Papers by William D Stock
Conserving Africa's Mega-Diversity in the Anthropocene
from Part II - Theoretical Advances in Savanna Ecolog
Restoration Ecology, 2004
Recent efforts to clear invasive plants from the fynbos of South Africa forces managers to think ... more Recent efforts to clear invasive plants from the fynbos of South Africa forces managers to think about how N 2-fixing invasives have altered ecosystem processes and the implications of these changes for community development. This study investigated the changes in nitrogen (N) cycling regimes in fynbos with the invasion of Acacia saligna, the effects of clear-cutting acacia stands on soil microclimate and N cycling, and how altered N resources affected the growth of a weedy grass species. Litterfall, litter quality, soil nutrient pools, and ion exchange resin (IER)-available soil N were measured in uninvaded fynbos, intact acacia, and cleared acacia stands. In addition, a bioassay experiment was used to ascertain whether the changes in soil nutrient availability associated with acacia would enhance the success of a weedy grass species. Acacia plots had greater amounts of litterfall, which had higher concentrations of N. This led to larger quantities of organic matter, total N, and IER-available N in the soil. Clearing acacia stands caused changes in soil moisture and temperature, but did not result in differences in IER-available N. The alteration of N availability by acacias was shown to increase growth rates of the weedy grass Ehrharta calycina, suggesting that secondary invasions by nitrophilous weedy species may occur after clearing N 2-fixing alien species in the fynbos. It is suggested that managers use controlled burns, the addition of mulch, and the addition of fynbos seed after clearing to lower the levels of available N in the soil and initiate the return of native vegetation.
<p>The final column shows the predicted number of seeds (corrected for testa mass) required... more <p>The final column shows the predicted number of seeds (corrected for testa mass) required by a Carnaby’s Cockatoo to meet its daily minimum field metabolic rate (FMR = 726 kJ d<sup>−1</sup>) as reported by Cooper <i>et al</i>. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061145#pone.0061145-Cooper1" target="_blank">[29]</a>. <sup>*</sup>Not dehusked prior to analysis.</p
Parameters used for Leslie matrix model transition, birth, and initial conditions.
Plant and Soil, 2020
Background and aims Root-released carboxylates enhance the availability of manganese (Mn), which ... more Background and aims Root-released carboxylates enhance the availability of manganese (Mn), which enters roots through transporters with low substrate specificity. Leaf Mn concentration ([Mn]) has been proposed as a signature for phosphorus (P)-mobilising carboxylates in the rhizosphere. Here we test whether leaf [Mn] provides a signature for root functional types related to P acquisition. Methods Across 727 species at 66 sites in Australia and New Zealand, we measured leaf [Mn] as related to root functional type, while also considering soil and climate variables. To further assess the specific situations under which leaf [Mn] is a suitable proxy for rhizosphere carboxylate concentration, we studied leaf [Mn] along a strong gradient in water availability on one representative site. In addition, we focused on two systems where a species produced unexpected results.
Ecology and Evolution, 2019
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Emu, 2016
Abstract Human-wildlife conflicts around the loss and use of habitat are common reasons for speci... more Abstract Human-wildlife conflicts around the loss and use of habitat are common reasons for species being listed as threatened. In order to reduce such conflicts it is important to have a clear understanding of the resource requirements of threatened species and the environmental factors that influence the availability and continued supply of those resources. The availability of Banksia cones and temporal patterns of their use by Carnaby ‘s Black-Cockatoo (Calyptorhynchus latirostris), was measured bi-monthly in proteaceous woodlands of the Swan Coastal Plain, south-western Australia. Availability of Banksia cones was assessed at sites that differed in soil-types, time since last fire and occurrence ofPhytophthora cinnamomi. The mean number of available cones differed significantly in relation to P. cinnamomi presence and time since last fire. This study revealed a strong association between availability of Banksia cones and their consumption by Carnaby's Black-Cockatoo. Over 12 months, Carnaby's Black-Cockatoos handled approximately half of the available Banksia cones, and over three-quarters of those handled involved feeding. Banksia attenuata and B. sessilis produced the greatest number of cones, with consumption proportionate to cone availability. Understanding the patterns of availability and consumption of food resources by Carnaby's Black-Cockatoos provides critical pieces of information that will help implement more effective conservation and management to stem the decline of this species.
Fynbos, 2014
The world’s mediterranean-climate regions all have mild, winter-rain climates that have developed... more The world’s mediterranean-climate regions all have mild, winter-rain climates that have developed over the past several million years, but beyond these similarities they have distinct geological and evolutionary histories that have shaped the floras of each region. This chapter considers the historical and regional influences that have shaped the floras of MT regions, focusing on South Africa, California and Western Australia. One of the most striking differences is their positions on the respective continents, and their tectonic history, and the absence of a high latitude, terrestrial region bordering South Africa and Australia. As a result, the Cape flora does not have a clearly identified temperate element, in striking contrast with California, and this may contribute to the high level of in-situ radiation in Cape lineages. While radiations have occurred in the sclerophyllous lineages in both areas, the moist-adapted, forest communities tend to be derived from cool-temperate lineages in California and from warm, afrotropical lineages in South Africa. In both cases, these components of the flora represent greater phylogenetic diversity. The absence of temperate land masses adjacent to South Africa and Western Australia result in greater reduction in the area of mediterranean-type climate in the face of 21st century global warming. Other aspects of geology, topography and human land-use impacting the prospects for biodiversity conservation are addressed
Pine plantations near Perth, Western Australia have provided an important food source for endange... more Pine plantations near Perth, Western Australia have provided an important food source for endangered Carnaby's Cockatoos (Calyptorhynchus latirostris) since the 1940s. Plans to harvest these plantations without replanting will remove this food source by 2031 or earlier. To assess the impact of pine removal, we studied the ecological association between Carnaby's Cockatoos and pine using behavioural, nutritional, and phenological data. Pine plantations provided high densities of seed (158 025 seeds ha 21) over a large area (c. 15 000 ha). Carnaby's Cockatoos fed throughout these plantations and removed almost the entire annual crop of pine cones. Peak cockatoo abundance coincided with pine seed maturation. Pine seed had energy and protein contents equivalent to native food sources and, critically, is available in summer when breeding pairs have young offspring to feed. This strong and enduring ecological association clearly suggests that removing pine will have a significant impact on this endangered species unless restoration strategies, to establish alternative food sources, are implemented.
Journal of Hydrology, 1993
This study aimed to determine whether the ~13C levels in the foliage and twigs of four Eucalyptus... more This study aimed to determine whether the ~13C levels in the foliage and twigs of four Eucalyptus grandis clones were related to their water use efficiency (WUE). This relationship has previously been demonstrated in a number of herbaceous species but not in mature trees. The study involved accurate measurements of tree trunk growth and water use over a period of 4 months, with subsequent isotopic analysis of mature foliage from the north and south side of the canopy, and young leaves from the top of the canopy. The water use efficiencies were found to vary from 5.97 x 10-3 to 12.3 x 10 .3 m 3 m 3 Significant differences were observed between clonal-mean water use efficiencies averaged over six sampling periods. The average 613C of the mature and young foliage was found to be significantly correlated with WUE. However, the correlation was weak, suggesting that the relationship between 613C and WUE is more complex in trees than suggested in the literature on crop plants. It is suggested that differences between sample trees in carbon allocation and leaf-to-air vapour pressure deficits may account for the poor correlation between 6t3C and WUE in the four E. grandis clones studied.
IAWA Journal, 1995
The primary objective of this study was to determine the relationships between water availability... more The primary objective of this study was to determine the relationships between water availability, plant growth and selected vessel characteristics for Eucalyptus grandis and two hybrids, so as to ascertain whether these xylem characteristics predict water use efficiency. Cuttings of Eucalyptus grandis, E. grandis × camaldulensis and E. grandis × nitens were planted in 220 litre drums from which rainfall was excluded. One half of the individuals received a low watering treatment; one half received a higher watering treatment. Soil moisture depletion through root uptake was monitored weekly and the removed water replaced to maintain 60 and 80 litres in the pots of the low and high watering treatments respectively. Mean values for tangential vessel diameter, vessel frequency and vessel element length were compared for the two treatments. In E. grandis and the hybrid E. grandis × camaldulensis vessel diameter (P < 0.01 ' P < 0.05 respectively) and vessel element length (P <...
Climatic Change, 2011
Abstract The importance of ecological management for reducing the vulnerability of biodiversity t... more Abstract The importance of ecological management for reducing the vulnerability of biodiversity to climate change is increasingly recognized, yet frameworks to facilitate a structured approach to climate adaptation management are lacking. We developed a conceptual framework that can guide identification of climate change impacts and adaptive management options in a given region or biome. The framework focuses on potential points of early climate change impact, and organizes these along two main axes. First, it ...
Carnaby's Black-Cockatoo is an endangered species, with less than 50% of the original popula... more Carnaby's Black-Cockatoo is an endangered species, with less than 50% of the original population remaining (Garnett and Crowley 2000). A major threatening process includes habitat fragmentation and the removal of critical feeding resources (Cale 2003). The GSS study area in an important foraging area during the non-breeding season for Carnaby's Black-Cockatoo. Both native banksia woodlands and pine plantations have been recognised as an important food resource (Perry 1948; Saunders 1974b; Saunders 1980). ...
Plant, Cell & Environment, 2014
Widespread species often occur across a range of climatic conditions, through a combination of lo... more Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in southeastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ 13 C and δ 18 O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.
Natural abundance values of plant δ "&N give an indication as to the source of nitrogen. In parti... more Natural abundance values of plant δ "&N give an indication as to the source of nitrogen. In particular, carnivorous plants are expected to be relatively enriched due to trophic enrichment of their prey. Values of δ "&N for adult Roridula gorgonias (meanj3n02 =) are 4-9 = greater than co-occurring non-carnivorous plant species and 5n24 = greater than juvenile R. gorgonias plants. They are also 3n5-4n26 = greater than co-occurring Drosera species which, being sundews, are considered to be carnivorous. These high levels of δ "&N in adult plants are best explained as being due to access to trophically enriched N from insects. As is the case for other carnivorous plants, leaves and stems of R. gorgonias are highly ultraviolet reflective and are therefore probably attractive to potential insect prey. This is further support for this plant species being insectivorous.
Biological Conservation
We propose a general and flexible capture-recapture model in continuous time. Our model incorpora... more We propose a general and flexible capture-recapture model in continuous time. Our model incorporates time-heterogeneity, observed and unobserved individual heterogeneity, and behavioral response to capture. Behavioral response can possibly have a delayed onset and a finite-time memory. Estimation of the population size is based on the conditional likelihood after use of the EM algorithm. We develop an application to the estimation of the number of adult cannabinoid users in Italy.
Atmospheric Pollution Research
Abstract This study investigated emission factors (EFs) for CO2, CO, NO and carbonyls from labora... more Abstract This study investigated emission factors (EFs) for CO2, CO, NO and carbonyls from laboratory-based combustion of five typical vegetation types of Western Australia. A range of combustion conditions was obtained by controlling the vegetation moisture content and air flow rate. CO2, CO and NO were measured using a multi-gas monitor MultiRAE. Six carbonyls were collected using 2,4-DNPH sorbent tubes and analysed using HPLC-UV. Burns of woodland (Banksia) and forest (Jarrah) had significantly higher EFCO, with lower modified combustion efficiency (MCE) than those of tropical grass (Spinifex). Temperate grass (Veldt) fires had lower EFCO2 and higher EFCO and EFcarbonyls, and a much lower MCE than those of the tropical grass fires. EFNO were similar for woodland, forest and tropical grass but large differences in EFNO were observed for Spinifex and Veldt grass. Formaldehyde was the most abundant carbonyl emitted. Combustion conditions influenced the EFcarbonyls with larger EFs from burns with higher fuel moisture contents and/or at higher flow rates. Functions to extrapolate EFs for infrequently measured carbonyls (acetaldehyde, acetone and propionaldehyde) from EFformaldehyde were developed. The EFCO2 and EFCO were similar to values reported from field measurements for similar ecosystems in Australia, indicating the applicability of these laboratory-based results. EFs for other gases differed to those reported from bushfires in other parts of the world suggesting that to improve prediction of bushfire emissions and impacts in Australia, EFs of all fire-prone Australian vegetation types should be determined, particularly for those in close proximity to densely populated areas.
Annals of Botany
Background and Aims Ant–plant associations are widely diverse and distributed throughout the worl... more Background and Aims Ant–plant associations are widely diverse and distributed throughout the world, leading to antagonistic and/or mutualistic interactions. Ant pollination is a rare mutualistic association and reports of ants as effective pollinators are limited to a few studies. Conospermum (Proteaceae) is an insect-pollinated genus well represented in the south-western Australia biodiversity hotspot, and here we aimed to evaluate the role of ants as pollinators of C. undulatum. Methods Pollen germination after contact with several species of ants and bees was tested for C. undulatum and five co-flowering species for comparison. We then sampled the pollen load of floral visitors of C. undulatum to assess whether ants carried a pollen load sufficient to enable pollination. Lastly, we performed exclusion treatments to assess the relative effect of flying- and non-flying-invertebrate floral visitors on the reproduction of C. undulatum. For this, we measured the seed set under differe...
Forest Ecology and Management
Abstract Drought is likely to increase in intensity and frequency across most of the Mediterranea... more Abstract Drought is likely to increase in intensity and frequency across most of the Mediterranean areas due to climate change. There is thus an urgent need to assess differences in the ability of plants to withstand water stress, especially when selecting appropriate species for ecological intervention. This study focuses on Mediterranean-type ecosystems (MTEs) and identifies plant traits associated with drought resistance that are key in differentiating plant functional types in relation to water use. We further discuss how this knowledge can be used by restoration practitioners. The study was conducted in the Banksia woodlands, Southwestern Australia, and six areas across a gradient of water availability were selected. We measured twelve functional traits associated with water use in fifteen plant species. Next, we applied multivariate analyses to examine how traits varied in relation to each other, grouping species based on these traits and investigating similarities within and between functional groups and sites. Functional trait correlations were consistent with the worldwide leaf and wood economic spectra. Among the twelve traits measured, six explained most trait variation: mean xylem vessel diameter (Dave), number of xylem vessels per mm−2 (Ds), leaf mass per area (LMA), stem density (WD), foliar carbon isotope composition (δ13C), and leaf water potential at turgor loss point (πTLP). Species were clustered into five different functional groups. Differences within and between functional groups and sites are reported through their Euclidean distances. Analyses of these traits provided insights into the water-use strategies of native plants, revealing those species with greatest potential to resist water deficits. Such knowledge enables the formation of a more functionally diverse assembly of species bearing complementary traits, which in turn can be used to strengthen resistance to invasion in restored communities. This functional ecological approach is transferable to other and for application by restoration practitioners since the traits selected are relatively easy and cheap to measure and require only simple analytical approaches.
Uploads
Papers by William D Stock