A simple landscape-scale test of a spatially explicit population model: patch occupancy in fragmented south-eastern Australian forests

The results of a landscape‐scale test of ALEX, a widely used metapopulation model for Population Viability Analysis (PVA), are described. ALEX was used to predict patch occupancy by the laughing kookkaburra and the sacred kingfisher in patches of eucalypt forest in south‐eastern Australia. These predictions were compared to field surveys to determine the accuracy of the model. Predictions also were compared to a “naïve” null model assuming no fragmentation effects.
The naïve null model significantly over‐predicted the number of eucalypt patches occupied by the sacred kingfisher, but the observed patch occupancy was not significantly different from that predicted using ALEX. ALEX produced a better fit to the field data than the naïve null model for the number of patches occupied by the laughing kookaburra. Nevertheless, ALEX still significantly over‐predicted the number of occupied patches, particularly remnants dominated by certain forest types – ribbon gum and narrow‐leaved peppermint. The predictions remained significantly different from observations, even when the habitat quality of these patches was reduced to zero. Changing the rate of dispersal improved overall predicted patch occupancy, but occupancy rates for the different forest types remained significantly different from the field observations. The lack of congruence between field data and model predictions could have arisen because the laughing kookaburra may move between an array of patches to access spatially separated food and nesting resources in response to fragmentation. Alternatively, inter‐specific competition may be heightened in a fragmented habitat. These types of responses to fragmentation are not incorporated as part of traditionally applied metapopulation models. Assessments of predictions from PVA models are rare but important because they can reveal the types of species for which forecasts are accurate and those for which they are not. This can assist the collection of additional empirical data to identify important factors affecting population dynamics.     

Host preferences and behaviour of oxpeckers: co-existence of similar species in a fragmented landscape

The host preferences and behaviour of red-billed and yellow-billed oxpeckers (Buphagus erythrorynchus and Buphagus africanus) were studied at two locations in Kenya and combined with previously published data from East and South Africa. Red-billed oxpeckers are generally more common and have a greater niche breadth with respect to host preferences than yellow-billed oxpeckers, possibly due to the behavioural dominance of the latter. Otherwise, the host preferences are remarkably similar: both prefer larger species of ungulates and are found predominantly on species with manes. There are also no significant differences in the time–activity budgets of the two species controlling for site and host species, and differences in the proportion of time spent on different body parts of hosts are small in absolute magnitude even when statistically significant. Despite these and other basic ecological similarities, no evidence for competitive displacement was detected by comparing host preferences in areas of sympatry with areas of allopatry, even though each species appears to depress the population size of the other when sympatric. Traditional single-community competition theory cannot explain the geographical ecology of these two species. Instead, co-existence appears to be dependent on the patterns of extinction and colonization characterized by metapopulations distributed among a fragmented habitat.     

Plant species diversity in Mediterranean old-growth forests: A case study from central Italy

Abstract

To investigate the differences in understorey composition and diversity between old-growth and managed forests, we analyzed an old-growth and a managed beech stand in the same area displaying similar abiotic features. We considered variations in understorey species composition and richness. The sampled understorey species were characterized in terms of functional traits, Ellenberg's indicator values and taxonomic distinctness; next, we calculated four different pairwise plot-to-plot dissimilarity matrices based on species composition, functional traits, Ellenberg's indices and taxonomic distances. We applied a permutational multivariate extension of ANOVA to test whether the forest stands significantly differ in the considered features. Indicator values of all plant species in managed and old-growth stands were evaluated.

The old-growth forest had a higher species richness; permutational analysis of variance showed significant differences between the two stands in plant species composition, functional traits, Ellenberg indices and taxonomic distances. Indicator species analysis highlighted 14 indicator species for the unmanaged stand, while only 3 indicators were found for the managed one.

The results suggest that forest management determines ecological differences that strongly affect plant species composition.

The knowledge of natural stands dynamics could allow development of new approaches and practices in forest management focusing on biodiversity conservation.     

Cross-sectional vs. longitudinal research: a case study of trees with hollows and marsupials in Australian forests

How different are insights based on cross-sectional studies from those of longitudinal investigations? We addressed this question using a detailed case study encompassing a rare suite of inter-connected cross-sectional and longitudinal investigations that have spanned the past two decades and included work on: (1) the decay and collapse of large-cavity forest trees (termed “trees with hollows”), (2) populations of a suite of species of arboreal marsupials that are reliant on trees with hollows as nesting and denning sites, and (3) relationships between the abundance, type, and condition of trees with hollows and the presence, abundance, and species richness of these animals. Our case study was from the montane ash eucalypt forests of the Central Highlands of Victoria, southeastern Australia. Our longitudinal studies led to new insights that either would not have been possible from a cross-sectional study, or which were unexpected because they did not conform, or only partially conformed, to postulated responses made at the outset based on the results of earlier research. These new insights included: (1) a substantial slowing in rates of tree fall between 1997 and 2006, which were significantly lower than predicted from earlier data gathered between 1983 and 1993, (2) no evidence for a decline in populations of almost all species of arboreal marsupials between 1997 and 2007, despite the loss of nearly 14% of the measured population of trees with hollows during that time, (3) changes in nest tree selection by some species of arboreal marsupials in response to these changes in hollow availability, (4) concentration effects, in which populations of animals used the declining tree hollow resource more intensively, and (5) evidence for significant rainfall effects on temporal changes in animal abundance. Our case study underscored the additional ecological insights that can be generated from longitudinal studies, including how relationships between biota and their habitat can change over time. Understanding these temporal changes is essential for informed forest management and biodiversity conservation, and points toward the need for greater use of longitudinal data sets in ecology.     

Seed banks in Danish deciduous forests: species composition, seed influx and distribution pattern in soil

Samples of soil from six forest stands of different age and composition were collected, and the seedlings emerging during germination experiments were recorded Total seed bank densities varied between 2230 and 15,630 seeds m⁻² The seed bank size was positively correlated with the yearly seed influx, which constituted from 400 to 2720 seeds m⁻² Juncus effusus dominated the seed banks with generally 2000 to 3300 seeds m⁻², to exceptionally 10820 seeds m⁻² Seeds of Rubus idaeus, Betula pubescens and Carex spp were also abundant in the soil Similar numbers of species were present in the seed banks and vegetation, but only 7-48% were species in common Anemochorous species were more frequent in soil than above-ground, while zoochorous species were rare in soil but abundant in the vegetation A measure of the occurrence of seeds in relation to soil depth was designed Seeds of species with short-term survival in soil (e g Anemone nemorosa, Epilobium angustifolium, Oxalis acetosella and Stellaria holostea) were confined to the top soil, while many well known long-term survivors (e g Carex piluhfera, Poa annua, Rubus idaeus and Stellaria media) were found predominantly deep in the soil The horizontal distribution of seeds of herbaceous species forming short-term seed banks was largely random, while seeds of herbs capable of long-term survival in soil were significantly aggregated Except for one old and species-poor site, the dormant flora indicated generally high levels of disturbance in the past     

A power function for forest structure and regeneration pattern of pioneer and climax species in patch mosaic forests

The DBH-class distribution in natural deciduous broad-leaved forests was elucidated with a power function. A power function (y=ax ^b, y: stem density, x: represents DBH class, a and b: constants) fits the distribution better than an exponential function (y = a exp bx). The parameter b in the power function is approximately –2. This means that the natural forests studied have a patch-mosaic structure and that tree cohorts regenerate from gaps. Parameter a implies the number of juveniles, and b means size-dependent mortality. The value of –2 for parameter b means that when trees in a given DBH class double their DBH, the density of the size class should decrease by one-fourth. This phenomenon results from self-thinning and is caused by horizontal space competition among trees, called the `tile model'. The parameter describing DBH-class distribution for a forest with self-thinning patches should be approximately –2. I call this the `–2 power law' for DBH-class distribution. In a typical natural forest dominated by deciduous broadleaf tree species, trees are recognized as pioneer or climax species by the parameters describing their regeneration patterns. When I applied the power functional model to the DBH-class distribution of each dominant species, in pioneer species parameter a was high and b was less than –2 (markedly less than zero), suggesting that there are many juveniles, but mortality is high. On the other hand, in climax species parameter a was low value and the value of b was larger (negative, but closer to zero), suggesting that there are not many juveniles, but mortality is low. A power-function analysis of DBH-class distribution can be used to clarify the patch mosaic structure of a forest, and to clarify the regeneration pattern of pioneer and climax species by applying the function for each species.     

A framework for assessing the vulnerability of species to climate change: a case study of the Australian elapid snakes

Frameworks that provide a system for assessing species according to their vulnerability to climate change can offer considerable guidance to conservation managers who need to allocate limited resources among a large number of taxa. To date, climate change vulnerability assessments have largely been based on projected changes in range size derived from the output of species distribution models (SDMs). A criticism of risk assessments based solely on these models is that information on species ecological and life history traits is lacking. Accordingly, we developed a points-based framework for assessing species vulnerability to climate change that considered species traits together with the projections of SDMs. Applying this method to the Australian elapid snakes (family Elapidae), we determined which species may be particularly susceptible in the future and assessed broad-scale biogeographic patterns in species vulnerability. By offering a more comprehensive and rigorous method for assessing vulnerability than those based solely on SDMs, this framework provides greater justification for resource allocation, and can help guide decisions regarding the most appropriate adaptation strategies.     

A mathematical model for the temporal pattern of a population structure,with particular reference to the flour beetle: II. Competition between species

The effect of competition between species is considered in terms of a mathematical model. It is found that, except for special relations among the parameters, only one species should remain, as is found experimentally. It is also found that unless new factors arise in the competition, one can calculate an index to predict which of the two species is most likely to become extinct. The index involves quantities measured from isolated populations. A preliminary extimate yields satisfactory values when compared with the experimental results of competition.     

A possible contribution of phenomenology to ethology: Application to a behaviour pattern in the mouse

Classical ethology encourages a causal approach to animal behaviour, using Tinbergen's four questions concerning evolution, function, mechanism and development of behaviour. It sets aside the study of mental processes, which could otherwise help to unify our picture of the relationships between animal and environment. Here the steps in research focused on the psychological meaning of a peculiar behaviour in the mouse — carrying its tail — and what this implies regarding the mouse's cognitive world are given. Initial empirical observations suggested epistemic choices concerning space and object notions in the mouse; this led us to go beyond the first stage in exploring the significance of this behaviour. Later experiments showed the limitations of an explanation based on a cause-effect relationship. An interpretative model integrating a phenomenological conceptual framework is proposed.     

Simulating carbon dioxide exchange rates of deciduous tree species: evidence for a general pattern in biochemical changes and water stress response

Background and Aims

Deciduous trees have a seasonal carbon dioxide exchange pattern that is attributed to changes in leaf biochemical properties. However, it is not known if the pattern in leaf biochemical properties – maximum Rubisco carboxylation (V_cmax) and electron transport (J_max) – differ between species. This study explored whether a general pattern of changes in V_cmax, J_max, and a standardized soil moisture response accounted for carbon dioxide exchange of deciduous trees throughout the growing season.

Methods

The model MAESTRA was used to examine V_cmax and J_max of leaves of five deciduous trees, Acer rubrum ‘Summer Red’, Betula nigra, Quercus nuttallii, Quercus phellos and Paulownia elongata, and their response to soil moisture. MAESTRA was parameterized using data from in situ measurements on organs. Linking the changes in biochemical properties of leaves to the whole tree, MAESTRA integrated the general pattern in V_cmax and J_max from gas exchange parameters of leaves with a standardized soil moisture response to describe carbon dioxide exchange throughout the growing season. The model estimates were tested against measurements made on the five species under both irrigated and water-stressed conditions.

Key Results

Measurements and modelling demonstrate that the seasonal pattern of biochemical activity in leaves and soil moisture response can be parameterized with straightforward general relationships. Over the course of the season, differences in carbon exchange between measured and modelled values were within 6–12 % under well-watered conditions and 2–25 % under water stress conditions. Hence, a generalized seasonal pattern in the leaf-level physiological change of V_cmax and J_max, and a standardized response to soil moisture was sufficient to parameterize carbon dioxide exchange for large-scale evaluations.

Conclusions

Simplification in parameterization of the seasonal pattern of leaf biochemical activity and soil moisture response of deciduous forest species is demonstrated. This allows reliable modelling of carbon exchange for deciduous trees, thus circumventing the need for extensive gas exchange experiments on different species.Key words: Carbon budget, deciduous trees, modelling, MAESTRA, soil moisture, species response, transpiration, Acer rubrum, Betula nigra, Quercus nuttallii, Q. phellos, Paulownia elongata     

Of spates and species: responses by interstitial water mites to simulated spates in a subtropical Australian river

The ‘hyporheic refuge hypothesis’ predicts that the hyporheic zone, the saturated sediments below and alongside rivers and streams, is a refuge from the scouring effects of spates for many aquatic invertebrates including water mites. We tested this hypothesis in two lateral gravel bars and two riffles in a subtropical Australian river by collecting water mites from the hyporheic zone at two depths (10 and 50 cm) at two‘pre-flood’ sampling times before experimentally diverting water through the sites for 14 h to simulate a spate. Taxon richness of mites washigh (46 taxa) and dominated by the Prostigmata, with nearly half the species being new to science. Oribatids were also common at the four sites. Samples were collected twice during each ‘spate’, and again soon after flow was returned to normal. The experimental spate induced changes in the strength and even direction of subsurface-surface water exchange; however, these changes seldom persisted after the experiment, nor after a subsequent natural spate. The hyporheic refuge hypothesis was not supported by our water mite data. Neither during nor shortly after the experimental spates did we find more epigean (surface-dwelling) water mites in downwelling zones where surface streamwater enters the hyporheic zone, demonstrating that these mites were not using the hyporheic zone as a refuge at these locations. There was also no evidence for a ‘wash out’ effect, because hyporheic mitedensities did not significantly decline late in the spate. Our data indicate that floods of the low magnitude simulated in this study apparently do not pose a lasting disturbance for hypogean water mites. The fact that the same response was found at four sites indicates that the hyporheic refuge hypothesis may not always be an appropriate explanation for rapid post-flood recolonisation. Possibly, the use of the hyporheic zone as a refuge from floods may be dictated by the strength of the disturbance and substrate composition and stability.     

Sustainability of threatened species displayed in public aquaria,with a case study of Australian sharks and rays

Zoos and public aquaria exhibit numerous threatened species globally, and in the modern context of these institutions as conservation hubs, it is crucial that displays are ecologically sustainable. Elasmobranchs (sharks and rays) are of particular conservation concern and a higher proportion of threatened species are exhibited than any other assessed vertebrate group. Many of these lack sustainable captive populations, so comprehensive assessments of sustainability may be needed to support the management of future harvests and safeguard wild populations. We propose an approach to identify species that require an assessment of sustainability. Species at risk of extinction in the wild were considered to be those assessed as threatened (CR, EN or VU) on the IUCN Red List of Threatened Species, or data deficient species that may be at an elevated risk of extinction due to life history traits and habitat associations. We defined sustainable captive populations as self-maintaining, or from a source population that can sustain harvest levels without risk of population declines below sustainable levels. The captive breeding and wild harvest records of at risk species displayed by Australian aquaria were examined as a case study. Two species, largetooth sawfish Pristis pristis and grey nurse shark Carcharias taurus, were found to have unsustainable captive populations and were identified as high priorities for comprehensive sustainability assessments. This review highlights the need for changes in permitting practices and zoo and aquarium record management systems to improve conservation outcomes for captive elasmobranchs.     

Of spates and species: responses by interstitial water mites to simulated spates in a subtropical Australian river

The 'hyporheic refuge hypothesis' predicts that the hyporheic zone, the saturated sediments below and alongside rivers and streams, is a refuge from the scouring effects of spates for many aquatic invertebrates including water mites. We tested this hypothesis in two lateral gravel bars and two riffles in a subtropical Australian river by collecting water mites from the hyporheic zone at two depths (10 and 50 cm) at two 'pre-flood' sampling times before experimentally diverting water through the sites for 14 h to simulate a spate. Taxon richness of mites washigh (46 taxa) and dominated by the Prostigmata, with nearly half the species being new to science. Oribatids were also common at the four sites. Samples were collected twice during each 'spate', and again soon after flow was returned to normal. The experimental spate induced changes in the strength and even direction of subsurface-surface water exchange; however, these changes seldom persisted after the experiment, nor after a subsequent natural spate. The hyporheic refuge hypothesis was not supported by our water mite data. Neither during nor shortly after the experimental spates did we find more epigean (surface-dwelling) water mites in downwelling zones where surface streamwater enters the hyporheic zone, demonstrating that these mites were not using the hyporheic zone as a refuge at these locations. There was also no evidence for a 'wash out' effect, because hyporheic mitedensities did not significantly decline late in the spate. Our data indicate that floods of the low magnitude simulated in this study apparently do not pose a lasting disturbance for hypogean water mites. The fact that the same response was found at four sites indicates that the hyporheic refuge hypothesis may not always be an appropriate explanation for rapid post-flood recolonisation. Possibly, the use of the hyporheic zone as a refuge from floods may be dictated by the strength of the disturbance and substrate composition and stability.     

Theoretical expectations for thresholds in the relationship between number of wood-living species and amount of coarse woody debris: A study case in spruce forests

To identify thresholds in the relationship between the number of species in viable populations and habitat availability is useful for nature conservation. However, to obtain such empirical data may be extremely laborious. Many saproxylic (wood-living) species are under threat because there is little coarse woody debris (CWD) in managed forests. Based on computer simulations of CWD dynamics, and information about the substrate requirements of red-listed saproxylic species, we conclude that it is unlikely that any specific quantity of CWD can be defined as the extinction threshold for large numbers of species, since different species are specialists in utilising different types of CWD. In our analysis, we identified a curvilinear relationship between total CWD and the number of red-listed species in viable populations, even assuming that there were sharp extinction thresholds for individual species. Thus, it is highly unlikely that it will ever be possible to identify simple targets for maintenance of CWD based on extinction thresholds for the whole community of saproxylic species. Instead other strategies are necessary when formulating conservation targets.     

Forces structuring tree squirrel communities in landscapes fragmented by agriculture: species differences in perceptions of forest connectivity and carrying capacity

The North American red squirrel ( Tamiasciurus hudsonicus ) has expanded its range into the central hardwoods of the United States in conjunction with increasing forest fragmentation and declining gray squirrel ( Sciurus carolinensis ) populations. We used translocation experiments and patch occupancy data to test for interspecific differences in mobility and sensitivity to habitat loss and modification by agriculture. We released squirrels in fencerows to test the hypothesis that gray squirrels display inferior mobility relative to red and fox ( S. niger ) squirrels. Elapsed time to movement from fencerows for 76 individuals increased with distance to forest patches and harvesting of crops. Gray and red squirrels took longer to move from fencerows than fox squirrels, and gray squirrels were less successful at moving from fencerows than red and fox squirrels. Ecologically scaled landscape indices revealed the degree to which interspecific differences in mobility and individual area requirements accounted for the occurrence of these species across landscapes. Gray squirrel distribution was constrained both by individual area requirements and dispersal ability. Occurrence of red and fox squirrels was related to patch size but was unaffected by landscape connectivity.     

Twin-to-twin transfusion syndrome: a case report. Antepartum prediction of underlying placental vascular pattern in monochorionic twin pregnancies may be possible.

A case of twin-to-twin transfusion syndrome is described. Comparing data of serial antepartum ultrasonography with a haemodynamic model suggests the possibility of predicting the underlying placental vascular anatomy. It is suggested that serial ultrasonography, including full biometry, pulsatility indices of the umbilical arteries, foetal echocardiography, assessment of amniotic fluid indices and foetal bladder filling could serve as ultrasound parameters for pattern recognition of the underlying placental vascular anomaly. Biometry should be plotted serially in a difference/average plot. Future application of such intensive ultrasound monitoring in monochorionic twins, as soon as monochorionicity is established, may distinguish those monochorionic twins who may benefit from treatment from those whom it would be better only to observe.