The effect of elevation and time on mountain spider diversity: a view of two aspects in the Cederberg mountains of South Africa

Abstract

Aim Our aim is to test if long-term patterns in a alpha and b beta diversity along an elevational transect on two aspects of a mountain are consistent through time using spiders as model organisms, quantify the role of elevation and time (seasonal and inter-annual) in explaining these patterns and partition the relative contribution of nestedness, species turnover and species loss in explaining these diversity patterns.Location The transect is across the Cederberg mountains in the Cape Floristic Kingdom, Western Cape, South Africa and is constituted by 17 sites with an elevational range of 1900 m on two aspects of the mountain (east and west).Methods Spider assemblages were sampled biannually (wet and dry seasons) over 6 years. Four replicates per site, each consisting of a 5 9 2 pitfall grid, were sampled for 5 days sessions. Generalized linear mixed models with Poisson error structure for species richness (alpha diversity), binomial error structure for beta diversity (Jaccard dissimilarity b cc and its partitioned components, b -3 and b rich ), and Gaussian error structure for beta diversity values standardized by a null model (SES) were used to model the effects of elevation and season on these two indices respectively.Results Although varying considerably between years, spider alpha diversity had a hump-shaped pattern on the western aspect and U-shaped on the eastern aspect. However, season interacted with elevation to produce more complex patterns during the dry season. There was no significant nestedness except for two instances on the western aspect. Replacement accounted for 60-70% of beta diversity between sites, and elevational distance decay in beta diversity was the result of increased turnover on the western aspect and increased species loss on the eastern aspect. Standardized patterns suggest that there are no effects of season on beta diversity except for a decreased distance decay during the dry season on the western aspect.Main conclusions Large-scale predictors of spider alpha diversity explained small amounts of variation in spider diversity, pointing to the importance of local and stochastic processes. Regional turnover of spider diversity is mainly the result of niche processes, suggesting localized adaptation of taxa, further supported by the lack of nestedness in assemblages.

Seasonal shifts of biodiversity patterns and species’ elevation ranges of butterflies and moths along a complete rainforest elevational gradient on Mount Cameroon

“…Any more general conclusions are impeded yet because any comparably comprehensive datasets from the tropics are lacking. However, two studies of seasonal shifts of arthropod diversity on subtropical mountains in southern Africa are consistent with our results; an upward shift of diversity peaks was unveiled in a multiple‐year study of ants (Bishop et al, ), as well as in a study of spiders (Foord & Dippenaar‐Schoeman, ). In the latter, a different pattern of the spider diversity shift was detected among the two studied slopes with different precipitation regimes (Foord & Dippenaar‐Schoeman, ).…”

“…However, two studies of seasonal shifts of arthropod diversity on subtropical mountains in southern Africa are consistent with our results; an upward shift of diversity peaks was unveiled in a multiple‐year study of ants (Bishop et al, ), as well as in a study of spiders (Foord & Dippenaar‐Schoeman, ). In the latter, a different pattern of the spider diversity shift was detected among the two studied slopes with different precipitation regimes (Foord & Dippenaar‐Schoeman, ). Additionally, Meyer et al () revealed seasonal differences in ground‐dwelling arthropod communities along an elevational gradient in the subtropical southwestern US but did not further dissect their patterns or drivers.…”

Altitudinal gradient in species richness and composition of dung beetles (Coleoptera: Scarabaeidae) in an eastern Euro-Mediterranean locality: Functional, seasonal and habitat influences

“…Thus, the interplay between local climatic conditions (mainly temperature) and evolutionary conserved preferences of species (Wiens & Graham, 2005;Merckx et al, 2015) seem to explain current seasonal and altitudinal gradients, as well as contributing to an understanding of the relative occurrence of Aphodiinae and Scarabaeinae (Lobo, 1997). However, the general bimodal pattern was not only recorded when the seasonal responses of the different groups were analysed separately, but also when the specifi c seasonal pattern at each locality was examined as is recorded in other studies (Jay-Robert et al, 2008;Foord & Dippenaar-Schoeman, 2016).This indicates that these altitudinal patterns are deeply affected by the interplay between the climatic factors infl uencing all insect development stages and the thermal and hydric preferences of species. These results may also indicate that the most stressful periods impose a severe environmental constraint on those species unable to maintain viable populations throughout the entire year at a site because the favourable period shortens with increasing altitude.…”

Seasonal variation in a diverse beetle assemblage along two elevational gradients in the Australian Wet Tropics

“…Temporal patterns of abundance and diversity that reflect changing seasonal climatic conditions are frequently ignored in tropical rainforests 13 . Patterns of seasonality among invertebrates in particular are poorly understood, with a few notable exceptions 11 , 12 , 14 – 20 . Wolda 15 used a 14 year dataset of light-trapped insects in Panama to demonstrate that populations of insects change both within and between years.…”