Biology subjects

Alroy, J.

Publications and source records attributed to Alroy, J..

3 recordsLinked to original sources

bioRxiv2023

Tree species richness and evenness affect forest biomass differently across biogeographic regions

The relationship between tree species diversity, measures of forest structure, and forest biomass has long been debated, with local- or continental-scale studies often finding contrasting results. Given the importance of forests as global carbon sinks, understanding the characteristics that underpin biomass accumulation is thus a critical component of mitigating climate change. Here we present a global analysis of 11,400 forest plots, sourced from scientific publications and forest inventories, to investigate the association of forest basal area (used as a proxy for biomass) with stem density and measures of tree species diversity (richness and evenness). We used generalised additive models to account for the confounding effects of climate and spatial signal and we modelled the density, climate, and diversity effects both globally and for each biogeographic region. Stem density showed a strong positive association with basal area across all biogeographic regions, while the effect of species richness varied. In the Palearctic, Nearctic, and Neotropical biogeographic regions, basal area was positively associated with species richness, although this was only detectable for lower values of basal area. In the Ethiopian and Oriental biogeographic regions there was no relationship between richness and basal area, while in the Australian biogeographic regions it was negative. The weak-to-no association between species evenness and basal area in all bioregions other than Australia suggests that the overall correlation emerges from processes operating at more local scales. Our results highlight the importance of accounting for biogeographic processes when evaluating strategies to mitigate climate change and support nature conservation.

ecology↗

bioRxiv2021

Global distribution of mammal herbivore biomass reveals megafauna extinction patterns

Mammalian herbivores strongly shape Earth system processes. A lack of global dynamic models of mammal populations limits our understanding of their ecological role at large scales and the consequences of their extinctions. We developed a mechanistic global model of terrestrial herbivore populations simulated with 37 functional groups defined by analyzing eco-physiological traits of all extant herbivores (n = 2599). We coupled this model with a global vegetation model to predict herbivores biomass maximum potential (pre-industrial) and at present. Natural ecosystems could have sustained a wild herbivore wet biomass of 330 Mt, comprised of 192 Mt by large (body mass > 5 kg) and 138 Mt by small species. Anthropogenic activity reduced large herbivores biomass by 57%, estimated now at 82 Mt; consequently, small herbivores now dominate global herbivore biomass with 98 Mt (-29%). Losses vary greatly across climatic zones and functional groups, suggesting that size is not the only discriminant feature of biomass decline. Actual evapotranspiration is the most important driver of total, large, and small herbivore biomass and explains 64%, 59%, and 49% of its variation, respectively. Energy and water dependency is high for large herbivores, whose biomass is greater in hot and wet areas, challenging the notion that large herbivore biomass peaks in savannas only. Outside Africa and the Tropics, potential-biomass hotspots occur in areas today dominated by humans; this could undermine the recovery of larger species in certain areas. These herbivore biomass estimates provide a quantitative benchmark for setting conservation and rewilding goals at large spatial scales. The herbivore model and functional classification create new opportunities to integrate mammals into Earth System science and models.

ecology↗

bioRxiv2018

The R package divDyn for quantifying diversity dynamics using fossil sampling data

O_LIUnbiased time series of diversity dynamics are vital for quantifying the grand history of life. Applications include identifying ancient mass extinctions and inferring both biotic and abiotic controls on diversification rates.\nC_LIO_LIWe introduce divDyn, a new R package that facilitates the calculation of taxonomic richness, extinction and origination rates from time-binned fossil sampling data. State-of-the-art sampling completeness metrics, counting protocols, and sampling standardisation functions permit the reconstruction of biologically meaningful time series. Additional functions permit the partitioning of turnover rates by trait and environmental affinity.\nC_LIO_LIWe display Phanerozoic-scale diversity dynamics of marine invertebrates using the divDyn package. Using the core function and standard subsampling options, we revisit earlier assessments of declining extinction and origination rates over time and of equilibrial diversity dynamics to assess their methodological dependency.\nC_LIO_LIThe modular and fast implementation of published methods ensures traceability, reproducibility, and comparability of future studies.\nC_LI

paleontology↗