Determinants of intra‐annual population dynamics in a tropical soil arthropod

Abstract

Studies on inter‐annual dynamics of populations from temperate regions have shown that density dependence and climate effects are relatively common, albeit weak. Yet, for short‐lived organisms, intra‐annual variation may be at least as important. Furthermore, tropical species commonly experience temperatures close to their upper thermal limit and thus may be more likely to experience heat stress. Here, we used the soil mite Rostrozetes ovulum to investigate the drivers of intra‐annual population dynamics in an Amazonian rain forest. We sampled 3,600 soil cores from 20 transects during 13 months, obtaining 180 mite counts. Next, we built a dynamic N‐mixture model accounting for different detection probabilities between soil types. In a Bayesian framework, we used this model to estimate (a) the strength of density dependence and (b) per capita growth rates, which were then tested against environmental variables. We found that the intra‐annual population dynamics of R. ovulum were weakly density dependent. Further, per capita growth rates increased with resource supply (litterfall) and decreased with maximum temperature over much of the observed thermal range, although these effects explained relatively little variance. Yet, the seasonal correlation between these factors created a trade‐off, so that realized population growth was highest when neither resource supply nor thermal suitability was optimal. Overall, our results suggest that the mechanisms shaping soil animal population dynamics may be surprisingly similar across latitudes. Our model offers a starting point for analyses of soil animal counts when extraction from soil samples is imperfect.

Geographic distance and vegetation structure rather than river barrier drive ant beta diversity across Central Amazonia

“…Temperature affects ant thermoregulation, shaping thermal niches (Cerdá et al 1998;Cerdá and Retana 2000;Kaspari et al 2019) and also is related to species richness at larger scales (Dunn et al 2009). Indeed, we found that temperature had a direct effect on compositional dissimilarity, corroborating that even the low variation in temperature of the Amazon may affect the physiology of soil arthropods (Pequeno et al 2020). Nevertheless, temperature's greatest effect was indirect, through NDVI (b indirect = 0.74 × 0.36 = 0.27 vs. b direct = 0.17), which had the strongest direct effect among environmental variables (Fig.…”

Hunger for sex: Abundant, heterogeneous resources select for sexual reproduction in the field

“…Litter supply increases oribatid mite populations in tropical forests (Ashford et al, 2013; Pequeno et al, 2020), and thus can be expected to increase the effective population size of species. Therefore, stronger selection for sex with increasing litter amount agrees with linkage‐based advantages of sexual reproduction, which should increase in effectively larger populations (mechanisms 1, 2 and 3 in Table 1).…”

“…Litter supply increases oribatid mite populations in tropical forests (Ashford et al, 2013;Pequeno et al, 2020), and thus can be expected to increase the effective population size of species.…”

“…Our analysis did not consider temporal dynamics, but oribatid mite populations fluctuate in size in response to seasonal litterfall (Pequeno et al, 2020). Under temporal variation, selection for sex should still increase with litter amount through linkage-based mechanisms, granted that more resources support a larger (harmonic) mean effective population size over time (Charlesworth, 2009).…”

Microhabitat Selection and Population Density of Nehalennia Speciosa Charpentier, 1840 (Odonata: Coenagrionidae) in a Peripheral Microrefugium

“…Nevertheless, they have been mainly applied to vertebrates (e.g. Waddle et al 2015;Hamilton et al 2019) and rarely to invertebrate species (Klarenberg and Wisely 2019;Pequeno et al 2020).…”