DOI: 10.5061/dryad.z08kprrjf
title: Age specific impacts of vegetation functional traits on gastro-intestinal nematode parasite burdens in a large herbivore

description: Gastro-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 is important in
 wildlife systems, but the environmental drivers underlying this variation
 remain poorly understood. We 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 individual’s 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.  Effects 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. In 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. Our findings
 support the importance of fine-scale environmental variation for wildlife
 disease ecology and provide 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.
description: This dataset consists of long-term field data and samples
 collected by St Kilda research teams between 1988 and 2017, and calculated
 vegetation functional traits based on vegetation surveys of the island
 between 2008 and 2012. We used census data from the full year to calculate
 home ranges and strongyle faecal egg counts (FEC) and weight from the
 August catch each year.   
 Ten study area censuses of the Soay sheep population are
 conducted during spring, summer, and autumn, and the location of each
 sheep is noted (resulting in 30 censuses a year). A home range calculation
 was run on these sightings, resulting in a home range for each individual
 per year. Vegetation trait values for each species were obtained from the
 LEDA TraitBase and Ellenberg values and a sheep's average value for
 vegetation traits was determined by community-weighted means within its
 home range.    In August,
 sheep are captured and morphometric measurements/faecal samples are
 collected. Gastrointestinal nematode eggs were counted using a modified
 McMaster technique. Due to difficulty distinguishing species, the number
 of eggs of five main nematode species was included as one measurement
 (FEC). Individual faecal samples were associated with an individual's
 averaged census location for INLA spatiotemporal modelling.