Lochran W. Traill

Mechanisms driving change: altered species interactions and ecosystem function through global warming

1. We review the mechanisms behind ecosystem functions, the processes that facilitate energy transfer along food webs, and the major processes that allow the cycling of carbon, oxygen and nitrogen, and use case studies to show how these have already been, and will continue to be, altered by global warming. 2. Increased temperatures will affect the interactions between heterotrophs and autotrophs (e.g. pollination and seed dispersal), and between heterotrophs (e.g. predators-prey, parasites/pathogens-hosts), with generally negative ramifications for important ecosystem services (functions that provide direct benefit to human society such as pollination) and potential for heightened species co-extinction rates. 3. Mitigation of likely impacts of warming will require, in particular, the maintenance of species diversity as insurance for the provision of basic ecosystem services. Key to this will be long-term monitoring and focused research that seek to maintain ecosystem resilience in the face of global warming. 4. We provide guidelines for pursuing research that quantifies the nexus between ecosystem function and global warming. These include documentation of key functional species groups within systems, and understanding the principal outcomes arising from direct and indirect effects of a rapidly warming environment. Localized and targeted research and monitoring, complemented with laboratory work, will determine outcomes for resilience and guide adaptive conservation responses and long-term planning.

Demography, not inheritance, drives phenotypic change in hunted bighorn sheep

Significance Understanding the consequences that selective harvest has on a targeted trait, such as body size, is a great challenge. This is principally because it is difficult to evaluate the relative importance of the evolutionary and demographic factors that underlie a change in the distribution of a selected trait in a hunted population. Here we use a novel and recently developed two-sex integral projection model to tease apart the underlying demographic and evolutionary mechanisms of trait change in a trophy-hunted bighorn sheep population. We find that body size is weakly inherited and that subsequently demographic change, and not evolutionary change, as previously thought, is the principle driver of trait shifts in hunted bighorn sheep. Selective harvest, such as trophy hunting, can shift the distribution of a quantitative character such as body size. If the targeted character is heritable, then there will be an evolutionary response to selection, and where the trait is not, then any response will be plastic or demographic. Identifying the relative contributions of these different mechanisms is a major challenge in wildlife conservation. New mathematical approaches can provide insight not previously available. Here we develop a size- and age-based two-sex integral projection model based on individual-based data from a long-term study of hunted bighorn sheep (Ovis canadensis) at Ram Mountain, Canada. We simulate the effect of trophy hunting on body size and find that the inheritance of body mass is weak and that any perceived decline in body mass of the bighorn population is largely attributable to demographic change and environmental factors. To our knowledge, this work provides the first use of two-sex integral projection models to investigate the potential eco-evolutionary consequences of selective harvest.

Sex‐specific demography and generalization of the Trivers–Willard theory

The Trivers–Willard theory proposes that the sex ratio of offspring should vary with maternal condition when it has sex‐specific influences on offspring fitness. In particular, mothers in good condition in polygynous and dimorphic species are predicted to produce an excess of sons, whereas mothers in poor condition should do the opposite. Despite the elegance of the theory, support for it has been limited. Here we extend and generalize the Trivers–Willard theory to explain the disparity between predictions and observations of offspring sex ratio. In polygynous species, males typically have higher mortality rates, different age‐specific reproductive schedules and more risk‐prone life history tactics than females; however, these differences are not currently incorporated into the Trivers–Willard theory. Using two‐sex models parameterized with data from free‐living mammal populations with contrasting levels of sex differences in demography, we demonstrate how sex differences in life history traits over the entire lifespan can lead to a wide range of sex allocation tactics, and show that correlations between maternal condition and offspring sex ratio alone are insufficient to conclude that mothers adaptively adjust offspring sex ratio.

50/500 rule and minimum viable populations: response to Jamieson and Allendorf.

There are many assertions in Jamieson and Allendorfs recent review in TREE [1] (JA2012) that are either incorrect, or contradict current knowledge, the material they cite (especially [2–4]), or their own publications [4–6]. Their review also includes contradiction and misrepresentation of published work. Given space and citation constraints, here we only address some key issues, and reference mainly reviews.

Moving beyond the conceptual: specificity in regional climate change adaptation actions for biodiversity in South East Queensland, Australia

While many scientific assessments have been recommending general strategies for biodiversity conservation under climate change, translation of these recommendations into specific actions and practice has been limited. Focusing on two biomes, rainforest and wetlands in biodiverse South East Queensland, Australia, we demonstrate how general principles can be translated into specific actions for stakeholders and responsible agencies. We synthesize research that is contextualizing protection of refugia and habitat connectivity, establishing baseline data sets to detect change and developing strategic conservation planning scenarios to adjust reserve boundaries or situate new reserves. This has been achieved by coupling spatial information on biological assets (i.e. ecosystems and species) with future climate scenarios and process models to anticipate movement of critical habitats. Conservation planning software is also being used to prioritize investment to meet specific objectives. This approach is enabling us to identify at-risk biological assets, opportunities to ameliorate threats and obstacles to delivering regional adaptation actions. A larger total reserved area is needed, with proactive planning to capture areas further inland and along watercourses. Major obstacles include conflict between urbanization and priorities for habitat conservation and the need for greater levels of investment for monitoring programmes and to protect landward shifted wetlands on private land.

Minimum viable population size: not magic, but necessary

We agree with Flather and colleagues that there is no ‘magic number’ or universal threshold around which one can plan for threatened species management to cover all contingencies; neither have we ever claimed so. As Flather and colleagues reiterate, a minimum viable population size [MVP; the abundance above which the probability of extinction (over conservation-relevant timescales) is unacceptably low for any species] is illusory. There is substantial variation in MVP among species and probably across subpopulations for widespread or spatially disjunct species, and there is no obvious ‘decision threshold’, as reviewed by Traill et al. and elsewhere. Yet even with this uncertainty, ignoring MVP because of concerns over its imperfections or risk of misuse, as Flather et al. seem to prefer, would be imprudent.

Satellite telemetry and seasonal movements of Magpie Geese (Anseranas semipalmata) in tropical northern Australia

Abstract Knowledge of the patterns of movement of tropical waterfowl should assist in long-term conservation of these birds and their wetlands. Data that indicate or suggest the extent of connectivity between populations help us to make decisions, particularly when those populations are threatened by loss and fragmentation of habitat. To date, there has been little research on tropical waterfowl, with most work on this group of birds done in temperate regions. We tracked the seasonal movements of 10 Magpie Geese (Anseranas semipalmata) in tropical northern Australia, predominantly within Kakadu National Park, using satellite telemetry. Movements were multi-directional and the maximum linear distance travelled by an individual was 114 km from the site of release, over 38 weeks of tracking. Movements did appear to be related to seasonal environmental fluctuations, with some birds moving to favoured breeding and foraging sites, but most monitored birds were resident within the national park. No accurate data were obtained beyond 12 months, with most birds apparently losing their telemeters within 6 months. Just 62% of point-location data were accurate to within 1000 m. Our work provides further ecological data on a species threatened by sea-level rise and important to Aboriginal and recreational hunters.

How will climate change affect plant–herbivore interactions? A tropical waterbird case study

Abstract We review interactions between waterfowl and wetlands and outline the shifts that are likely to occur within these relationships through global climate change. We highlight the relative paucity of research on populations of tropical waterfowl and their food plants, and use an iconic tropical species of waterfowl, the Magpie Goose (Anseranas semipalmata), as a case study. We provide background on the known and hypothesised interactions between Magpie Geese and wetlands and provide a hypothetical framework of the mechanistic changes to these relationships through climatic change, including rises in sea level, temperature increases, elevated CO2 levels and altered rainfall regimes. Intrusion of saline water through sea-level rise and extended periods of inundation following increased annual rainfall are the two plausible drivers of change in the wetland sedge plants that support Magpie Geese populations. We show how the relative importance of these, and other, threatening factors can be challenged with data from the field and laboratory under multiple working hypotheses. Understanding the imminent shifts in the structure of wetland plant communities and the likely response of waterfowl populations will focus management on key threats and critical habitat. This includes identification of important wetlands and the construction of buffers at them to slow salt-water intrusion.

Rainfall and temperature variation does not explain arid species diversity in outback Australia

Steps toward conserving biodiversity should start at understanding the components across spatial scales and a determination of the drivers of these. Here we determine additive species diversity for arid South Australia, based on over 50 years of survey data. Elevation and soil data were sourced through the Australian Government, and climate data from the WorldClim database. Alternative hypotheses relating the effect of climatic and environmental parameters to diversity were tested using generalized linear models and ranked according to information-theoretic statistics. Total species richness for the region was 1824, similar to all arid regions. α-diversity values were low, relative to the contributions made by β-diversity toward total γ-diversity, similar to additive diversity indices for nonarid biomes. There was a lack of statistical support for our hypothesis that regional spatial variation in arid region diversity can be explained by climate topography. Arid South Australian species diversity appears to be largely driven by environmental parameters at the localized scale – beyond the resolution of available survey data. Heterogeneity in habitat, provided by mountainous regions, likely contributes toward the high β-diversity values. Our research is the first application of the additive (not multiplicative) approach toward understanding diversity within arid Australia.

An aggregative response of the tropical Australian magpie goose (Anseranas semipalmata) to seasonal floodplains

We describe the spatial aggregation of the magpie goose (Anseranas semipalmata) in relation to the dynamics of the ephemeral floodplains of northern Australia. Past broad-scale studies have linked geese to floodplains dominated by the sedge, Eleocharis dulcis, but the type of response has not been determined, nor the impact of predation on food plants. Moreover, departure thresholds are not known. We develop hypotheses on aggregation and departure and confront these with field data. Thus, from 2005–2007 we established two sites on the floodplains of Kakadu National Park (three 1-ha plots per site, six plots in total) and used for monthly, dry season bird counts. An airboat was used to collect data from each of the six plots, including sedge tubers and measures of water level and soil viscosity. Further, we built exclosures (three per site, six in total) to test the impact of herbivory on E. dulcis. Generalized linear models and information theory were used to test the strength of supporting evidence for alternate hypotheses. Geese showed a clear aggregative response to E. dulcis tubers, were forced to depart following floodplain drying and had a marked impact on E. dulcis tuber density. Despite this, there was no evidence of a negative-feedback mechanism between plant–herbivore populations, suggesting that the system is driven by extrinsic parameters (here rainfall).