Impacts of climate change and urban development on the spotted marsh frog (Limnodynastes tasmaniensis)

Climate change and urbanization are among the most serious threats to amphibians, although little is known about their combined effects. We used a predictive spatial habitat suitability model to explore the potential impacts of climate change and urban development on the spotted marsh frog (Limnodynastes tasmaniensis) on the urban‐fringe of Melbourne, Australia. The CSIRO climate‐change predictions for the region indicate likely temperature increases of 3°C, and annual rainfall reductions of around 200 mm by the year 2070. Much of the study area overlaps a region that has been identified as one of the city's growth corridors. We used Bayesian logistic regression modelling to estimate current and future habitat suitability of pond sites in the Merri Creek catchment, exploring a range of best‐ to worst‐case scenarios through the use of hydrological and urbanization models. Our predictions for 2070, even under a moderate climate‐change scenario, suggest that the majority of ponds in the study area will be dry throughout much of the year. This has obvious implications for L. tasmaniensis, which is an aquatic breeding species. However, in the short term, urbanization is likely to have a more significant effect on the distribution of L. tasmaniensis in the Merri Creek catchment, particularly if development moves beyond the current urban growth boundary. The combined effects of climate change and urbanization could have a profound impact on the species, potentially causing it to disappear from within the study area. We provide recommendations for including such predictive models in urban planning and restoration activities to prepare for future conservation challenges.     

Fluvial landscape ecology: addressing uniqueness within the river discontinuum

1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio‐temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept. 2. At coarse spatial scales, the hierarchical patch dynamics perspective describes each river network as a unique, patchy discontinuum from headwaters to mouth. The discontinuum is comprised of a longitudinal series of alternating stream segments with different geomorphological structures. Each confluence in the steam network further punctuates the discontinuum because the sudden change in stream characteristics can create a `gap' in the expected pattern of downstream transitions. The discontinuum view recognises general trends in habitat characteristics along the longitudinal profile, but creates a framework for studying and understanding the ecological importance of each stream's individual pattern of habitat transitions along longitudinal, lateral or vertical vectors at any scale. 3. Object‐oriented modelling and programming techniques provide a means for developing robust, quantitative simulation models that describe the dynamic structure of patch hierarchies. Such models can simulate how the structure and function of lotic ecosystems are influenced by the landscape context of the system (the ecological conditions within which the system is set) and the metastructure (structural characteristics and juxtaposition) of finer‐scale patches comprising the system. 4. A simple object‐oriented, multiscale, discontinuum model of solute transformation and biological response along a stream channel illustrates how changing the branching pattern of a stream and the arrangement of its component patches along the downstream profile will result in substantial changes in predicted patterns of solute concentration and biotic community structure. 5. The importance of context, structure, and metastructure in determining lotic ecosystem function serves to underscore 27 ) concept that `every stream is likely to be individual.' Advancing the discipline of fluvial landscape ecology provides an excellent opportunity to develop general concepts and tools that address the individual character of each stream network and integrate the concept of `uniqueness within the river discontinuum' into our ecological understanding of rivers and streams.     

Genotypic and phenotypic variation in diatom silicification under paleo‐oceanographic conditions

Diatoms have co‐evolved with the silicon cycle and are largely responsible for reducing surface concentrations of silicate in the ocean to their present levels. We quantify silicification in marine diatoms at a range of high silicate concentrations representative of environments found over their geological history. The species examined include Stephanopyxis turris, an ancient centric species found throughout the Cenozoic, Thalassiosira pseudonana and Thalassiosira weissflogii, two younger centric species, and two pennate ecotypes of Staurosirella pinnata isolated from different nutrient regimes. Frustule thickness and micromorphological structure are strongly affected by silicate concentration. All species become increasingly silicified with silicate concentrations at concentrations vastly in excess of surface ocean concentrations today. In contrast, the half‐saturation constant for silicate uptake for most modern diatoms is below 2 μm . Based on the results, we hypothesize that silicate uptake is multiphasic in diatoms and that multiple silicate transport systems may have evolved in response to decreases in surface silicate concentration over geological time. The oldest species examined is more heavily silicified than the more modern species, presumably reflecting the conditions under which it originated. Yet diversification in silicification can be rapid, as illustrated by greater silicification in onshore versus the offshore ecotype of the same modern species. This work suggests that silicification of fossil frustules may eventually provide a paleoproxy for surface silicate concentrations over the Cenozoic, although development of species‐specific calibrations will be necessary and the effects of a range of environmental conditions must be investigated.     

Mismatches between breeding success and habitat preferences in Hen Harriers Circus cyaneus breeding in forested landscapes

During the past century, the upland breeding areas of Hen Harriers in Ireland have been extensively afforested. There is no evidence that this species avoids breeding in heavily forested landscapes and, indeed, young commercial forests in their second rotation are often selected as nest‐sites. However, Hen Harriers have coexisted with these forested areas for only a few decades and it is possible that such landscapes are suboptimal. We examined the relationship between breeding success and habitat using a dataset spanning three years and four study areas in the south and west of Ireland. We assessed whether nest success and fledged brood size were related to habitat type, both at the nest‐site and in the surrounding landscape. Neither measure of breeding productivity was related to total forest cover or to percentage cover of closed canopy forest in the landscape. However, in a subset of areas, high cover of second‐rotation pre‐thicket (young forests planted on land from which a first rotation has already been harvested) in the surrounding landscape was associated with low levels of breeding success. This may be due to factors related to predation, disturbance or prey availability. The fact that second‐rotation pre‐thicket is a preferred habitat for nesting in Ireland suggests that Hen Harriers may be making suboptimal decisions in the landscapes available to them.     

Habitat use by the inland carpet python (Morelia spilota metcalfei: Pythonidae): Seasonal relationships with habitat structure and prey distribution in a rural landscape

Abstract Squamate reptiles are significant components of woodland vertebrate communities in eastern Australia, but their ecology is poorly understood. We investigated seasonal variation in habitat use by the Inland Carpet Python, Morelia spilota metcalfei Wells and Wellington (Pythonidae), a threatened snake that inhabits the woodland environments of the Murray–Darling Basin. Nine pythons were radiotracked within and near the Mount Meg Flora and Fauna Reserve in north‐eastern Victoria to investigate how habitat structure and prey distribution (namely, that of the European Rabbit, Oryctolagus cuniculus L. (Leporidae)) influenced seasonal movement patterns. Data were analysed over three spatial scales to allow firm interpretations regarding resource selection. Pythons exhibited distinct seasonal trends in habitat use. During the cooler spring months, snakes chose warm, well‐insulated microhabitats, primarily rocky outcrops on north‐ and north‐west‐facing hillsides. Pythons moved widely during the summer months, apparently in search of prey. Snake localities could be readily linked to rabbit distribution at this time. Specifically, snakes moved to more open, disturbed habitats that contained a high density of rabbits, and consistently selected microhabitats in close proximity to rabbit burrows. In autumn, habitat use was transitional, as snakes progressively returned to the rocky hillsides where they overwintered. Thus, trends in habitat use were influenced by the snakes' thermoregulatory and foraging strategies. Careful management of specific habitats and feral prey populations is required to conserve populations of this endangered snake.