Timing is everything? Phenological synchrony and population variability in leaf‐chewing herbivores of Quercus

Abstract.  1. Specialization on ephemeral resources (e.g. new leaves) should produce large annual variation in herbivore population size when the timing of availability of those resources is unpredictable. Despite considerable evidence for impacts of synchrony with budburst on survival of larval Lepidoptera, previous studies of adult Geometridae and Noctuidae found no correlations between insect phenology and population variability.
2. We surveyed larval Lepidoptera feeding on Quercus alba and Q. velutina in Missouri from 1993 to 2003 and examined population variability, measured as the coefficient of variation of population density (CV), in a subset of abundant species. We compared CV values among species whose larvae feed only in spring, early summer, mid-summer, late summer, or all season. We predicted that univoltine species whose larvae eclose and complete development in spring during leaf expansion would have higher variability than species feeding later in the season, having multiple generations, or having longer development times.
3. As predicted and consistent with hypotheses, spring-feeding species had CV values 32% higher than species feeding in summer months. Coefficients of variation were also 34% higher in leaf-rolling and mining guilds compared with free-feeders, suggesting that mobile species may compensate for asynchrony with budburst by dispersing to higher quality plants or plant parts. Multivoltine species, however, did not differ from univoltine species in population variability.
4. Our results suggest that asynchrony with plant phenology and factors that might exacerbate it, such as climate change, will have the largest impacts on the dynamics of spring-feeding Lepidoptera, particularly species with limited mobility.     

The Influence of Volatile Substances from Incubated Litter of Pinus radiata on Seed Germination

Vapour from incubated Pinus radiata D. Don litter caused a depressionin the germination of Lolium perenne L. seeds and responsesvarying from stimulation to depression in germination of Trifoliumrepens L. seeds. These effects could be attributed to ethyleneand carbon dioxide. Experiments using ethylene and carbon dioxidesupported this conclusion. Pinus radiata, litter, Lolium perenne, Trifolium repens, seed germination, ethylene, carbon dioxide     

Temporal variation in bird assemblages: How representative is a one‐year snapshot?

Abstract Bird assemblages generally are no longer regarded as stable entities, but rather as fluctuating in response to many factors. Australia's highly variable climate is likely to result in a high degree of dynamism in its bird assemblages, yet few studies have investigated variation on an inter‐annual temporal scale. We compared 2 year‐long samples of the bird assemblages of a series of highly fragmented buloke Allocasuarina luehmannii (Casuarinaceae) woodland remnants in south‐eastern Australia, the first sample taken in 1994–95 and the second in 2001–02. Bird densities were almost three times higher in the second period than in the first. Mean species richness also was significantly higher. Species richness of each individual site was unrelated between the 2 years. Minimum species turnover was 63% and was higher, on average, for migratory and nomadic than for sedentary species. Therefore, site‐level bird assemblage composition was markedly different between the two survey periods and, on average, the assemblage composition of each site bore greater resemblance to those of other sites in the same year than to that of the same site in the other survey period. Most species changed substantially in their distribution among remnants between the two periods. The change in distribution of most species did not differ significantly from that expected if the species had redistributed at random among the sites. This suggests that although the remnant vegetation of the area is highly fragmented with minimal interpatch connectivity, bird movements among remnants are relatively frequent. Inter‐annual variability in Australian bird assemblages may be higher than is commonly recognized. In such dynamic systems, we must be cautious when extrapolating from the findings of short‐term studies to longer temporal scales, especially in relation to conservation management. A greater understanding of the processes driving distributional patterns is likely to enable better predictions of species’ responses to habitat change.     

Fruit removal of Coprosma quadrifida (Rubiaceae) by birds in south-eastern Australia

Abstract Removal of the fleshy fruits of Coprosma quadrifida by birds was examined in relation to fruit crop size, neighbouring fruit crop size and time in the season in montane wet sclerophyll forest in south-eastern Australia. On average, 84% of individual fruit crops were removed. Frugivores removed fruit in proportion to its abundance, indicating that they continually assess availability rather than respond to a critical abundance. The size of neighbouring fruit crops did not influence fruit removal rates, suggesting that there is little competition among neighbours for dispersers. The ripe fruits of C. quadrifida were eaten by 14 bird species, comprising 50% of the bird species trapped. Silvereyes (Zosterops lateralis) were the most abundant consumers of fruits. With the exception of the parrot, Platycercus elegans, all birds defecated seeds intact and had no influence on seed viability.     

Shelf-life of stored asparagus is strongly related to post-harvest accumulated heat units

The effect of delay between harvest and hydrocooling, and of regimes of simulated air transport temperatures, on shelf-life of fresh asparagus were quantified. Shelf-life was strongly negatively correlated with the accumulated heat units experienced between harvest and post-transport handling. A 2-h delay in hydrocooling after harvest was similar to a 0.5°C higher temperature during a 2-day transit period in effect on shelf-life. It is essential for maximum shelf-life that asparagus be kept cold from the completion of hydrocooling until sale.     

Cascading effects of host size and host plant species on parasitoid resource allocation

1. The bottom‐up factors that determine parasitoid host use are an important area of research in insect ecology. Host size is likely to be a primary cue for foraging parasitoids due to its potential influence on offspring development time, the risk of multiparasitism, and host immunocompetence. Host size is mediated in part by host‐plant traits that influence herbivore growth and potentially affect a herbivore's quality as a host for parasitoids. 2. Here, we tested how caterpillar host size and host plant species influence adult fly parasitoid size and whether host size influences wasp parasitoid sex allocation. We measured the hind tibia lengths and determined the sex of wasp and fly parasitoids reared from 11 common host species of polyphagous caterpillars (Limacodidae) that were in turn reared on foliage of seven different host plant species. 3. We also tested how host caterpillar species, host caterpillar size, and host and parasitoid phenology affect how the parasitoid community partitions host resources. We found evidence that parasitoids primarily partition their shared hosts based on size, but not by host species or phenology. One index of specialisation (d′) supports our observation that these parasitoids are quite generalised within the Limacodidae. In general, wasps were reared from caterpillars collected in early instars, while flies were reared from caterpillars collected in late instars. Furthermore, for at least one species of solitary wasp, host size influenced sex allocation of offspring by ovipositing females. 4. Host‐plant quality indirectly affected the size attained by a tachinid fly parasitoid through its direct effects on the size and performance of the caterpillar host. The host plants that resulted in the highest caterpillar host performance in the absence of enemies also yielded the largest parasitoid flies, which suggests that host plant quality can cascade up to influence the third trophic level.