Biology subjects

Isbell, F.

Publications and source records attributed to Isbell, F..

9 recordsLinked to original sources

bioRxiv2025

Complementarity of ecosystem types drives landscape-wide productivity in North America

Landscape mosaics with a greater diversity of ecosystems tend to be more productive, mirroring the well-established relationship between species diversity and productivity observed in plot-scale biodiversity experiments. However, the mechanisms driving this effect at the landscape scale remain unclear. Here, we analyze a 15-year time series of satellite-derived primary productivity across over 50,000 landscape plots that vary in ecosystem composition. Our results demonstrate that more diverse landscapes are more productive and more predictable under environmental stress, especially drought. Using statistical partitioning, we show that these diversity effects are primarily driven by complementarity, with productivity gains that are broadly shared among ecosystem types rather than being dominated by a few. The specific ecosystem types that contributed most to landscape functioning varied regionally, but their role in driving mixture productivity remained unaffected by drought. These findings extend biodiversity theory to the landscape scale, emphasizing the critical role of higher-order diversity in shaping ecosystem function and informing landscape management.

ecology↗

bioRxiv2025

Positive effects of landscape diversity on vegetation productivity at the kilometer scale

AO_SCPLOWBSTRACTC_SCPLOWBroad evidence suggests a positive relationship between local species richness and ecosystem functioning 1,2. However, Earths terrestrial surface is formed by a mosaic of different habitats, which constitutes a higher level of diversity known as landscape diversity. Recent studies indicate that landscape diversity can also promote ecosystem functions, including primary productivity, but the underlying mechanisms and relevant spatial scales remain poorly understood 3,4. Here, we combine satellite remote sensing of vegetation productivity with high-resolution land cover data to investigate the effects of landscape diversity on ecosystem functioning across different spatial scales. Using a plot network covering North America, we find that the observed landscape-wide effects cannot be explained by local-scale interactions along ecosystem interfaces. In a subsequent, global-scale analysis, we instead demonstrate that landscape diversity effects are most strongly associated to landscape diversity at a spatial scale of a few kilometers. This association holds across continents and climatic zones, indicating that this pattern is universal. Our investigation therefore suggests that effective land management and biodiversity conservation strategies must integrate both local species richness and higher-level organizational diversity, such as landscape diversity, to ensure robust ecosystem functioning.

ecology↗

bioRxiv2023

Simulating atmospheric drought: Silica gel packets dehumidify mesocosm microclimates

O_LIAs global temperatures rise, droughts are becoming more frequent and severe. To predict how drought might affect plant communities, ecologists have traditionally designed experiments with controlled watering regimes and rainout shelters. Both treatments have proven effective for simulating soil drought. However, neither are designed to directly modify atmospheric drought. C_LIO_LIHere, we detail the efficacy of a silica gel atmospheric drought treatment in outdoor mesocosms with and without a cooccurring soil drought treatment. At California State University, Los Angeles, we monitored relative humidity (RH), temperature, and vapor pressure deficit (VPD) every 10 minutes for five months in a bare-ground experiment featuring mesocosms treated with soil drought (reduced watering) and/or atmospheric drought (silica packets suspended 12 cm above soil). C_LIO_LIWe found that silica packets dehumidified these microclimates most effectively (-5% RH) when combined with reduced soil water, regardless of the ambient humidity levels of the surrounding air. Further, packets increased microclimate VPD most effectively (+0.4 kPa) when combined with reduced soil water and ambient air temperatures above 20{degrees}C. Finally, packets simulated atmospheric drought most consistently when replaced within three days of deployment. C_LIO_LIOur results demonstrate the use of silica packets as effective dehumidification agents in outdoor drought experiments. We emphasize that incorporating atmospheric drought in existing soil drought experiments can improve our understandings of the ecological impacts of drought. C_LI

ecology↗

bioRxiv2022

Nutrient addition increases grassland resistance during dry and wet climate extremes despite functional diversity loss

O_LINutrient enrichment impacts grassland plant diversity such as species richness, functional trait composition and diversity, but whether and how these changes affect ecosystem stability in the face of increasing climate extremes remains largely unknown. C_LIO_LIWe quantified the direct and diversity-mediated effects of nutrient addition (by nitrogen, phosphorus, and potassium) on the stability of aboveground biomass production in 10 long-term grassland experimental sites. We measured five facets of stability as the temporal invariability, resistance during and recovery after extreme dry and wet growing seasons. C_LIO_LILeaf traits (leaf carbon, nitrogen, phosphorus, potassium, and specific leaf area) were measured under ambient and nutrient addition conditions in the field and were used to construct the leaf economic spectrum (LES). We calculated functional trait composition and diversity of LES and of single leaf traits. We quantified the contribution of intraspecific trait shifts and species replacement to change in functional trait composition as responses to nutrient addition and its implications for ecosystem stability. C_LIO_LINutrient addition decreased functional trait diversity and drove grassland communities to the faster end of the LES primarily through intraspecific trait shifts, suggesting that intraspecific trait shifts should be included for accurately predicting ecosystem stability. Moreover, the change in functional trait diversity of the LES in turn influenced different facets of stability. That said, these diversity-mediated effects were overall weak and/or overwhelmed by the direct effects of nutrient addition on stability. As a result, nutrient addition did not strongly impact any of the stability facets. These results were generally consistent using individual leaf traits but the dominant pathways differed. Importantly, major influencing pathways differed using average trait values extracted from global trait databases (e.g. TRY). C_LIO_LISynthesis. Investigating changes in multiple facets of plant diversity and their impacts on multidimensional stability under global changes such as nutrient enrichment can improve our understanding of the processes and mechanisms maintaining ecosystem stability. C_LI

ecology↗

bioRxiv2022

The recovery of biodiversity and species composition after agricultural abandonment across spatial scales

O_LIHuman impacts have led to dramatic biodiversity change which can be highly scale-dependent across space and time. A primary means to manage these changes is via passive (here, the removal of disturbance) or active (management interventions) ecological restoration. The recovery of biodiversity, following the removal of disturbance is often incomplete relative to some kind of reference target. The magnitude of recovery of ecological systems following disturbance depend on the landscape matrix, as well as the temporal and spatial scales at which biodiversity is measured. C_LIO_LIWe measured the recovery of biodiversity and species composition over 27 years in 17 temperate grasslands abandoned after agriculture at different points in time, collectively forming a chronosequence since abandonment from one to eighty years. We compare these abandoned sites with known agricultural land-use histories to never-disturbed sites as relative benchmarks. We specifically measured aspects of diversity at the local plot-scale (-scale, 0.5m2) and site-scale ({gamma}-scale, 10m2), as well as the within-site heterogeneity ({beta}-diversity) and among-site variation in species composition (turnover and nestedness). C_LIO_LIAt our -scale, sites recovering after agricultural abandonment only had 70% of the plant species richness (and [~]30% of the evenness), compared to never-ploughed sites. Within-site {beta}-diversity recovered following agricultural abandonment to around 90% after 80 years. This effect, however, was not enough to lead to recovery at our {gamma}-scale. Richness in recovering sites was [~]65% of that in remnant never-ploughed sites. The presence of species characteristic of the never disturbed sites increased in the recovering sites through time. Forb and legume cover declines in years since abandonment, relative to graminoid cover across sites. C_LIO_LISynthesis. We found that, during the 80 years after agricultural abandonment, old-fields did not recover to the level of biodiversity in remnant never-ploughed sites at any scale. {beta}-diversity recovered more than -scale or {gamma}-scales. Plant species composition recovered, but not completely, over time, and some species groups increased their cover more than others. Patterns of ecological recovery in degraded ecosystems across space and long time-scales can inform effective, targeted active restoration interventions and perhaps, lead to better outcomes. C_LI

ecology↗

bioRxiv2020

Reassembly of soil fungal communities under reforestation and herbivore exclusion

Soil fungi can help improve ecosystem restoration, yet our understanding of how they reassemble in degraded land is limited. Here, we studied fungal community structure using DNA metabarcoding in reforested sites following agricultural abandonment and overgrazing. Two treatments, namely reforestation using different numbers of tree species and deer exclusion, have been applied for multiple decades in the study sites. We found that local fungal richness (alpha diversity) and total fungal richness (gamma diversity) were 1.9-2.9 and 1.3-1.9 times greater, respectively, in reforested stands than in natural forests. These results were regardless of the number of tree species planted in the reforested stands. Conversely, reforested stands had a spatially homogenized community structure with relatively lower degrees of compositional dissimilarity among sites within each stand (beta diversity). These findings were attributable to lower environmental heterogeneity, stronger dispersal limitation, and a comparatively shorter time since the onset of community assembly in reforested stands. Deer exclosures had no detectable effect on fungal community structure. Overall, the agricultural legacy in fungal community structure appears to have persisted for decades, even under proactive restoration of aboveground vegetation. Direct human intervention belowground may therefore be necessary for the recovery of soil biota once altered.

ecology↗

bioRxiv2019

The results of biodiversity-ecosystem functioning experiments are realistic

A large body of research shows that biodiversity loss can reduce ecosystem functioning, thus providing support for the conservation of biological diversity1-4. Much of the evidence for this relationship is drawn from biodiversity-ecosystem functioning experiments (hereafter: biodiversity experiments), in which biodiversity loss is simulated by randomly assembling communities of varying species diversity, and ecosystem functions are measured5-9. This random assembly has led some ecologists to question the relevance of biodiversity experiments to real-world ecosystems, where community assembly may often be non-random and influenced by external drivers, such as climate or land-use intensification10-18. Despite these repeated criticisms, there has been no comprehensive, quantitative assessment of how experimental and real-world plant communities really differ, and whether these differences invalidate the experimental results. Here, we compare data from two of the largest and longest-running grassland biodiversity experiments globally (Jena Experiment, Germany; BioDIV, USA) to related real-world grassland plant communities in terms of their taxonomic, functional, and phylogenetic diversity and functional-trait composition. We found that plant communities of biodiversity experiments have greater variance in these compositional features than their real-world counterparts, covering almost all of the variation of the real-world communities (82-96%) while also containing community types that are not currently observed in the real world. We then re-analysed a subset of experimental data that included only ecologically-realistic communities, i.e. those comparable to real-world communities. For ten out of twelve biodiversity-ecosystem functioning relationships, biodiversity effects did not differ significantly between the full dataset of biodiversity experiments and the ecologically-realistic subset of experimental communities. This demonstrates that the results of biodiversity experiments are largely insensitive to the inclusion/exclusion of unrealistic communities. By bridging the gap between experimental and real-world studies, these results demonstrate the validity of inferences from biodiversity experiments, a key step in translating their results into specific recommendations for real-world biodiversity management.

ecology↗

bioRxiv2018

Biodiversity trends are stronger in marine than terrestrial assemblages

Human activities have fundamentally altered biodiversity. Extinction rates are elevated and model projections suggest drastic biodiversity declines. Yet, observed temporal trends in recent decades are highly variable, despite consistent change in species composition. Here, we uncover clear spatial patterns within this variation. We estimated trends in the richness and composition of assemblages in over 50,000 time-series, to provide the most comprehensive assessment of temporal change in biodiversity across the planet to date. The strongest, most consistent pattern shows compositional change dominated by species turnover, with marine taxa experiencing up to fourfold the variation in rates of change of terrestrial taxa. Richness change ranged from no change to richness gains or losses of ~10% per year, with tropical marine biomes experiencing the most extreme changes. Earth is undergoing a process of spatial reorganisation of species and, while few areas are unaffected, biodiversity change is consistently strongest in the oceans.

ecology↗

bioRxiv2018

The geography of the Anthropocene differs between the land and the sea

O_LIClimate change and other anthropogenic drivers of biodiversity change are unequally distributed across the world. The geographic patterns of different drivers, and the spatial overlap among these drivers, have important implications for the direction and pace of biodiversity change, yet are not well documented. Moreover, it is unknown if the geographic patterns of drivers differ between the terrestrial and marine realm, as expected due to marked differences in how humans interact with the land and ocean. C_LIO_LIWe compiled global gridded datasets on climate change, land-use, resource exploitation, pollution, species invasions, and human population density. We used multivariate statistics to examine the spatial relationships among the datasets and to characterize the typical combinations of drivers experienced by different parts of the world. C_LIO_LIWe found stronger positive correlations among drivers in the terrestrial than in the marine realm, leading to areas of high intensities of multiple drivers on land. Climate change tended to be negatively correlated with other drivers in the terrestrial realm (e.g., in the tundra and boreal forest with high climate change but low human use and pollution) whereas the opposite was true in the marine realm (e.g., in the Indo-Pacific with high climate change and high fishing). C_LIO_LIWe show that different regions of the world can be defined by anthropogenic threat complexes (ATCs), distinguished by different sets of drivers with varying intensities. The ATCs can be used to test hypothesis about the pattern of biodiversity change, especially the joint effects of multiple drivers. More generally, our global analysis highlights the broad conservation priorities needed to mitigate the effects of anthropogenic change on biodiversity responses, with different priorities emerging on land and in the ocean, and in different parts of the world. C_LI

ecology↗