Model-based approaches to understanding wild meat harvesting in Central Africa: uncertainty, yields and ecosystem impacts

The current levels of bushmeat harvesting, combined with other human-made pressures, are likely to drive many African species to extinction and disrupt ecological processes. However, reliably predicting what the appropriate harvesting levels might be is a challenge. Existing methods for assessing sustainability of harvesting rely heavily on species observational data, despite the widely-recognised limitations (such as geographical and taxonomic biases) of these data. In addition, population models can be employed; however, these necessitate parameter estimates which are often lacking. This thesis investigates new model-based approaches to overcoming these data and modelling limitations, in particular, high parameter uncertainty and simplistic population models which ignore many of ecological complexities (such as multi-trophic interactions). The first two chapters investigate proportional and quota-based harvesting in single-species population models of duiker antelope, but extended to include (1) an explicit consideration of parameter uncertainty, which revealed a trade-off between yield and population survival probability not apparent when ignoring uncertainty; and (2) model-based adaptive harvesting, which was predicted to increase yields and survival, particularly when combined with parameter updating. Chapters 3 and 4 employ the Madingley General Ecosystem Model, which can simulate a wide range of scenarios without any species-specific data. The Madingley Model predictions for duiker harvesting were similar to those from the single-species model, but the Madingley could also predict (1) wider ecosystem impacts of duiker harvesting (which were minimal); (2) yields and impacts for multiple species harvesting (both yields and impacts were greater than for duiker, with large reductions in target functional groups and increases in smaller-bodied animals); and (3) variation in yield and impacts among ecosystems (yields varied by a factor of ten; impacts varied quantitatively, but not qualitatively). These findings highlight the potential value of model-based approaches for informing bushmeat harvesting policies, given existing limitations in data and systems understanding

A manifesto for predictive conservation

If efforts to tackle biodiversity loss and its impact on human wellbeing are to be successful, conservation must learn from other fields which use predictive methods to foresee shocks and pre-empt their impacts in the face of uncertainty, such as military studies, public health and finance. Despite a long history of using predictive models to understand the dynamics of ecological systems and human disturbance, conservationists do not systematically apply predictive approaches when designing and implementing behavioural interventions. This is an important omission because human behaviour is the underlying cause of current widespread biodiversity loss. Here, we critically assess how predictive approaches can transform the way conservation scientists and practitioners plan for and implement social and behavioural change among people living with wildlife. Our manifesto for predictive conservation recognises that social-ecological systems are dynamic, uncertain and complex, and calls on conservationists to embrace the forward-thinking approach which effective conservation requires

Images as proximity sensors : the incidence of conspecific foraging in Antarctic fur seals

Background: Although there have been recent advances in the development of animal-attached ‘proximity’ tags to remotely record the interactions of multiple individuals, the efficacy of these devices depends on the instrumentation of sufficient animals that subsequently have spatial interactions. Among densely colonial mammals such as fur seals, this remains logistically difficult, and interactions between animals during foraging have not previously been recorded. Results: We collected data on conspecific interactions during diving at sea using still image and video cameras deployed on 23 Antarctic fur seals. Animals carried cameras for a total of 152 days, collecting 38,098 images and 369 movies (total time 7.35 h). Other fur seals were detected in 74% of deployments, with a maximum of five seals seen at one time (n = 122 images, 28 videos). No predators other than conspecifics were observed. Detection was primarily limited by light conditions, since conspecifics were usually further from each other than the 1-m range illuminated by camera flash under low light levels. Other seals were recorded at a range of depths (average 27 ± 14.3 m, max 66 m). In terms of bouts of dives, still images of other seals were recorded in 5 single dives (of 330) and 28 bouts of dives <2 min apart (of 187). Linear mixed models suggested a relationship between conspecific observations per dive and the number of krill images recorded per dive. Using light conditions as a proxy for detectability, other seals were more likely to be observed at the bottom of dives than during descent or ascent. Seals were also more likely to be closer to each other and oriented perpendicular to each other at the bottom of dives, and in the same direction as each other during ascent. Conclusions: These results are contrary to animal-attached camera observations of penguin foraging, suggesting differing group-foraging tactics for these marine predators. Group foraging could have consequences for models linking predator behaviour to prey field densities since this relationship may be affected by the presence of multiple predators at the same patch.Publisher PDFPeer reviewe

Modelling parameter uncertainty reveals bushmeat yields versus survival trade-offs in heavily-hunted duiker Cephalophus spp.

Reliably predicting sustainable exploitation levels for many tropical species subject to hunting remains a difficult task, largely because of the inherent uncertainty associated with estimating parameters related to both population dynamics and hunting pressure. Here, we investigate a modelling approach to support decisions in bushmeat management which explicitly considers parameter uncertainty. We apply the approach to duiker Cephalophus spp., assuming either a constant quota-based, or a constant proportional harvesting, strategy. Within each strategy, we evaluate different hunting levels in terms of both average yield and survival probability, over different time horizons. Under quota-based harvesting, considering uncertainty revealed a trade-off between yield and extinction probability that was not evident when ignoring uncertainty. The highest yield was returned by a quota that implied a 40% extinction risk, whereas limiting extinction risk to 10% reduced yield by 50%-70%. By contrast, under proportional harvesting, there was no trade-off between yield and extinction probability. The maximum proportion returned a yield comparable with the maximum possible under quota-based harvesting, but with extinction risk below 10%. However, proportional harvesting can be harder to implement in practice because it depends on an estimate of population size. In both harvesting approaches, predicted yields were highly right-skewed with median yields differing from mean yields, implying that decision outcomes depend on attitude to risk. The analysis shows how an explicit consideration of all available information, including uncertainty, can, as part of a wider process involving multiple stakeholders, help inform harvesting policies

High pathogenicity avian influenza (H5N1) in northern gannets: global spread, clinical signs, and demographic consequences

During 2021 and 2022 High Pathogenicity Avian Influenza (HPAI) killed thousands of wild birds across Europe and North America, suggesting a change in infection dynamics and a shift to new hosts, including seabirds. Northern Gannets (Morus bassanus) appeared especially severely impacted, but a detailed account of the data available is required to help understand how the virus spread across the metapopulation, and the ensuing demographic consequences. Accordingly, we analyse information on confirmed and suspected HPAIV outbreaks across most North Atlantic Gannet colonies and for the largest colony (Bass Rock, UK), provide impacts on population size, breeding success, and preliminary results on apparent adult survival and serology. Unusually high numbers of dead Gannets were first noted at colonies in Iceland during April 2022. Outbreaks in May occurred in many Scottish colonies, followed by colonies in Canada, Germany and Norway. By the end of June, outbreaks had occurred in colonies in Canada and the English Channel. Outbreaks in 12 UK and Ireland colonies appeared to follow a clockwise pattern with the last infected colonies recorded in late August/September. Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead birds testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied nest sites decreased by at least 71%, breeding success declined by ~66% compared to the long-term UK mean and the resighting of marked individuals suggested that apparent adult survival between 2021 and 2022 could have been substantially lower than the preceding 10-year average. Serological investigation detected antibodies specific to H5 in apparently healthy birds indicating that some Gannets recover from HPAIV infection. Further, most of these recovered birds had black irises, suggestive of a phenotypic indicator of previous infection. Untangling the impacts of HPAIV infection from other challenges faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations as the likelihood of further epizootics increases, due to increasing habitat loss and the industrialization of poultry production