M Pope

A large-scale “experiment” to examine the effects of landscape context and habitat fragmentation on mammals

Abstract A large-scale “experiment” was undertaken in a 100 000 ha region of south-eastern Australia to examine the response of mammals to landscape context, habitat fragmentation and other factors. The investigation examined the presence and abundance of mammals in three broad categories of sites for which there were strong contrasts in the composition of the surrounding landscape: • Large contiguous areas of Eucalyptus forest, • Areas dominated by exotic plantation softwood Radiata Pine (Pinus radiata) trees, and • Fragments of eucalypt forest surrounded by an extensive P. radiata plantation. These sites provided the basis for assessing the effects of what we term “landscape context”. Eighty-six fragments of remnant eucalypt forest of varying size, shape, isolation age and other attributes were selected by a stratified, randomization process. Forty sites were located in large contiguous areas of Eucalyptus forest and these were matched to the sites in the remnants on the basis of forest type, geology and climatic conditions. A further 40 sites were selected in areas dominated by P. radiata trees and these also were matched to sites in the remnants and those in large contiguous areas of native forest on the basis of geology and climatic conditions. Two major surveys sampled mammals in the study. Hairtubing (a technique for detecting animals from the analysis of fur collected in a small portable bait station) was utilized at all 166 sites selected in the study. Trapping and a combination of different types of hairtubing was then employed at a subset of 58 sites. Data from these surveys was used to investigate the response of mammals to landscape context, habitat fragmentation and other attributes. A sub-theme of the study was to assess the efficacy of different methods to count mammals. There were large differences in the effectiveness of the different field techniques. The best technique (best in the sense of counting most animals) varied between species, particularly in relation to body size. Trapping and smaller-sized hairtubes were superior for small mammals such as Brown Antechinus (Antechinus stuartii) and Bush Rat (Rattus fuscipes). Large hairtubes performed best in the detection of large mammals like the Common Wombat (Vombatus ursinus), Common and Mountain Brushtail Possums (Trichosurus vulpecula and Trichosurus caninus), and Swamp Wallaby (Wallabia bicolor). W. bicolor and V. ursinus showed no response to landscape context and were detected at similar rates in the remnants, sites in large contiguous areas of native forest and sites dominated by stands of P. radiata. Trichosurus spp. were recorded significantly less often in sites dominated by P. radiata trees. Landscape context effects for R. fuscipes and A. stuartii varied depending on the field methods employed to sample mammals. However, in general, R. fuscipes and A. stuartii were recorded significantly less frequently in P. radiata sites than sites in large contiguous areas of Eucalyptus forest or fragments of remnant eucalypt forest surrounded by the softwood plantation. An important finding of our work was that although some species were extremely rare in P. radiata stands, no significant differences were identified in mammal presence and abundance between sites located in large contiguous areas of Eucalyptus forest and sites in fragments of remnant eucalypt forest surrounded by the softwood plantation. This finding suggests that either: animals from potential population sources in contiguous eucalypt forest can move through the softwood plantation and colonise the remnants, or populations residing in the fragments of remnant eucalypt forest are large enough to resist local extinction. Softwood plantations are presently being expanded in south-eastern Australia, particularly on semi-cleared farmland that supports remnant fragments of native Eucalyptus forest and woodland. Our findings indicate that remnant native forest within plantations of exotic P. radiata trees are occupied by several species of native mammals even when these fragments are surrounded by extensive, largely unsuitable plantation forests that have been established for many decades. These fragments should not be cleared during efforts to expand the softwood plantation estate. Large remnants and those with particular habitat features such as a dense cover of vegetation should have priority for exemption from clearing.

THE RESPONSE OF ARBOREAL MARSUPIALS TO LANDSCAPE CONTEXT: A LARGE-SCALE FRAGMENTATION STUDY

We describe a landscape-scale study of fragmentation effects on arboreal marsupials at Tumut, southeastern Australia. Embedded within a 55000-ha plantation of exotic Monterey pine (Pinus radiata) are 192 patches of remnant Eucalyptus forest, with large contiguous areas of eucalypt forest beyond the plantation boundary. We compared presence and estimated abundance of arboreal marsupials in three broad groups of sites: remnants of native Eucalyptus forest in the P. radiata plantation; P. radiata stands in the plantation; and large areas of contiguous Eucalyptus forest surrounding the plantation. The study animals were Trichosurus vulpecula, T. caninus, Petaurus breviceps, P. norfolcensis, P. australis, Acrobates pygmaeus, Pseudocheirus peregrinus, and Petauroides volans. We used randomized, replicated statistical procedures to sample 86 eucalypt remnants varying in size, shape, and other features. We matched 40 sites in large contiguous Eucalyptus forest to those remnants, based on environment, climate, ter...

Cavity sizes and types in Australian eucalypts from wet and dry forest types–a simple of rule of thumb for estimating size and number of cavities

Abstract We describe the relationships between the number, size and type of cavities in six species of eucalypt trees from southern New South Wales (south-eastern Australia) and tree diameter, tree height, tree species and other measures. The eucalypt species studied were:-Narrow-leaved Peppermint ( Eucalyptus radiata ), Mountain Swamp Gum ( Eucalyptus camphora ), Mountain Gum ( Eucalyptus dalrympleana ), Red Stringybark ( Eucalyptus macrorhyncha ), Ribbon Gum ( Eucalyptus viminalis ), and, Broad-leaved Peppermint ( Eucalyptus dives ). E. radiata and E. macrorhyncha supported almost twice the proportion of branch-end hollows than cavities assigned to other categories. Cavities in the main trunk were the predominant hollow class in E. viminalis and E. dalrympleana . Large diameter trees were characterised by more branch-end hollows, whereas main trunk cavities were typically the most prevalent cavity type in smaller diameter stems. We identified a simple, general rule that highlights the relationships between cavities and readily measured tree attributes. Our data show that, in general, both the number of cavities and cavity size were directly proportional to tree diameter, but inversely proportional to the square root of tree height. This proportionality changed between different tree species. E. dives and E. viminalis supported, on average, larger cavities than other species, whereas the cavities in E. macrorhyncha were smaller than the other taxa sampled. This simple general relationship may make it possible to make rapid crude estimates of cavity abundance across large areas of forest by measuring simple tree attributes such as tree diameter and tree height.

HABITAT FRAGMENTATION, LANDSCAPE CONTEXT, AND MAMMALIAN ASSEMBLAGES IN SOUTHEASTERN AUSTRALIA

Abstract We examined relationships between mammalian assemblages and landscape context and habitat fragmentation in southeastern Australia. Data were gathered from spotlighting and hair sample surveys at 166 sites in 3 different spatial (landscape) contexts: remnant patches of native eucalypt forest surrounded by an extensive plantation of exotic radiata pine (Pinus radiata—86 sites), the radiata pine plantation (40 sites), and large areas of continuous native eucalypt forest that occurred at the margins of the plantation (40 sites). Continuous eucalypt forest supported more species than eucalypt patches, although some species were more common in the patch areas. All assemblages in the radiata pine sites were substantially impoverished. There was a significant patch size effect for the total mammalian assemblage and for terrestrial native mammals but not for arboreal marsupials. Bigger remnants supported an assemblage different from (and more species rich) that found in smaller remnants, particularly those <3 ha where many mammal species occurred less frequently. The landscape context and patch area effects recorded in this study have important implications for plantation design in southern Australia. Eucalypt remnants should be exempt from clearing during plantation development; larger remnants are the most important areas.

TESTING A SIMULATION MODEL FOR POPULATION VIABILITY ANALYSIS

We conducted a field-based test of the widely available generic computer simulation model VORTEX for population viability analysis (PVA). The model was used to predict the abundance of three species of arboreal marsupials in a system of 39 remnant patches of Eucalyptus forest embedded within a 5050-ha area of exotic radiata pine (Pinus radiata) forest in southeastern Australia. The marsupial species were: greater glider (Petauroides volans), mountain brushtail possum (Trichosurus caninus), and common ringtail possum (Pseudocheirus peregrinus). Predictions were generated for scenarios in which: (1) the rate of exchange of animals between patches was varied, (2) different models for the migration of animals between habitat patches were invoked, (3) different levels of immigration (or dispersal) from a large, neighboring source area were simulated, (4) variations in habitat quality between remnant patches were incorporated in the model, and (5) the influence of the pine matrix surrounding the remnant patches...

Arboreal marsupial incidence in eucalypt patches in south-eastern australia : A test of Hanski's incidence function metapopulation model for patch occupancy

The results of field tests are described of a simple model for the occupancy of habitat patches developed by Hanski. Patch occupancy was predicted for several species of arboreal marsupials in a system of fragmented patches of Eucalyptus forest in the Tumut region of southern New South Wales (NSW) in south-eastern Australia. The species of arboreal marsupials for which the model was tested were: common brushtail possum (Trichosurus vulpecula), mountain brushtail possum (Trichosurus caninus), common ringtail possum (Pseudocheirus peregrinus), and greater glider (Petauroides volans). Predictions of the model were compared against actual data on patch occupancy gathered from extensive field surveys. Four sub-models were tested for each of the four species of arboreal marsupials: with and without rescue effects and with and without mainland effects (i.e. dispersal from large population source areas). These sub-models were tested by deriving model parameters from a subset of 40 patches and then applying the model to make predictions of patch occupancy in an array of 86 other patches of remnant Eucalyptus forest habitat. Comparisons were then made between the actual values for patch occupancy found during field surveys and the probabilities of patch occupancy predicted by the model. Our analyses revealed large differences in the results for different species. In the case of P. peregrinu there were several models for which it was not possible to derive the parameter estimates required by the model (i.e. relationships for extinction and colonisation as a function of patch size and patch isolation). The ability of the species to persist at low density in the surrounding landscape matrix may have precluded the calculation of these estimates. There was reasonable congruence between predictions and actual field data for patch occupancy for P. volans and also for most sub-models for T. vulpecula. Conversely, none of the sub-models for T. caninus produced results that were consistent with the observed data on patch occupancy for this species. The reasons for the marked differences in results for T. caninus and T. vulpecula are not clear, but they indicate that knowledge of the response of one species to disturbance (e.g. habitat fragmentation) may not necessarily provide a useful guide to the possible response of other taxa, including those that are very closely related.

Patch use by the greater glider (Petauroides volans) in a fragmented forest ecosystem. I. Home range size and movements

This paper examines home-range attributes of 40 greater gliders (Petauroides volans) in five patches of remnant eucalypt forest surrounded by stands of radiata pine (Pinus radiata) near Tumut in south-eastern Australia. Fixed-kernel smoothing methods were used to estimate home-range size for P. volans. For males, home-range size varied from 1.38–4.10 ha (mean = 2.6 ± 0.8 ha, n = 12) and was significantly larger (P < 0.05) than for females (1.26–2.97 ha, mean = 2.0 ± 0.6 ha, n = 11). Home-range size increased significantly with increasing patch size and reduced patch population density. Thus, small patches had more animals per unit area with smaller home ranges and greater home-range overlap. Our findings illustrate flexibility in the use of space by P. volans. Such results have not previously been reported for P. volans or any other species of arboreal marsupial. Considerable home-range overlap (at 95th percentile isopleth level) was observed between male and female P. volans. Pairs of females also exhibited home-range overlap. Males tended to maintain home ranges exclusive of other males, although some shared common areas. Contrary to the large variations observed in home-range area, core areas (50th isopleth) remained relatively constant, regardless of patch size, population density or sex. This may indicate that core areas are an essential requirement for individuals and resources they contain cannot be shared with congeners.

Patch use by the greater glider (Petauroides volans) in a fragmented forest ecosystem. II. Characteristics of den trees and preliminary data on den-use patterns

This paper presents the results of a study of the use of den trees by the greater glider (Petauroides volans) in five patches of remnant eucalypt forest embedded within an extensive radiata pine (Pinus radiata) plantation near Tumut in south-eastern Australia. Radio-tracking was used to identify 171 den trees occupied by 40 animals over 948 animal-tracking days between September 1997 and September 1998. All radio-tracked P. volans used multiple den trees. Males used significantly more den trees than females and a greater proportion of these were used for single visits. Males also used fewer new den trees over the study period in the smaller patches, although they still used more than females. In the larger patches, males and females used similar numbers of den trees. Commonly used den trees tended to be situated in (or close to) core areas of an individual’s home range. Den tree sharing, either concurrently or independently, was predominantly between adult males and females, or between adults and their young. Trees most likely to be used by more than one individual had the same characteristics as trees that had the highest probability of use per se – that is, they were of large ‘average size’.

Foliage Chemistry Influences Tree Choice and Landscape Use of a Gliding Marsupial Folivore

The chemical quality of forage may determine landscape use and habitat quality for some herbivorous species. However, studies that investigate the relationship between foliar chemistry and foraging choices in wild vertebrates are rare. Petauroides volans (the greater glider) is unique among Australian marsupial folivores because it glides. It also frequently consumes foliage from both major Eucalyptus subgenera, Eucalyptus (common name “monocalypt”) and Symphyomyrtus (common name “symphyomyrtle”), which differ markedly in their foliar chemistry. Such differences are thought to be a product of co-evolution that also led to guild-specific plant secondary metabolite (PSM) specialization among other marsupial eucalypt folivores. To explore whether foliar chemistry influences tree use, we analyzed foliage from eucalypt trees in which we observed P. volans during a radio tracking study and from eucalypt trees in which animals were never observed. We used a combination of chemical assays and near infrared spectrophotometry (NIRS) to determine concentrations of nitrogen (N), in vitro available nitrogen (AvailN), and in vitro digestible dry matter (DDM) from foliage sampled from the monocalypt and symphyomyrtle species, and total formylated phloroglucinol compounds (FPCs) and sideroxylonals (a class of FPCs) from the symphyomyrtle species (FPCs do not occur in monocalypts). Tree size and spatially-dependent, intraspecific variations in sideroxylonals and DDM concentrations in the symphyomyrtle foliage and of N, AvailN, and DDM in the monocalypt species were important indicators of tree use and habitat suitability for P. volans. The results i) demonstrate that guild-specific PSMs do not always lead to guild-specific foraging; ii) provide a compelling co-evolutionary case for the development of gliding in P. volans; and iii) have implications for the management and conservation of this and other folivorous species.

How effective is spotlighting for detecting the greater glider (Petauroides volans)

The efficacy of spotlighting as a field survey technique for detecting the greater glider (Petauroides volans) was assessed by comparing the precise location of radio-tracked animals with locations determined simultaneously from spotlighting searches. Radio-collars were fitted to 20 greater gliders in three eucalypt patches embedded within an extensive radiata pine (Pinus radiata) plantation near Tumut in south-eastern New South Wales. Our success rate for detecting collared animals was low, even when survey effort was increased. These findings suggest that spotlighting underestimates actual population size. A further, properly designed study, in different forest types is needed to provide precise estimates of the magnitude of the bias in counts of P. volans obtained by spotlighting.