Austral Ecology

G. MKie, Brendan; Pearson, Richard G.; Cranston, Peter S.

doi: 10.1111/j.1442-9993.2005.01408.xpmid: N/A

Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species‐level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current‐day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna.

Flores, Augusto A. V.; Abrantes, Katya G.; Paula, José

doi: 10.1111/j.1442-9993.2005.01409.xpmid: N/A

Abstract The bubble crab Dotilla fenestrata forms very dense populations on the sand flats of the eastern coast of Inhaca Island, Mozambique, making it an interesting biological model to examine spatial distribution patterns and test the relative efficiency of common sampling methods. Due to its apparent ecological importance within the sandy intertidal community, understanding the factors ruling the dynamics of Dotilla populations is also a key issue. In this study, different techniques of estimating crab density are described, and the trends of spatial distribution of the different population categories are shown. The studied populations are arranged in discrete patches located at the well‐drained crests of nearly parallel mega sand ripples. For a given sample size, there was an obvious gain in precision by using a stratified random sampling technique, considering discrete patches as strata, compared to the simple random design. Density average and variance differed considerably among patches since juveniles and ovigerous females were found clumped, with higher densities at the lower and upper shore levels, respectively. Burrow counting was found to be an adequate method for large‐scale sampling, although consistently underestimating actual crab density by nearly half. Regression analyses suggested that crabs smaller than 2.9 mm carapace width tend to be undetected in visual burrow counts. A visual survey of sampling plots over several patches of a large Dotilla population showed that crab density varied in an interesting oscillating pattern, apparently following the topography of the sand flat. Patches extending to the lower shore contained higher densities than those mostly covering the higher shore. Within‐patch density variability also pointed to the same trend, but the density increment towards the lowest shore level varied greatly among the patches compared.

Letnic, M.; Dickman, C. R.

doi: 10.1111/j.1442-9993.2004.01410.xpmid: N/A

Abstract Patch‐burning is frequently advocated as a management tool to enhance the biodiversity and pasture values of spinifex (Triodia) grasslands. In this study we compare the capture rates of small mammals in habitats regenerating shortly after fire (aged 1–5 years) and in long‐unburnt habitats (aged >25 years). To unravel the effects of temporally and spatially variable rainfall on capture rates, the study was replicated at three locations spaced over 50 km apart that experience different rainfall regimes. Ten species of small mammals were captured over the course of the study, between October 1999 and June 2001. Pseudomys desertor showed a strong preference for long‐unburnt habitats. Notomys alexis, Sminthopsis youngsoni and Sminthopsis hirtipes showed some preferences for regenerating habitats, but these were not consistent throughout the study. Factors indicative of temporal and spatial variation in rainfall, time and site had important effects on capture rates. High rainfalls associated with the La Niña phase of the El Niño/Southern Oscillation in 2000 increased seed production and prompted eruptions of rodent species and the carnivorous Dasycercus cristicauda. The greatest numbers of captures were made at the sites that received the highest rainfalls. We conclude that patch‐burning regimes do not benefit small mammals directly, but are likely to increase the resilience of ‘fire‐sensitive’ species that are dependent on dense spinifex by reducing the extent of wildfires.

Kelaher, Brendan P.

doi: 10.1046/j.1442-9993.2004.01420.xpmid: N/A

Abstract The potential of colonization to contribute to the spatial patterns of six common invertebrates in coralline algal turf was investigated on a rocky shore near Sydney, Australia. The species, which included two amphipods (Elasmopus warra, Hyale spp.), a small bivalve (Lasaea australis), a fly larva (Limonia marina), and two microgastropods (Amphithalamus incidata and Eatoniella atropurpurea), had a range of dispersal modes (larval dispersal, crawling, swimming, rafting, and passive transport). Field sampling between May 1997 and November 1999 demonstrated that the amphipods were more abundant in low‐shore areas, the fly larvae and bivalves were more abundant in mid‐shore areas, and the abundances of gastropods did not vary with tidal height. Furthermore, abundances of all species varied among patches separated by tens of metres at one time or another. To test whether rates of colonization could contribute to established patterns of abundance, habitat mimics were deployed for 2‐week periods. The supply of new individuals matched long‐term patterns of abundance at different tidal heights for E. warra and L. marina. Colonization rates also differed among patches separated by tens of metres for three of the six species. Overall, there was little evidence to suggest that common species in coralline turf are limited by colonization on local scales, regardless of their major mode of dispersal. However, the potential for colonization to determine patterns of abundance varied from species to species.

Vila‐Aiub, Martin M.; Gundel, Pedro E.; Ghersa, Claudio M.

doi: 10.1111/j.1442-9993.2005.01423.xpmid: N/A

Abstract Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non‐competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.

Motta, Rosinês L.; Uieda, Virginia S.

doi: 10.1111/j.1442-9993.2005.01424.xpmid: N/A

Abstract This study investigated the structure and properties of a tropical stream food web in a small spatial scale, characterizing its planktonic, epiphytic and benthic compartments. The study was carried out in the Potreirinho Creek, a second‐order stream located in the south‐east of Brazil. Some attributes of the three subwebs and of the conglomerate food web, composed by the trophic links of the three compartments plus the fish species, were determined. Among compartments, the food webs showed considerable variation in structure. The epiphytic food web was consistently more complex than the planktonic and benthic webs. The values of number of species, number of links and maximum food chain length were significantly higher in the epiphytic compartment than in the other two. Otherwise, the connectance was significantly lower in epiphyton. The significant differences of most food web parameters were determined by the increase in the number of trophic species, represented mainly by basal and intermediate species. High species richness, detritus‐based system and high degree of omnivory characterized the stream food web studied. The aquatic macrophytes probably provide a substratum more stable and structurally complex than the sediment. We suggest that the greater species richness and trophic complexity in the epiphytic subweb might be due to the higher degree of habitat complexity supported by macrophyte substrate. Despite differences observed in the structure of the three subwebs, they are highly connected by trophic interactions, mainly by fishes. The high degree of fish omnivory associated with their movements at different spatial scales suggests that these animals have a significant role in the food web dynamic of Potreirinho Creek. This interface between macrophytes and the interconnections resultant from fish foraging, diluted the compartmentalization of the Potreirinho food web.

Verrier, Frances J.; Kirkpatrick, J. B.

doi: 10.1111/j.1442-9993.2004.01425.xpmid: N/A

Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction.

Williams, Paul R.; Congdon, Robert A.; Grice, Anthony C.; Clarke, Peter J.

doi: 10.1111/j.1442-9993.2004.01426.xpmid: N/A

Abstract The germinable soil seed bank of a tropical eucalypt savanna of north‐eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire‐related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta, Pycnospora lutescens and Triumfetta rhomboidea. Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus. The germinable soil seed bank varied seasonally, increasing from the mid wet season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.

Pollmann, William

doi: 10.1046/j.1442-9993.2004.01427.xpmid: N/A

Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade‐intolerant Nothofagus are likely not to survive in competition with shade‐tolerant, broad‐leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse‐scale disturbance. Comparison of stand dynamics of three old‐growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade‐offs of this variation were made. Stem density of all stems ≥5.0 cm d.b.h. was 233–303 stems per hectare, and basal area was 123.9–171.0 m2ha−1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long‐term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over‐ and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid‐tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small‐to‐intermediate‐sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long‐term.

Cunningham, Saul A.; Floyd, Robert B.; Weir, Tom A.

doi: 10.1111/j.1442-9993.2005.01429.xpmid: N/A

Abstract We examined the potential of forest plantations to support communities of forest‐using insects when planted into an area with greatly reduced native forest cover. We surveyed the insect fauna of Eucalyptus globulus (Myrtaceae) plantations and native Eucalyptus marginata dominated remnant woodland in south‐western Australia, comparing edge to interior habitats, and plantations surrounded by a pastoral matrix to plantations adjacent to native remnants. We also surveyed insects in open pasture. Analyses focused on three major insect orders: Coleoptera, Lepidoptera and Hymenoptera. Plantations were found to support many forest‐using insect species, but the fauna had an overall composition that was distinct from the remnant forest. The pasture fauna had more in common with plantations than forest remnants. Insect communities of plantations were different from native forest both because fewer insect species were present, and because they had a few more abundant insect species. Some of the dominant species in plantations were known forestry pests. One pest species (Gonipterus scutellatus) was also very abundant in remnant forest, although it was only recently first recorded in Western Australia. It may be that plantation forestry provided an ecological bridge that facilitated invasion of the native forest by this nonendemic pest species. Plantation communities had more leaf‐feeding moths and beetles than remnant forests. Plantations also had fewer ants, bees, evanioid wasps and predatory canopy beetles than remnants, but predatory beetles were more common in the understory of plantations than remnants. Use of broad spectrum insecticides in plantations might limit the ability of these natural enemies to regulate herbivore populations. There were only weak indications of differences in composition of the fauna at habitat edges and no consistent differences between the fauna of plantations adjacent to remnant vegetation and those surrounded by agriculture, suggesting that there is little scope for managing biodiversity outcomes by choosing different edge to interior ratios or by locating plantations near or far from remnants.