation in regeneration density and composition than pure landscape effects; significant predictors were the proportion of early and late maturity trees at a site, rainfall and the associated interaction. Conversely, landscape structure explained greater variation in early and late maturity tree density and composition than site predictors. Area of remnant native vegetation within a landscape and patch characteristics (area, shape, edge contrast) were significant predictors of early maturity tree density. However, 31% of the explained variation in early mature tree differences represented confounding influences of landscape and local variables. We suggest that within‐patch characteristics are important in influencing semi‐arid woodland tree regeneration. However, independent and confounding effects of landscape structure resulting from previous vegetation clearing may have exerted a greater historical influence on older cohorts and should be accounted for when examining woodland dynamics across a broader range of environments.     

Field resistance in cowpea, Vigna unguiculata to the cowpea moth, Cydia ptychora

Field evaluation of 26 selected cowpea cultivars showed that several of them had good levels of resistance to Cydia ptychora; TVu 946, Adzuki, ‘Vita 5’ and Igbirra were the most resistant. Percentage seed damaged by the larvae was positively correlated with days to 50% flowering (r= 0.39*), days to 50% pod ripening (r= 0.48*) and weight of 100 seeds (r= 0.56**). All four cultivars were early maturing, had semi-determinate or determinate plant types and carried their pods above the leaf canopy. No single morphological character could be related to the degree of seed damage but some association with phenological characteristics was indicated. Earliness, determinacy and uniform pod maturity were important plant characters associated with the expression of field resistance. Even if these characters are not causative, they provide a rational basis for screening of a large germplasm to identify or synthesise materials with greater resistance to this moth.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.