ORCID Profile
0000-0001-7477-2642
Current Organisation
University of Zurich
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Publisher: Wiley
Date: 18-09-2019
Abstract: Environmental change can impact the stability of ecological systems and cause rapid declines in populations. Abundance-based early warning signals have been shown to precede such declines, but detection prior to wild population collapses has had limited success, leading to the development of warning signals based on shifts in distribution of fitness-related traits such as body size. The dynamics of population abundances and traits in response to external environmental perturbations are controlled by a range of underlying factors such as reproductive rate, genetic variation and plasticity. However, it remains unknown how such ecological and evolutionary factors affect the stability landscape of populations and the detectability of abundance and trait-based early warning signals. Here, we apply a trait-based demographic approach and investigate both trait and population dynamics in response to gradual and increasing changes in the environment. We explore a range of ecological and evolutionary constraints under which stability of a population may be affected. We show both analytically and with simulations that strength of abundance- and trait-based warning signals are affected by ecological and evolutionary factors. Finally, we show that combining trait- and abundance-based information improves our ability to predict population declines. Our study suggests that the inclusion of trait dynamic information alongside generic warning signals should provide more accurate forecasts of the future state of biological systems.
Publisher: Wiley
Date: 25-01-2021
DOI: 10.1111/ELE.13681
Abstract: When facing an emerging infectious disease of conservation concern, we often have little information on the nature of the host‐parasite interaction to inform management decisions. However, it is becoming increasingly clear that the life‐history strategies of host species can be predictive of in idual‐ and population‐level responses to infectious disease, even without detailed knowledge on the specifics of the host‐parasite interaction. Here, we argue that a deeper integration of life‐history theory into disease ecology is timely and necessary to improve our capacity to understand, predict and mitigate the impact of endemic and emerging infectious diseases in wild populations. Using wild vertebrates as an ex le, we show that host life‐history characteristics influence host responses to parasitism at different levels of organisation, from in iduals to communities. We also highlight knowledge gaps and future directions for the study of life‐history and host responses to parasitism. We conclude by illustrating how this theoretical insight can inform the monitoring and control of infectious diseases in wildlife.
Publisher: The Royal Society
Date: 10-02-2021
Abstract: Studies increasingly show that social connectedness plays a key role in determining survival, in addition to natural and anthropogenic environmental factors. Few studies, however, integrated social, non-social and demographic data to elucidate what components of an animal's socio-ecological environment are most important to their survival. Female giraffes ( Giraffa camelopardalis ) form structured societies with highly dynamic group membership but stable long-term associations. We examined the relative contributions of sociability (relationship strength, gregariousness and betweenness), together with those of the natural (food sources and vegetation types) and anthropogenic environment (distance from human settlements), to adult female giraffe survival. We tested predictions about the influence of sociability and natural and human factors at two social levels: the in idual and the social community. Survival was primarily driven by in idual- rather than community-level social factors. Gregariousness (the number of other females each in idual was observed with on average) was most important in explaining variation in female adult survival, more than other social traits and any natural or anthropogenic environmental factors. For adult female giraffes, grouping with more other females, even as group membership frequently changes, is correlated with better survival, and this sociability appears to be more important than several attributes of their non-social environment.
Publisher: Springer Science and Business Media LLC
Date: 24-03-2016
DOI: 10.1038/NCOMMS10984
Abstract: Foreseeing population collapse is an on-going target in ecology, and this has led to the development of early warning signals based on expected changes in leading indicators before a bifurcation. Such signals have been sought for in abundance time-series data on a population of interest, with varying degrees of success. Here we move beyond these established methods by including parallel time-series data of abundance and fitness-related trait dynamics. Using data from a microcosm experiment, we show that including information on the dynamics of phenotypic traits such as body size into composite early warning indices can produce more accurate inferences of whether a population is approaching a critical transition than using abundance time-series alone. By including fitness-related trait information alongside traditional abundance-based early warning signals in a single metric of risk, our generalizable approach provides a powerful new way to assess what populations may be on the verge of collapse.
Publisher: Proceedings of the National Academy of Sciences
Date: 14-10-2021
Abstract: Disentangling the effects of rainfall timing and magnitude on animal and plant populations is essential to reveal the biological consequence of erse climate change scenarios around the world. We conducted a 10-y, large-scale, manipulative experiment to examine the bottom-up effects of changes in rainfall regime on the population dynamics of Brandt’s voles in the steppe grassland of Inner Mongolia, China. We found that a moderate rainfall increase during the early growing season could produce marked increases in vole population size by increasing the biomass of preferred plant species, whereas large increases in rainfall produced no additional increase in vole population growth. Our study highlights the importance of rainfall magnitude and timing on the nonlinear population dynamics of herbivores.
Publisher: University of Chicago Press
Date: 07-2015
DOI: 10.1086/681573
Abstract: The recent description of potentially generic early warning signals is a promising development that may help conservationists to anticipate a population's collapse prior to its occurrence. So far, the majority of such warning signals documented have been in highly controlled laboratory systems or in theoretical models. Data from wild populations, however, are typically restricted both temporally and spatially due to limited monitoring resources and intrinsic ecological heterogeneity-limitations that may affect the detectability of generic early warning signals, as they add additional stochasticity to population abundance estimates. Consequently, spatial and temporal subs ling may serve to either muffle or magnify early warning signals. Using a combination of theoretical models and analysis of experimental data, we evaluate the extent to which statistical warning signs are robust to data corruption.
Publisher: Wiley
Date: 06-04-2021
Abstract: Approximately 25% of mammals are currently threatened with extinction, a risk that is lified under climate change. Species persistence under climate change is determined by the combined effects of climatic factors on multiple demographic rates (survival, development and reproduction), and hence, population dynamics. Thus, to quantify which species and regions on Earth are most vulnerable to climate‐driven extinction, a global understanding of how different demographic rates respond to climate is urgently needed. Here, we perform a systematic review of literature on demographic responses to climate, focusing on terrestrial mammals, for which extensive demographic data are available. To assess the full spectrum of responses, we synthesize information from studies that quantitatively link climate to multiple demographic rates. We find only 106 such studies, corresponding to 87 mammal species. These 87 species constitute % of all terrestrial mammals. Our synthesis reveals a strong mismatch between the locations of demographic studies and the regions and taxa currently recognized as most vulnerable to climate change. Surprisingly, for most mammals and regions sensitive to climate change, holistic demographic responses to climate remain unknown. At the same time, we reveal that filling this knowledge gap is critical as the effects of climate change will operate via complex demographic mechanisms: a vast majority of mammal populations display projected increases in some demographic rates but declines in others, often depending on the specific environmental context, complicating simple projections of population fates. Assessments of population viability under climate change are in critical need to gather data that account for multiple demographic responses, and coordinated actions to assess demography holistically should be prioritized for mammals and other taxa.
Publisher: Wiley
Date: 08-06-2020
Publisher: Wiley
Date: 08-04-2021
DOI: 10.1002/JWMG.22044
Abstract: Populations are typically defined as spatially contiguous sets of in iduals, but large populations of social species can be composed of discrete social communities that often overlap in space. Masai giraffes ( Giraffa camelopardalis tippelskirchi ) of Tanzania live in distinct social subpopulations that overlap spatially, enabling us to simultaneously explore environmental and social factors correlated with demographic variation in a metapopulation of ,400 adult females and calves. We considered statistically distinct communities in the social network as subpopulations and tested for variation among the 10 subpopulations in adult female survival, calf survival, and reproductive rate (calf‐to‐adult female ratio). We then related variation in demographic rates among subpopulations to differences in vegetation, soil type, proximity to 2 types of human settlements, local giraffe population density, and social metrics of relationship strength and exclusivity among adult females. We did not find any among‐subpopulation effects on adult female survival, suggesting adult female survival is buffered against environmental heterogeneity among subpopulations. Variation in calf demographic rates among subpopulations were correlated with vegetation, soils, anthropogenic factors, and giraffe population density but not with adult female relationship metrics, despite substantial spatial overlap. Subpopulations with more dense bushlands in their ranges had lower calf survival probabilities, and those closer to human settlements had higher reproductive rates, possibly because of spatial gradients in natural predation. Reproductive rates were higher in subpopulations with more volcanic soils, and calf survival probabilities were greater in subpopulations with higher local adult female densities, possibly related to higher‐quality habitat associated with fertile soils or lower predation risk, or to greater competitive ability. The variation in fitness among subpopulations suggests that giraffes do not move unhindered among resource patches to equalize reproductive success, as expected according to an ideal free distribution. The differences in calf survival and reproductive rates could rather indicate intercommunity differences in competitive ability, perception, learning, or experience. Our approach of comparing demography among spatially overlapping yet distinct socially defined subpopulations provides a biologically meaningful way to quantify environmental and social factors influencing fine‐scale demographic variation for social species. © 2021 The Wildlife Society.
Publisher: Wiley
Date: 03-2022
DOI: 10.1002/ECE3.8739
Abstract: Aldabrachelys gigantea (Aldabra giant tortoise) is one of only two giant tortoise species left in the world and survives as a single wild population of over 100,000 in iduals on Aldabra Atoll, Seychelles. Despite this large current population size, the species faces an uncertain future because of its extremely restricted distribution range and high vulnerability to the projected consequences of climate change. Captive‐bred A . gigantea are increasingly used in rewilding programs across the region, where they are introduced to replace extinct giant tortoises in an attempt to functionally resurrect degraded island ecosystems. However, there has been little consideration of the current levels of genetic variation and differentiation within and among the islands on Aldabra. As previous microsatellite studies were inconclusive, we combined low‐coverage and double‐digest restriction‐associated DNA (ddRAD) sequencing to analyze s les from 33 tortoises (11 from each main island). Using 5426 variant sites within the tortoise genome, we detected patterns of within‐island population structure, but no differentiation between the islands. These unexpected results highlight the importance of using genome‐wide genetic markers to capture higher‐resolution genetic structure to inform future management plans, even in a seemingly panmictic population. We show that low‐coverage ddRAD sequencing provides an affordable alternative approach to conservation genomic projects of non‐model species with large genomes.
Publisher: Wiley
Date: 19-09-2021
Abstract: Dispersal is a critical process that shapes the structure of wild animal populations. In species that form multi‐level societies, natal dispersal might be social (associating with a different social community while remaining near the natal area), spatial (moving away from the natal area while continuing to associate with the same community) or both social and spatial (associating with a different community and moving away from the natal area). For such species, classical spatial measures of dispersal, such as distance moved, might not capture social dispersal. We examined dispersal outcomes for 67 male and 70 female giraffe calves over 7 years in a large, unfenced, ecologically heterogeneous landscape. We tested predictions about the influence of sex, food availability, low‐ and high‐impact human settlements, and local giraffe population density on social or spatial dispersal, dispersal distance, and age of dispersal. We found that dispersal is sex‐specific, with females being predominately philopatric. When dispersing, both sexes did so at a mean of 4 years of age. Most (69% of total) young males dispersed, with 84% of male dispersers associating with a different adult female social community than that of their mother, but one in four of these dispersers remained spatially near to their natal area. For adolescent males that dispersed socially but not spatially, overlapping female social communities may represent a potential pool of unrelated mating partners without the risks of travelling to unfamiliar areas. Just 26% of young females dispersed and half of these continued to associate with the adult female social community into which they were born, confirming the importance of maintaining ties among females from calf to adulthood. Furthermore, in iduals born farther from high‐impact human settlements were more likely to spatially or socially‐and‐spatially disperse, move greater distances from their natal areas, and disperse at a younger age. Our study highlights the potential importance of social structure in dispersal decisions, and of tracking social structure when studying dispersal in multi‐level societies, as effective dispersal can be attained without large‐scale spatial displacements.
Publisher: Wiley
Date: 05-10-2016
DOI: 10.1002/ECE3.2531
Publisher: Wiley
Date: 26-07-2021
Abstract: The ability of dispersing in iduals to adjust their behaviour to changing conditions is instrumental in overcoming challenges and reducing dispersal costs, consequently increasing overall dispersal success. Understanding how dispersers' behaviour and physiology change during the dispersal process, and how they differ from resident in iduals, can shed light on the mechanisms by which dispersers increase survival and maximise reproduction. By analysing in idual behaviour and concentrations of faecal glucocorticoid metabolites (fGCM), a stress‐associated biomarker, we sought to identify the proximate causes behind differences in survival and reproduction between dispersing and resident meerkats Suricata suricatta . We used data collected on 67 dispersing and 108 resident females to investigate (a) which in idual, social and environmental factors are correlated to foraging and vigilance, and whether the role of such factors differs among dispersal phases, and between dispersers and residents (b) how time allocated to either foraging or vigilance correlated to survival in dispersers and residents and (c) the link between aggression and change in fGCM concentration, and their relationship with reproductive rates in dispersing groups and resident groups with either long‐established or newly established dominant females. Time allocated to foraging increased across dispersal phases, whereas time allocated to vigilance decreased. Time allocated to foraging and vigilance correlated positively and negatively, respectively, with dispersers' group size. We did not find a group size effect for residents. High proportions of time allocated to foraging correlated with high survival, and more so in dispersers, suggesting that maintaining good physical condition may reduce mortality during dispersal. Furthermore, while subordinate in iduals rarely reproduced in resident groups, the conception rate of subordinates in newly formed dispersing groups was equal to that of their dominant in iduals. Mirroring conception rates, in resident groups, fGCM concentrations were lower in subordinates than in dominants, whereas in disperser groups, fGCM concentrations did not differ between subordinates and dominants. Our results, which highlight the relationship between behavioural and physiological factors and demographic rates, provide insights into some of the mechanisms that in iduals of a cooperative species can use to increase overall dispersal success.
No related grants have been discovered for Arpat Ozgul.