DOI: 10.5061/dryad.5dh98
title: Data from: Climatic conditions cause spatially dynamic polygyny thresholds in a large mammal

description: The polygyny threshold (PT) is a critical transition point in the sexual
 selection process for many organisms in natural populations,
 characterizing when females choose to mate with an already mated male over
 an unmated one to improve fitness. Understanding its causes and
 consequences is therefore of high interest. While both theoretical and
 empirical work suggest that the degree of polygyny within a species is
 plastic and a function of male inequality, the functional relationship
 between underlying availability of resources occupied by breeding males
 under variable climatic conditions and the dynamics of PTs across space
 and time has received less attention. Here, we use a standardized measure
 of male mating inequality as the culmination of female mate choices to
 analyse how spatially dynamic PTs in a naturally regulated feral horse
 (Equus ferus caballus) population emerge along a geographic gradient in a
 known, limiting resource (freshwater) each year from variable climatic
 conditions. Polygyny threshold distance from permanent freshwater
 increased with increasing precipitation during the breeding season of each
 year, suggesting a relationship between annual resource availability and
 female mate choice. The mechanism by which climatic conditions underpin
 the spatial dynamics of PTs was likely through precipitation providing
 ephemeral freshwater sources across the study area that effectively
 weakened the gradient in availability of permanent freshwater, thereby
 providing mating males that occupied home ranges far from permanent water
 with access to this limiting resource and enabling them to attract and
 retain females. Increased precipitation also coincided with a decreased
 proportion of males in the population that experienced sexual selection
 pressure attributed to female mate choice in relation to the acquisition
 and/or defence of freshwater sources. Climatic conditions caused spatial
 shifts in PTs annually along the geographic gradient in resource
 availability. Our findings reveal that such environmental gradients may
 either buffer or amplify impacts of climatic variation on selection
 pressure operating in natural populations, and emphasize the importance of
 integrating spatially explicit PTs with atmospheric fluctuations when
 predicting the effect of climatic change on selection processes within
 populations that occupy environmental gradients.
description: polygyny threshold
 distance data--manning&mcloughinData are from a study of
 spatially explicit counts of feral horses and associated distances to
 nearest permanent freshwater sources on Sable Island, Canada (2008-2013).
 Field Labels Year=year BandStallion=dominant male Sex=gender
 FemaleID=unique female identifier Latitude=latitude Longitude=longitude
 DistH2O_m=distance to nearest permanent freshwater source
 (meters)Female reproduction
 across the polygyny thresholdYear=year
 FemaleDispersion=overdispersed (k&lt;1) or underdispersed (k&gt;1) (see
 methods) FoalsPerFemale=probability that a female would reproduce in that
 group of females binned according to distance from water (see
 methods)Shifts in polygny
 thresholds and male selection pressureYear=year
 NAO_Index=North Atlantic Oscillation Index MeanAdultFemalsPerHarem=mean
 number of females in the harem (geometric mean across January, February,
 and March) AdultSexRatio=number of males ≥4 years old/[males ≥4 years old
 + females ≥2 years old]) from the entire population
 MeanMaximumSummerTemperature_C=mean of daily maximum summer temperatures
 (Celsius) from June through August. TotalSummerPrecipitation_CM=total
 summer precipitation from June through August
 MalePopSegmentUnderCompetition=proportion of the male breeding population
 residing in the region of the island where females were under-dispersed
 (k&gt;1) PropOfYearsUnderMaleSelection=proportion of years where females
 were clustered around particular males (k&gt;1; see methods)
 PolygynyThresholdDistanceFromPond_KM=distance from permanent water where
 k=1 during a given year (see methods)