Descriptive versus explanatory hypotheses in evolutionary research: a potentially concerning bias exemplified by research into the evolution of social organisations in carnivores

Changes in abiotic factors along altitudinal and latitudinal gradients cause powerful environmental gradients. The topography of alpine areas generates environmental gradients over short distances, and alpine areas are expected to experience greater temperature increase compared to the global average. In this study, we investigate alpha, beta, and gamma diversity, as well as community structure, of vascular plant communities along altitudinal gradients at three latitudes in the Swedish mountains. Species richness and evenness decreased with altitude, but the patterns within the altitudinal gradient varied between sites, including a sudden decrease at high altitude, a monotonic decrease, and a unimodal pattern. However, we did not observe a decline in beta diversity with altitude at all sites, and plant communities at all sites were spatially nested according to some other factors than altitude, such as the availability of water or microtopographic position. Moreover, the observed diversity patterns did not follow the latitudinal gradient. We observed a spatial modularity according to altitude, which was consistent across sites. Our results suggest strong influences of site‐specific factors on plant community composition and that such factors partly may override effects from altitudinal and latitudinal environmental variation. Spatial variation of the observed vascular plant communities appears to have been caused by a combination of processes at multiple spatial scales.

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Contrasting altitudinal variation of alpine plant communities along the Swedish mountains

Måsviken

Dalerum

Cousins

2020

“…However, we would like to highlight that this study focuses on quantifying patterns of biodiversity change rather than trying to relate any shifts in biodiversity to potential drivers. We have chosen this approach since we believe that a proper identification of ecological patterns is necessary before any mechanistic hypotheses are developed to test the underlying processes behind such patterns (Dalerum, ). Although intuitive, a monotonic decline in species richness and diversity with increasing altitudes is not generically supported by empirical observations (Colwell & Lees, ).…”

Section: Introductionmentioning

confidence: 99%

Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra

Naud

Måsviken

Freire

et al. 2019

Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.

“…However, since we regarded it to be most germane to first quantify the patterns of spatial variation in ant communities before evaluating potential causes underlying such patterns (Dalerum, 2012), we have here not included any direct correlates to diversity along the gradient, such as soil type, vegetation structure, or grazing pressure.…”

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confidence: 99%

The influence of distance to perennial surface water on ant communities in Mopane woodlands, northern Botswana

Dalerum

Retief

Havemann

et al. 2018

Studies of biodiversity along environmental gradients provide information on how ecological communities change in response to biotic and abiotic factors. For instance, distance to water is associated with several factors that shape the structure and the functioning of ecosystems at a range of spatial scales. We investigated the influence of distance to a perennial water source on ant communities in a semi‐arid savanna in northern Botswana. Ant abundance, taxonomic richness, and both alpha and beta diversity were generally higher during the wet than the dry season. However, there were strong seasonal influences on the effects of distance to water, with more pronounced effects during the wet season. While both abundance and beta diversity declined with increasing distances to water during the wet season, there was a contrasting increase in alpha diversity. There was no major effect of distance to water on taxonomic richness during either season. Beta diversity was as high across as along gradients, and we found support for modular rather than nested community structures along gradients. Our study demonstrated that small‐scale gradients in distance to water can influence several aspects of ant communities in semi‐arid savannas. However, our results also point to strong effects of small‐scale environmental variation, for instance associated with vegetation characteristics, soil properties, and plant community structure that are not directly linked to water access.