Biology subjects

Pakeman, R. J.

Publications and source records attributed to Pakeman, R. J..

5 recordsLinked to original sources

bioRxiv2026

The impacts of grazing pressure by large herbivores on short-tailed field vole (Microtus agrestis) population cycles: results from a long-term upland experiment

Understanding how large herbivores influence cyclic small-mammal populations is essential for predicting community dynamics in grazed ecosystems. Using a 23-year upland grazing experiment in Scotland, United Kingdom, we test how varying livestock grazing pressures affect population cycles of the short-tailed field vole Microtus agrestis, a keystone herbivore and prey species of birds of conservation concern. We combined long-term vole sign indices (VSI), vegetation surveys, climate data and used wavelet analyses and mixed-effects models to quantify changes in VSI (a proxy for abundance), cycle amplitude and periodicity across four grazing treatments and three spatial blocks. Vole abundance and cycle amplitude declined with increasing grazing pressure, yet the frequency of vole population oscillations remained strikingly consistent across all treatments, with a dominant ~3.5-year cycle persisting throughout most of the study. Ungrazed plots supported the highest mean VSI and the largest amplitude oscillations. We found a pronounced, spatially-restricted cycle collapse occurred between 2009-2016 in one experimental block. This breakdown coincided with unusually cold winters and lower vegetation density, suggesting that local microclimate and habitat structure interact to destabilise vole cycles. Vegetation density (but not height) predicted VSI in the more intensively grazed treatments, indicating that grazing-driven changes in habitat structure indirectly mediate vole dynamics. Our findings demonstrate that large herbivores can substantially modify vole population dynamics through both direct and indirect pathways, altering cycle amplitude, habitat suitability and resilience to climatic perturbations. These results highlight the need to consider interactions between grazing, vegetation structure and climate variability when predicting small-mammal population dynamics and their cascading ecological effects.

ecology↗

bioRxiv2023

Age specific impacts of vegetation functional traits on gastro-intestinal nematode parasite burdens in a large herbivore

O_LIGastro-intestinal nematode (GIN) parasites play an important role in the ecological dynamics of many animal populations. Recent studies suggest fine-scale spatial variation in GIN infection dynamics are important in wildlife systems, but the environmental drivers underlying this variation remain poorly understood. C_LIO_LIWe used data from over two decades of GIN parasite egg counts, host space use, and spatial vegetation data from a long-term study of Soay sheep on St Kilda to test how spatial autocorrelation and vegetation in an individuals home range predict parasite burden across three age groups. We developed a novel approach to quantify the plant functional traits present in a home range to describe the quality of vegetation present. C_LIO_LIEffects of space and vegetation varied between age classes. In immature lambs, strongyle parasite faecal egg counts (FEC) were spatially structured, being highest in the north and south of our study area. Independent of host body weight and spatial autocorrelation, plant functional traits predicted parasite egg counts. Higher egg counts were associated with more digestible and preferred plant functional traits, suggesting the association could be driven by host density and habitat preference. C_LIO_LIIn contrast, we found no evidence that parasite FEC were related to plant functional traits in the host home range in yearlings or adult sheep. Adult FEC were spatially structured, with highest burdens in the north-east of our study area, while yearling FEC showed no evidence of spatial structuring. C_LIO_LIOur findings support the importance of fine-scale environmental variation for wildlife disease ecology and provides new evidence that such effects may vary across demographic groups within a population. Parasite burdens in immature individuals appear more readily influenced by fine-scale spatial variation in the environment, highlighting the importance of such heterogeneity for our understanding of wildlife epidemiology and health. C_LI

ecology↗

bioRxiv2022

Functional traits trade-offs define plant population stability worldwide

O_LIEcological theory posits that temporal stability patterns in plant populations are associated with differences in species ecological strategies. However, empirical evidence is lacking about which traits, or trade-offs, underlie species stability, specially across different ecosystems. C_LIO_LITo address this, we compiled a global collection of long-term permanent vegetation records (>7000 plots from 78 datasets) from a wide range of habitats and combined this with existing trait databases. We tested whether the observed inter-annual variability in species abundance (coefficient of variation) was related to multiple individual traits and multivariate axes of trait variations (PCoA axes). C_LIO_LIWe found that species with greater leaf dry matter content and seed mass were consistently more stable over time (lower variability in species abundance) although other leaf traits played a significant role as well, albeit weaker. Using multivariate axes did not improve predictions by specific traits. C_LIO_LIOur results confirm existing theory, providing compelling empirical evidence on the importance of specific traits, which point at ecological trade-offs in different resource use and dispersal strategies, on the stability of plant populations worldwide. C_LI

ecology↗

bioRxiv2022

Long-term temporal trends in gastrointestinal parasite infection in wild Soay sheep

Monitoring the prevalence and abundance of parasites over time is important for addressing their potential impact on host life-histories, immunological profiles, and their influence as a selective force. Only long-term ecological studies have the potential to shed light on both the temporal trends in infection prevalence and abundance and the drivers of such trends, because of their ability to dissect drivers that may be confounded over shorter time scales. Despite this, only a relatively small number of such studies exist. Here, we analysed changes in the prevalence and abundance of gastrointestinal parasites in the wild Soay sheep population of St Kilda across 31 years. The host population density has increased across the study, and population density is known to increase parasite transmission, but we found that density and year explained temporal variation in parasite prevalence and abundance independently. Prevalence of both strongyle nematodes and coccidian microparasites increased during the study, and this effect varied between lambs, yearlings and adults. Meanwhile, abundance of strongyles was more strongly linked to host density than to temporal (yearly) dynamics, while abundance of coccidia showed a strong temporal trend without any influence of density. Strikingly, coccidian abundance increased threefold across the course of the study in lambs, while increases in yearlings and adults were negligible. Our decades-long, intensive, individual-based study will enable the role of environmental change and selection pressures in driving these dynamics to be determined, potentially providing unparalleled insight into the drivers of temporal variation in parasite dynamics in the wild. Key findingsO_LIWe studied temporal trends in gastrointestinal parasites of wild sheep over 31 years C_LIO_LIYear and host population density explained temporal variation in parasites independently C_LIO_LIPrevalence of both strongyle nematodes and coccidia varied across the study period C_LIO_LIAbundance of strongyles was more closely linked to host density than year C_LIO_LIAbundance of coccidia increased threefold over time in lambs, but did not vary in adults C_LI

ecology↗

bioRxiv2021

LOTVS: a global collection of permanent vegetation plots

Analysing temporal patterns in plant communities is extremely important to quantify the extent and the consequences of ecological changes, especially considering the current biodiversity crisis. Long-term data collected through the regular sampling of permanent plots represent the most accurate resource to study ecological succession, analyse the stability of a community over time and understand the mechanisms driving vegetation change. We hereby present the LOng-Term Vegetation Sampling (LOTVS) initiative, a global collection of vegetation time-series derived from the regular monitoring of vascular plants in permanent plots. With 79 datasets from five continents and 7789 vegetation time-series monitored for at least six years and mostly on an annual basis, LOTVS possibly represents the largest collection of temporally fine-grained vegetation time-series derived from permanent plots and made accessible to the research community. As such, it has an outstanding potential to support innovative research in the fields of vegetation science, plant ecology and temporal ecology.

ecology↗