Landscape partitioning among Triodia spp. (Poaceae) in the fire prone Kimberley,north‐west Australia

The processes which determine the structure of plant communities vary across spatial and temporal scales. Climatic factors are more likely to influence community structure at a regional scale with more transient environmental effects such as disturbance or demographic interactions having a greater influence at local scales. Understanding these differences is important for managing communities at a landscape scale. Triodia spp. grasslands are the most extensive plant community in Australia, covering 1.4 million km², and yet little is known about the processes which structure these communities. We collected data on six sympatric Triodia spp. at the regional, landscape and local scale across the 325 000 ha property, Mornington Wildlife Sanctuary, in the Kimberley region of northern Western Australia to investigate the processes which structure this community. Regionally we looked for correlations between species distributions and substrate or rainfall. At the landscape scale we collected data on substrate, drainage and vegetation type and at the local scale we determined the extent to which individuals form mono‐specific stands both along and across the contour gradient. Only one species, T. aeria, was found to be substrate specific and only T. epactia was restricted to the drier southern end of the property. The other species were not restricted by substrate or rainfall at the regional scale and were found to be habitat generalists at the landscape scale. All species grew in mono‐specific stands with little to no mixing at shared boundaries. However, this pattern broke down when crossing the contour gradient on hillsides. The results suggest rainfall may influence the distribution of some Triodia spp. at a regional scale with interspecific competition, due to differences in post‐fire regeneration niches, structuring the community at the local scale. At the landscape scale community structure appears to be influenced by feedback mechanisms involving differences in the post‐fire regeneration strategies of sympatric species and subsequent competition for establishment microsites.     

Masquerade is associated with polyphagy and larval overwintering in Lepidoptera

Masquerading animals benefit from the difficulty that predators have in differentiating them from the inedible objects, such as twigs, that they resemble. The function of masquerade has been demonstrated, but how it interacts with the life history of organisms has not yet been studied. Here, we report the use of comparative analyses to test hypotheses linking masquerade to life‐history parameters. We constructed a phylogenetic tree of the British species of the lepidoptera families Geometridae and Drepanidae, and compiled life history and coloration data from the literature. We found that masquerade is associated with the exploitation of a greater diversity of host plants whether measured by the number of families or genera. We found a positive relationship between body size and polyphagy among masquerading species, and no relationship among cryptic species. Among those species predominantly found on woody host plants, masquerading species are more likely to overwinter as larvae while cryptic species mostly overwinter as pupae. Polyphenism was associated with multivoltinism in masquerading species but not cryptic species. Taken together, our results show that masquerade must be viewed as a strategy distinct to crypsis and hence may provide insights into the evolution of both defensive strategies. Our study further demonstrates the utility of broad‐scale between‐species comparisons in studying associations between diverse life‐history parameters and sensory aspects of predator‐prey interactions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 90–103.     

Protection by association: evidence for aposematic commensalism

Aposematism is a well known and widely used strategy for reducing predation by conspicuous signalling of unprofitability. However, the increased conspicuousness could make this strategy costly if there are no secondary defences to back the signal up. This has made the elucidation of the evolutionary mechanisms for aposematism and that of the closely‐related Batesian and Mullerian mimicry difficult. The present study aims to test whether cryptic and nondefended prey could reduce their predation risk by grouping with aposematic and defended prey. To do this, we used groups of artificial baits that were either cryptic and palatable or conspicuous and unpalatable, along with the corresponding control treatments. These were then presented in mixed and homogeneous treatment groups within a field setting and the local wild bird assemblage was allowed to select and remove baits at will. The results obtained show that undefended non‐aposematic prey can benefit by grouping with aposematic prey, with no evidence that predation rates for aposematic prey were adversely affected by this association. These results provide insights into the evolution of Batesian mimicry. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 81–89.     

Foraging guild membership explains variation in waterbird responses to the hydrological regime of an arid‐region flood‐pulse river in Namibia

1. Little is known about hydrological influences on tropical waterbird communities. We used a 16‐year data set (1991–2007) of waterbird censuses, together with a classification of observed species into foraging guilds, to explore the relationships between natural variations in flow regime, foraging guild and the community composition of waterbirds at the Okavango River in the Caprivi Strip of north‐eastern Namibia, southern Africa. 2. We addressed three hypotheses to explain variation in waterbird community composition: (i) exploitation (birds move towards resource‐rich patches to exploit periods of high food abundance); (ii) escapism (declines in regional habitat quality force birds to aggregate in perennial waterbodies); and (iii) interaction (bird assemblages are dominated by intra‐ and interspecific interactions, such as flock formation for breeding or moulting, that can be explained better by life history demands or competition than by resource availability). 3. Waterbirds in different foraging guilds responded strongly but at different periods to changes in the hydrological environment, creating a complex but predictable successional pattern in community composition through time. Deep‐water feeders responded fastest (abundance peaking 2 months post‐flood), followed by shallow‐water feeders (4 months) and emergent vegetation feeders (7 months). Species that forage on short vegetation or in mud showed a bimodal response with peaks in abundance at 3 and 8 months post‐flood. 4. Our results indicated a strong effect of the local flow regime and hence supported the exploitation hypothesis. The foraging guild approach allowed us to identify clear patterns in a highly complex ecosystem and shows considerable promise as an analytical tool for similar data sets. Our results further suggest that while the entire bird community will be affected by hydrological alterations such as impoundments, water extraction and climate change, deep‐water feeders may be one of the most vulnerable groups.     

Plasticity in photosynthetic response to nutrient supply of seedlings from a mixed conifer‐angiosperm forest

Abstract We measured the plasticity of the response of photosynthesis to nutrient supply in seedlings of the dominant four conifer and broadleaved angiosperm tree species from an indigenous forest in South‐westland, New Zealand. We hypothesized that the response of conifers to differing nutrient supply would be less than the response for the angiosperms because of greater adaptation to low fertility conditions. In Prumnopitys ferruginea (D. Don) de Laub. the maximum velocity of electron transport, J_max, doubled with a 10‐fold increase in concentration of nitrogen supply. In Dacrydium cupressinum Lamb. the maximum velocity of carboxylation, V_cmax, doubled with a 10‐fold increase in phosphorus supply. In contrast, photosynthetic capacity for the angiosperm species Weinmannia racemosa L.f. was affected only by the interaction of nitrogen and phosphorus and photosynthetic capacity of Metrosideros umbellata Cav. was not affected by nutrient supply. The response of the conifers to increasing availability of nutrient suggests greater plasticity in photosynthetic capacity, a characteristic not generally associated with adaptation to soil infertility, thus invalidating our hypothesis. Our data suggest that photosynthetic response to nutrient supply cannot be broadly generalized between the two functional groups.     

Stay‐green: A consequence of the balance between supply and demand for nitrogen during grain filling?

Retention of green leaf area in grain sorghum under post‐anthesis drought, known as stay‐green, is associated with greater biomass production, lodging resistance and yield. The stay‐green phenomenon can be examined at a cell, leaf, or whole plant level. At a cell level, the retention of chloroplast proteins such as LHCP2, OEC33 and Rubisco until late in senescence has been reported in sorghum containing the KS19 source of stay‐green, indicating that photosynthesis may be maintained for longer during senescence in these genotypes. At a leaf level, longevity of photosynthetic apparatus is intimately related to nitrogen (N) status. At a whole plant level, stay‐green can be viewed as a consequence of the balance between N demand by the grain and N supply during grain filling. To examine some of these concepts, nine hybrids varying in the B35 and KS19 sources of stay‐green were grown under a post‐anthesis water deficit. Genotypic variation in delayed onset and reduced rate of leaf senescence were explained by differences in specific leaf nitrogen (SLN) and N uptake during grain filling. Matching N supply from age‐related senescence and N uptake during grain filling with grain N demand found that the shortfall in N supply for grain filling was greater in the senescent than stay‐green hybrids, resulting in more accelerated leaf senescence in the former. We hypothesise that increased N uptake by stay‐green hybrids is a result of greater biomass accumulation during grain filling in response to increased sink demand (higher grain numbers) which, in turn, is the result of increased radiation use efficiency and transpiration efficiency due to higher SLN. Delayed leaf senescence resulting from higher SLN should, in turn, allow more carbon and nitrogen to be allocated to the roots of stay‐green hybrids during grain filling, thereby maintaining a greater capacity to extract N from the soil compared with senescent hybrids.     

The evolution and ecology of masquerade

Many organisms appear to mimic inanimate objects such as twigs, leaves, stones, and bird droppings. Such adaptations are considered to have evolved because their bearers are misidentified as either inedible objects by their predators, or as innocuous objects by their prey. In the past, this phenomenon has been classified by some as Batesian mimicry and by others as crypsis, but now is considered to be conceptually different from both, and has been termed ‘masquerade’. Despite the debate over how to classify masquerade, this phenomenon has received little attention from evolutionary biologists. Here, we discuss the limited empirical evidence supporting the idea that masquerade functions to cause misidentification of organisms, provide a testable definition of masquerade, and suggest how masquerade evolved and under what ecological conditions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 1–8.     

A Response Surface Analysis of the Effects of Cyclohexanecarboxylic Acid and 2,4-Dichlorophenoxy Acetic Acid on Nitrogen Metabolism in Phaseolus vulgaris L.

Primary leaves of 2-week-old bush bean plants (Phaseolus vulgariscv ‘Top Crop’) were treated with one of 36 combinationsof cyclohexanecarboxylic acid (CHCA) and 2,4-dichlorophenoxyacetic acid (2,4-D), each at six equally spaced concentrationsFive, 7, 9 and 11 days after treatment, one plant from eachcombination was harvested, and primary leaves were monitoredfor nitrate reductase activity (NRA), nitrate nitrogen (N) concentration,organic N concentration, and d wt NRA was assayed by an in vivoprocedure Data from the resulting 6 x 6 x 4 factorial configuration foreach of the four responses were analysed using the method oforthogonal polynomials, which is described in detail This method,based on equally spaced levels, produced independent polynomialexpressions in CHCA concentration, 2,4-D concentration, and/ortime-to-harvest after treatment, which were then fitted to thedata on each response by simple linear regression analyses.A graphical procedure was used to compare predicted responsesfrom the best fit equations with the actual data. Examination of computer-generated plots of the three-dimensionalresponse surfaces revealed that NRA, organic N concentration,and d wt decreased with increasing 2,4-D concentration, whereasnitrate N content increased Increasing CHCA concentration generallyhad the opposite effect on NRA and nitrate N content, althoughinteraction between the two chemicals was evident in the latterresponse Organic N content remained unchanged as CHCA concentrationincreased, while d wt first increased then decreased Possibleexplanations for these results are discussed, as are the advantagesof using factorial designs with equally-spaced levels in plantgrowth studies. Phaseolus vulgaris L, bush bean, nitrogen metabolism, plant growth regulators, cyclohexanecarboxylic acid, 2,4-dichlorophenoxy acetic acid, regression analysis, orthogonal polynomials, response surfaces analysis     

The abundance of ground-dwelling invertebrates in a Victorian forest affected by ‘dieback’(Phytophthora cinnamomi) disease

Abstract Phytophthora cinnamomi (cinnamon fungus) is a pathogenic soil fungus that infects plant communities along the southeastern coast of Australia and the southwestern corner of Western Australia. Infection of native plant communities with P. cinnamomi regularly leads to dramatic changes in both the structural and the floristic characteristics of these communities. This study aimed to assess the effect of P. cinnamomi induced changes in plant community attributes upon the abundance and diversity of invertebrates in an area of open forest in the Brisbane Ranges, Victoria. Pitfall trapping was conducted continuously for 1 week within each season over a 3 year period. Invertebrates were sorted to order level, and abundances were compared between times (season and year) and infection status for taxa with normalized distributions (Coleoptera, Collembola, Dermaptera and ants). Non-parametric comparisons were made for other groups (Aranae, Blattodea, Diptera, Hemiptera, Orthoptera, ant ‘morpho-species’ and unidentified larvae) to assess differences on the basis of infection status. Significant differences on the basis of infection were uncommon and, where identified, elevated abundances were more commonly observed at sites infected by P. cinnamomi. Consistent temporal effects (season and year) were observed in normalized data sets. Abundances both within individual taxa and from pooled counts were generally weakly associated with ground-level habitat features. Overall, the impact of P. cinnamomi on vegetative structure and floristics was not reflected in different abundances of ground-dwelling invertebrates.