Forest‐fire regimes affect thermoregulatory opportunities for terrestrial ectotherms

Fire‐induced changes in canopy openness may affect sunlight penetration to the forest floor, and thus the operative temperatures available to terrestrial ectotherms. We examined thermal regimes for two types of ectotherms: diurnally active species that utilize sun‐exposed patches to regulate their body temperatures, and nocturnally active species that depend upon solar radiation striking the rocks under which they shelter. We measured canopy openness, shrub height, radiation transmission and operative environmental temperatures in the open and inside reptile retreat‐sites, at 24 study sites in eucalypt forests in two regions (Gosford and Yengo) in south‐eastern Australia. All sites were last burnt in 2000–2001, but had experienced different fire frequencies (1–4 fires over the previous 37 years). In Gosford, higher fire frequencies reduced canopy openness and radiation transmission at ground and shrub level, and thus reduced environmental temperatures and the thermal quality of reptile habitats. Our modelling based on thermal preferenda of an endangered snake species (the broad‐headed snake Hoplocephalus bungaroides) suggests that increased fire frequency at Gosford halved the amount of time an animal could spend within its preferred (set‐point) range, regardless of whether it thermoregulated beneath rocks or basked out in the open. At Yengo, however, fire frequency did not affect the thermal quality of reptile habitats. Thus, the effects of fire frequency on forest structure and the thermal environment at ground level differed between adjacent areas, and relatively small changes in canopy openness translated into major effects on thermoregulatory opportunities for reptiles. Although fire is a useful management tool for creating open habitats, we need to understand more about the effects of fire frequency on vegetation structure and thermal environment before we can use fire to manage habitats for reptiles.     

Nest‐site selection by crocodiles at a rocky site in the Australian tropics: Making the best of a bad lot

Most animals select nest sites non‐randomly, reflecting benefits of specific locations or incubation conditions for offspring viability as well as risks or costs to the reproducing adult. If few or no available nest sites offer suitable conditions, we expect animals to make the best of a bad lot, by selecting nest sites that provide the best conditions available. In tropical north‐western Australia, freshwater crocodiles (Crocodylus johnstoni: Crocodylidae) in a large artificial lake (Lake Argyle) experience this challenge: the types of nest sites used by this species in other parts of its range (moist, shaded sandy soils, far from the water's edge) are scarce. Measurements of 89 crocodile nests and 89 test holes (abandoned attempts at nesting) at Lake Argyle, and 28 nests on the nearby Ord River, show that most areas along the lakeshore are too steep and rocky for nesting. Crocodiles at the lake therefore are forced to nest at sites that are sun‐exposed, in dry gravelly substrates, and close to the water's edge. Comparisons of test holes and actual nests within such areas show that nesting crocodiles actively select sites that are less rocky, are suitable hydrically, and that provide stable thermal regimes. Those hydric and thermal attributes allow successful development of the offspring. The ability of freshwater crocodiles in Lake Argyle to flexibly modify their nest‐site selection criteria, under severe constraints enforced by this open rocky landscape, are critical to the species' success in exploiting the opportunity created by the dam's construction.     

Importance of matrix permeability and quantity of core habitat for persistence of a threatened saltmarsh bird

Species habitat preferences can be obscured when individuals have been recorded in non‐core habitats because of dispersal, spillover effects or spatial errors in observation locations. Disentangling the direct effects of the habitats species are observed in from the effects of proximity to other nearby habitats is especially challenging in fragmented landscapes, as many fragmentation metrics are correlated and it is difficult to prove independent effects. In this paper we addressed this issue by comparing a number of models based on predefined ecological theories. We compared models based on quantity of core habitat surrounding observations, proximity to core habitat, or a combination of the two to explain the observed distribution of the saltmarsh inhabiting white‐fronted chat (Epthianura albifrons) in coastal New South Wales, Australia. Proximity to core habitat was considered as either Euclidean distance or cost distance, and models were assessed using Akaike's information criterion and the area under the receiver operator characteristic curve on 10 random subsets of the data. We found that all models performed similarly, with the combination of cost distance and the quantity of saltmarsh performing better, but not significantly so. We compared the advantages and disadvantages of different models and also present a model averaged result. Our models suggested that the majority of saltmarshes in New South Wales were too small to have a large effect on probability of occurrence. As climate change is expected to further reduce the amount of available saltmarsh through continued mangrove incursion, coastal populations of the white‐fronted chat are expected to come under increasing threat. The conversion of grasslands to urban areas may also increase the effective distance between different populations of the species and reduce gene flow and rescue effects.     

The relationship between possum density and browse damage on kamahi in New Zealand forests

To minimize the impacts of introduced pests and to justify and prioritize pest control, managers need to know the relationship between pest density and damage. This relationship can be difficult to quantify because pest impacts can be highly variable. In New Zealand, introduced brushtail possums (Trichosurus vulpecula) browse a wide range of native forest species. However, possum browse is extremely patchy making it difficult to quantify the relationship between density and damage, meaning the benefits of reducing possum densities are poorly understood. We quantified patterns of possum browse on kamahi (Weinmannia racemosa), a common canopy tree species, at 21 forest sites that were repeat‐measured over an 8‐year period in the North Island, New Zealand, during which time possum densities fluctuated widely. We fitted a multilevel statistical model in order to quantify the relationship between possum density and browse damage while simultaneously quantifying how browse varied among trees, sites and years. Higher possum densities were associated with greater browse damage, but browse was also patchily distributed among trees at the same site, and among sites and years for a given possum density. This heterogeneity meant there was no simple density damage relationship, with the relationship differing from tree to tree and among sites and years. Our results show that at most sites reductions in possum density would have little benefit in reducing the probability of heavy browse on kamahi trees, but at a few sites there would be substantial benefits. This approach provides insights into the pattern and potential causes of variability in possum impacts, and a quantitative basis for prioritizing sites for possum control.     

Sexual dimorphism and sexual selection in a montane scincid lizard (Eulamprus leuraensis)

Sex‐based divergences in body sizes and/or shapes within a species imply that selective forces act differently on morphological features in males versus females. That prediction can be tested with data on the relationship between morphology and reproductive output in females, and between morphology and realized paternity (based on genetic assignment tests) in males. In a sample of 81 field‐collected adult Blue Mountains water skinks (Eulamprus leuraensis), males and females averaged similar overall body sizes (snout–vent lengths (SVLs)). Reproductive success (based on 105 progeny produced by the females) increased with SVL at similar rates in both sexes (as expected from the lack of sexual size dimorphism). Multiple paternity was common. Males had larger heads than females of the same body size, and (as predicted) reproductive success increased with relative head size in males but not in females. Males also had relatively longer limbs and shorter trunks than females, but we did not detect significant sex differences in selection on those traits. Reproductive success in both sexes was increased by relatively longer hind limbs. Our data clarify mating systems in this endangered species, and suggest that mating systems are diverse within the genus Eulamprus.     

Revisiting projected shifts in the climate envelopes of North American trees using updated general circulation models

Global climate models are constantly being upgraded, but it is often not clear what these changes have on climate change impact projections. We used difference maps to directly compare downscaled projections of temperature and precipitation across North America for two versions (or generations) of three different Atmospheric‐Ocean General Circulation Models (AOGCM)s. We found that AOGCM versions differed in their projections for the end of the current century by up to 4 °C for annual mean temperature and 60% for annual precipitation. To place these changes in an ecological context, we reanalyzed our work on shifts in tree climate envelopes (CEs) using the newer‐generation AOGCM projections. Based on the updated AOGCMs, by the 2071–2100 period, tree CEs shifted up to 2.4 degrees further north or 2.6 degrees further south (depending on the AOGCM) and were about 10% larger in size. Despite considerable differences between versions of a given AOGCM, projections made by the newer version of each AOGCM were in general agreement, suggesting convergence across the three models studied here. Assessing the AOGCM outputs in this way provides insight into the magnitude and importance of change associated with AOGCM upgrades as they continue to evolve through time.     

Spatial and temporal variation in host–parasitoid interactions: leafcutter ant hosts and their phorid parasitoids

1. Parasitoid–host interactions are important components of ecological communities. Although parasitoid–host interactions are strongly shaped by evolutionary history, the abundance of both the parasitoid and the host may have a role in determining the nature of the interaction once phylogenetic relationships are considered. 2. Leafcutter ants are hosts of phorid parasitoids and represent a well‐defined and specialised module within a larger network of ant–symbiont interactions. A low specificity host taxa and a positive association between host abundance and parasitoid interaction frequency were expected due to the close phylogenetic relatedness of the hosts. 3. The interactions among all species of leafcutter ants and their parasitoids were quantified in two localities with different species richness. This study also characterised the spatial‐temporal variability of these interactions, determined the patterns of parasitoid specificity and host selection, and tested for an association between host abundance and parasitoid interaction frequency. 4. Contrary to expectation, most parasitoid species were highly specialised and interaction frequency for parasitoid species was not related to host abundance. All host ant species were attacked by more than one phorid species. Some phorid species used more than one host species and showed preference for the same species over space and time, suggesting that there are physiological and/or behavioural restrictions on host use. 5. These results show that there is a tendency for specialisation even when hosts are highly similar in their ecology. From a biological control perspective, these parasitoids may be effective candidates, due to the high specificity of some species and little host‐use variation through time.     

Monoclonal Antibodies Identify a Subset of Dense Granules in Cryptosporidium parvum Zoites and Gamonts

ABSTRACT. Two monoclonal antibodies raised against purified oocysts and excysted sporozoites of Cryptosporidium parvum identified antigens located in the anterior half of sporozoites by indirect immunofluorescence microscopic assay. The monoclonal antibodies also reacted with Triton X-100-insoluble antigens of asexual and sexual stage parasites developing in epithelial cells in vitro and identified a 110 kilodalton antigen on immunoblots of sodium dodecyl sulfate-extracted oocysts. Immunoblotting reactivity was abolished by prior treatment of blotted antigen with periodic acid suggesting that the monoclonal antibodies recognize a carbohydrate or carbohydrate-dependent epitope(s). By immunoelectron microscopy, the antibodies reacted with a family of small, electron-dense granules located predominantly in the central region of merozoites and also with a population of cytoplasmic inclusions in macrogamonts. In addition, the monoclonal antibodies prominently labeled the parasitophorous vacuole membrane of all intracellular stages examined suggesting that the corresponding antigen(s) may be exocytosed from the granules to become associated with Triton X-100-insoluble components of the vacuolar membrane or cytoskeleton.     

Effects of pH on Excystation of Gregarina cuneata and Gregarina polymorpha (Eugregarinida: Gregarinidae)1

ABSTRACT. The mechanisms that signal gregarine excystation are unknown. Previous authors have demonstrated that gregarine sporozoites excyst from their surrounding oocyst in response to stimuli contained in host digestive fluids, but the role of host intestinal pH in this signaling system has not been investigated. In this study, an in vitro assay is used to quantify the effects of 3 pH levels (6.1, 7.0, 8.0) on the excystation of two gregarine species, Gregarina cuneata and Gregarina polymorpha. Both gregarine species excyst at all three pH levels, but there are significant within and among species differences in excystation rate and cumulative excystation over time. Gregarina cuneata excysts more rapidly at pH 6.0 and G. polymorpha excysts more rapidly at pH 8.0. Cumulative excystation is maximized at pH 6.0 for G. cuneata and at pH 7.0 for G. polymorpha. Hydrogen ion mediated excystation may lead to the formation of foci for subsequent establishment or migration and may play a role in parasite site specificity.