Non‐invasive physiological markers demonstrate link between habitat quality, adult sex ratio and poor population growth rate in a vulnerable species, the Cape mountain zebra

Abstract

Abstract1. Effective conservation and species management require an understanding of the causes of poor population growth. Conservation physiology uses biomarkers to identify factors that contribute to low individual fitness and population declines.Building on this, macrophysiology can use the same markers to assess how individual physiology varies with different ecological or demographic factors over large temporal and spatial scales.2. Here, we use a macrophysiological approach to identify the ecological and demographic correlates of poor population growth rates in the Cape mountain zebra metapopulation. We use two non-invasive biomarkers: faecal glucocorticoids as a measure of chronic stress, and faecal androgens as an indicator of male physiological status.3. We found that faecal glucocorticoid concentrations were highest in the spring prior to summer rainfall, and were elevated in individuals from populations associated with lowquality habitat (lower grass abundance). In addition, faecal androgen concentrations were higher in populations with a high proportion of non-breeding stallions (where male:female adult sex ratios exceed 2:1) suggesting sex ratio imbalances may intensify male competition. Finally, population growth rate was negatively associated with faecal glucocorticoid concentrations and female fecundity was negatively associated with faecal androgens, indicating a relationship between hormone profiles and fitness.4. Together, our results provide cross-population evidence for how poor population growth rates in Cape mountain zebra can be linked to individual physiological biomarkers. More broadly, we advocate physiological biomarkers as indicators of population viability, and as a way to evaluate the impact of variable ecological and demographic factors. In addition, conservation physiology can be used to assess the efficacy of management interventions for this subspecies, and this approach could inform models of species' responses to future environmental change. K E Y W O R D Sandrogens, conservation management, faecal hormone metabolites, glucocorticoids, habitat quality, macrophysiology, sex ratio skewThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Glucocorticoids link forest type to local abundance in tropical birds

“…For example, poor body condition in snowshoe hare Lepus americanus (Boonstra & Singleton, 1993) and marine iguanas Amblyrhynchus cristatus (Romero & Wikelski, 2001) was associated with higher stress levels and with poorer survival perspectives. Similarly, Lea et al (2018) found that cape mountain zebras Equus zebra zebra living in relatively lower quality habitat had highest faecal glucocorticoid concentrations, which were negatively correlated with long-term population growth and female fecundity. One possible explanation of the association between glucocorticoids and relative population abundance might lie with energy budget as survival probability decreases in individuals whose stress levels cause long-term energy needs that exceed energy intake (McEwen & Wingfield, 2003).…”

Suitability and Transferability of the Resource-Based Habitat Concept: A Test With an Assemblage of Butterflies

“…Habitat quality (from resource composition and availability) predicted density or population size in the Great Crested Newt Triturus cristatus (Unglaub et al, 2018) and the Grizzly bear Ursus arctos (Lamb et al, 2018). In the Cap mountain zebra Equus zebra zebra, lower resource availability influenced individual physiology, in turn affecting population growth rate (Lea et al, 2018). In the mud crab Panopeus herbstii, habitat quality (reef height, in the field) and the diet (in the lab) impacted on the reproductive performance of females (Griffen and Norelli, 2015).…”

Macrophysiology as a powerful tool for evaluating metapopulation stress and the effectiveness of conservation actions

“…Lea et al. 's study () is important because it convincingly demonstrates how a non‐invasive macrophysiological approach can be used at a metapopulation scale to evaluate on‐going conservation strategies. Although the exact causes relating higher androgen levels in males to low female fecundity and poor population performance in the Cape mountain zebra remain to be determined (e.g.…”

“…In a new study, Lea et al (2018) use a macrophysiology approach to identify potential causes of poor population growth in a vulnerable species, the Cape mountain zebra (Equus zebra zebra) (Ripple et al, 2015). Macrophysiology is the investigation of physiological trait variations over large geographical and temporal scales and the ecological implications of these variations (Chown, Gaston, & Robinson, 2004).…”

“…Functional Ecology VIBLANC the Cape mountain zebra as a partial refugee species (Lea, Kerley, Hrabar, Barry, & Shultz, 2016). Lea et al (2018) use non-invasive measurements of fecal glucocorticoids and fecal androgens across seven South African conservation reserves combined with knowledge on habitat (palatable grass abundance, microclimate) and social group composition (size and sex ratio) within each reserve to explore potential causes of uneven performance of Cape mountain zebra populations across reserves. They show that zebra baseline stress levels (fecal glucocorticoids) are generally more elevated in habitats with low grass abundance and are negatively associated with female fecundity and long-term population growth across habitats.…”