Biology subjects

Hillebrand, H.

Publications and source records attributed to Hillebrand, H..

4 recordsLinked to original sources

bioRxiv2026

Space-for-time substitution reveals partial transferability of marine biodiversity-temperature relationships

Forecasts of biodiversity responses to climate change often rely on space-for-time substitution, in which spatial biodiversity-climate relationships are used to predict biodiversity change through time. Yet this approach is rarely tested directly because long-term biodiversity time series are scarce. Here, we combine global modern and fossil assemblage data of planktonic foraminifera with site-specific sea-surface temperature reconstructions to compare biodiversity-temperature relationships across space and time. Spatial and temporal compositional turnover models showed similar slopes but consistently different intercepts, with spatial models predicting higher turnover across the full temperature gradient. Restricting the spatial comparison to the environmental domain of individual fossil time series reduced, but did not eliminate, this intercept mismatch. For alpha diversity, spatial models more closely recovered the temporal biodiversity-temperature relationship than for compositional turnover. Thus, for the timescales studied here, space-for-time substitution captures the direction of biodiversity change but not its magnitude through time.

ecology↗

bioRxiv2026

A growth-maintenance tradeoff determines nutrient-limited growth in phytoplankton

Phytoplankton encounter a range of light and nutrient conditions in nature and must adjust their internal carbon and nitrogen allocations to grow across different resource environments. Current phytoplankton carbon budget models treat respiration simply as a carbon loss. In reality, respiration is a critical cellular process that produces energy for nutrient uptake and cellular maintenance. Drawing on empirical evidence, we developed an eco-physiological model that incorporates a more realistic role of respiration. In our model, photosynthetic carbon is partitioned into: (i) the Pentose Phosphate Pathway (PPP) for assimilation and (ii) respiration for energy production that is then used in nutrient uptake. Stored nitrogen is partitioned between three pools: cellular structure, photosynthesis and nutrient uptake. Using an optimality-based approach, we identify strategies that maximize either exponential growth rate or competitive ability. We find that optimal internal allocations follow a growth-maintenance tradeoff, favoring population growth through carbon acquisition in nitrogen-replete conditions and population maintenance through nitrogen acquisition in nitrogen-limited conditions. The optimal allocations match empirically observed shifts in carbon partitioning at different dilution rates. Our model also generates an interactive growth response surface with an asymmetry, where light is the dominant limiting factor at low light intensities and co-limitation by light and nitrogen only occurs at high light levels. Furthermore, the model recovers the widely accepted Droop function for growth vs nitrogen quota and predicts a hyperbolic decline in growth vs energy quotas. Through a simple growth-maintenance tradeoff, our model provides a mechanistic foundation for predicting phytoplankton productivity in biogeochemical models.

ecology↗

bioRxiv2025

Quantifying the net effect of biodiversity on stability

Understanding the relationship between biodiversity and both the functioning and stability of ecosystems has been a central focus of ecologists for decades. A step-change in our understanding of the biodiversity-ecosystem functioning relationship was enabled by explicit measurement of the additional functioning provided by biodiversity through comparing expected and observed yields in multi-species communities. However, we lack an equivalent measure for stability. Here, we quantify the net biodiversity effect on stability using model simulations and a microcosm experiment that exposed different phytoplankton species and their combinations to temperature increases and fluctuations. As an emergent property of communities, stability frequently exceeded the expected stability of the combined component species, leading to a net biodiversity effect on stability analogous to the effect on functioning. In our simulations, these effects depended on the strength of competitive interactions as well as species composition and their thermal niche. Experimentally, the stabilising effect of diversity was, however, non-linear, greatest for two-species combinations, and varied with both community composition and disturbance regime. Quantifying the net biodiversity effect on stability advances our mechanistic understanding of the biodiversity-stability relationship, and provides crucial information to support ecosystem management and conservation.

ecology↗

bioRxiv2024

Body size is a better predictor of intra- than interspecific variation of animal stoichiometry across realms

Animal stoichiometry affects fundamental processes ranging from organismal physiology to global element cycles. However, it is unknown whether animal stoichiometry follows predictable scaling relationships with body mass and whether adaptation to life on land or water constrains patterns of elemental allocation. To test both interspecific and intraspecific body-size scaling relationships of the nitrogen (N), phosphorus (P), and N:P content of animals, we used a subset of the StoichLife database encompassing 9,933 individual animals (vertebrates and invertebrates) belonging to 1,543 species spanning 10 orders of magnitude of body size from terrestrial, freshwater, and marine realms. Across species, body mass did not explain much variation in %N and %P composition, although the %P of invertebrates decreased with size. The effects of body size on species elemental content were small in comparison to the effects of taxonomy. Body size was a better predictor of intraspecific than interspecific elemental patterns. Between 42 to 45% in intraspecific stoichiometric variation was explained by body size for 27% of vertebrate species and 35% of invertebrate species. Further, differences between organisms inhabiting aquatic and terrestrial realms were observed only in invertebrate interspecific %N, suggesting that the realm does not play an important role in determining elemental allocation of animals. Based on our analysis of the most comprehensive animal stoichiometry database, we conclude that (i) both body size and realm are relatively weak predictors of animal stoichiometry across taxa, and (ii) body size is a good predictor of intraspecific variation in animal elemental content, which is consistent with tissue-scaling relationships that hold broadly across large groups of animals. This research reveals a lack of general scaling patterns in the elemental content across animals and instead points to a large variation in scaling relationships within and among lineages.

ecology↗