Biology subjects

Strubbe, D.

Publications and source records attributed to Strubbe, D..

11 recordsLinked to original sources

bioRxiv2026

Beyond establishment: incorporating physiological performance into predictions of invasion risk

Biological invasions are a major driver of global change, reshaping ecosystems and threatening biodiversity worldwide. Anticipating where invaders will establish and where they will exert the strongest ecological impacts are key challenges for early detection and targeted management. Although Species Distribution Models (SDMs) are widely used to forecast biological invasions, they often provide uncertain estimates of establishment ranges and limited insight into invader performance, making it difficult to anticipate ecological impacts. Here, we address these limitations by integrating physiological information on invader performance with SDMs to identify regions of high invasion risk. Using the brown alga Rugulopteryx okamurae, one of the most prominent marine invaders in Europe, we first test alternative hypotheses of northern establishment limits: (i) a cold-survival constraint driven by winter temperatures and (ii) a growth constraint derived from the species' thermal performance. To identify the more likely scenario, we combine cold-tolerance experiments with seasonal growth comparisons between the invader and a native macroalga Dictyota dichotoma, whose established distribution allows physiological performance to be directly related to realised presence. Finally, we project seasonal growth of the invader across the predicted establishment range as a proxy for biomass accumulation and potential ecological impacts. Our results indicate that northern limit in Europe will be more likely constrained by winter survival rather than growth, extending the potential establishment range of Rugulopteryx to mid-Norway. In contrast, the highest impacts are likely to remain concentrated in southern Europe, where thermal conditions sustain high year-round growth. Overall, our approach illustrates how understanding the physiological response of invaders to their environment can improve the interpretation of SDM outputs and help identify areas at greatest risk of impact within their potential establishment range.

ecology↗

bioRxiv2025

Predicting current and future distribution of the common waxbill using a mechanistic modelling approach

Biological invasions and climate change are two of the most pressing drivers of biodiversity loss worldwide. Anticipating where invasive species are likely to establish, as well as the potential impact of climate change on their range expansion, is essential for early detection and targeted management. In this study, we use a mechanistic species distribution model (SDM) to evaluate the current and future areas at risk of invasion by the common waxbill (Estrilda astrild), a widespread avian invader. Our model accurately predicts the species current range in Iberia and identifies additional climatically suitable areas, particularly in southern and western Europe. Under warming scenarios of +2 {degrees}C and +4 {degrees}C, suitable areas expand northwards, with over two-thirds of Europe classified as suitable under the most extreme scenario. These results suggest that the species is already operating near the cold limits of its thermal niche in parts of its invasive range, and that rising temperatures may remove these constraints, allowing expansion into previously unsuitable areas. Our findings demonstrate the power of mechanistic models in identifying regions at risk of colonisation and underscore the importance of early intervention and targeted monitoring in areas projected to become suitable.

ecology↗

bioRxiv2025

Weak evaporative cooling capacity and body size shape thermal limits in tropical montane forest birds

Climate warming and forest fragmentation threaten tropical biodiversity by altering microclimates and narrowing the range of temperatures within which species can maintain optimal physiological performance. We investigated the thermoregulatory capacities of five forest-dependent bird species from the Taita Hills (Kenya), a montane biodiversity hotspot experiencing severe habitat loss. Using respirometry, we measured resting metabolic rate (RMR) across a range of temperatures to determine thermoneutral zone (TNZ) limits, quantified evaporative water loss (EWL), evaporative heat loss (EHL), and metabolic heat production (MHP) as proxies of cooling capacity, and estimated heat tolerance limits (HTLs). Contrary to expectations of a classical TNZ pattern, RMR-temperature relationships were predominantly V-shaped, suggesting the absence, or marked narrowness, of a TNZ. In contrast, HTL clearly increased with body mass, with larger species tolerating higher temperatures. Evaporative cooling efficiency remained weak across all species (EHL/MHP < 1), indicating limited capacity to dissipate metabolic heat. Compared with global data, the Taita Hills species exhibited low critical temperatures and narrow thermal ranges, consistent with specialisation to the stable microclimates of tropical montane forests. Our findings suggest that small-bodied, forest-dependent tropical birds function within narrow thermal margins, which may make them especially vulnerable to rising temperatures and the microclimatic changes associated with climate change and forest fragmentation.

ecology↗

bioRxiv2025

Metabolic responses at sub-thermoneutral temperatures in captive common waxbills (Estrilda astrild)

Understanding how endotherms manage energy expenditure at sub-thermoneutral temperatures is crucial for predicting their physiological flexibility and adaptive potential. This study investigated the metabolic responses of captive-bred common waxbills (Estrilda astrild) to decreasing ambient temperatures, with a focus on three questions: whether basal metabolic rate (BMR) predicts standard metabolic rate (SMR), how consistent individual metabolic responses are, and whether waxbills employ cold-induced energy-saving mechanisms. We found that BMR did not reliably predict SMR, underscoring the limits of BMR as a proxy under ecologically relevant conditions. SMR showed moderate repeatability across individuals, but variation was mainly due to baseline metabolic level rather than slope differences in thermal reaction norms. A two-breakpoint model best described the relationship between temperature and metabolic rate, with a marked decline in SMR below ~18.8{degrees}C. This decrease, along with observed reductions in core body temperature in some individuals, reveals an energy-saving strategy involving shallow hypothermia at relatively mild sub-thermoneutral temperatures. These findings suggest that energy-saving mechanisms may be intrinsic to the species rather than purely plastic responses. Overall, our results highlight both the limitations of BMR and the importance of measuring metabolic responses across thermal gradients to detect subtle but ecologically relevant hypometabolic strategies.

ecology↗

bioRxiv2025

Multitaxon assessment reveals inconsistent biodiversity responses to forest structural complexity in temperate forests

Increasing forest structural complexity is a key objective of future-proof forest management, with potential benefits for biodiversity. However, empirical evidence for consistent biodiversity-structure relationships across taxa is still limited. We investigated whether structurally more complex forests support greater species richness and higher multidiversity across taxonomic and functional groups in 19 mature forest plots in Flanders, Belgium. As one of the most densely populated and urbanized regions in Europe, with limited and highly fragmented forest cover, Flanders provides a particularly informative and policy-relevant context to test structure-biodiversity relationships. Its forests, often dominated by a few tree species and subject to long-term anthropogenic pressures and management, represent a realistic gradient of structural complexity. Structural complexity was quantified using a Structural Complexity Index (SCI), and biodiversity was assessed using a multidiversity index integrating scaled species richness across five taxonomic and seven arthropod functional groups. Using mixed-effects models and multivariate Bayesian analyses, we tested both direct effects of SCI on biodiversity and the covariation in species richness among groups. Contrary to expectations, SCI was not a consistent predictor of multidiversity, and most groups showed weak or inconsistent responses. These findings might suggest that structural complexity alone may be insufficient to enhance biodiversity in simplified forests. HighlightsO_LIForest structural complexity does not consistently predict biodiversity. C_LIO_LIResponses vary among taxonomic and functional groups. C_LIO_LICross-taxon congruence in diversity is limited and scale-dependent. C_LIO_LIKeywords: Forest structural complexity; Multidiversity, Species richness; Functional groups; Sustainable forest management C_LI

ecology↗

bioRxiv2024

Ixodes ricinus nymphs prefer blood with Borrelia infection and low corticosteroid concentration

Ticks play a significant role in the transmission of various pathogens, impacting both human and animal health. Understanding the factors influencing tick feeding preferences is crucial for mitigating the risk of tick-borne diseases. This study investigates the blood preference of Ixodes ricinus nymphs, focusing on host species, stress hormone levels (glucocorticoids), and the presence of Borrelia burgdorferi bacteria. Three series of in vitro experiments were conducted. The setup involved placing individual blood drops (15 {micro}l) on filter paper over a 37{degrees}C plate. Ticks were placed in the center, and their movements were tracked for two minutes to record preferences. The first experiment evaluated the ticks preference for blood from different hosts (mouse, bird, sheep). The second experiment explored the role of stress hormones by assessing the ticks response to blood with varying levels of supplemented cortisol and corticosterone (0, 10, 100 and 1000 ng/ml). The third experiment examined the potential influence of Borrelia infection, combined with elevated stress hormone levels, on blood preference. Our results show that I. ricinus nymphs show a significant preference for blood without added glucocorticoids and, in mice, blood with Borrelia infection. No clear preference for a specific host species was observed. These findings provide valuable insights into the complex interactions between ticks, blood characteristics, and Borrelia infection status, highlighting the potential importance of host physiological state in tick host selection. Future studies should explore the mechanisms behind these preferences, which could lead to the development of new methods to control the spread of tick-borne diseases. HIGHLIGHTSO_LIIn vitro experiments with nymphs can reveal insights into their blood preferences C_LIO_LITicks displayed no difference in preference towards bird, mouse, or sheep blood C_LIO_LITicks prefer blood with baseline stress levels over increased stress levels C_LIO_LIMouse blood infected with Borrelia burgdorferi was preferred by ticks C_LI

ecology↗

bioRxiv2024

Metabolic responses to cold: thermal physiology of native common waxbills (Estrilda astrild)

Ecophysiological studies of invasive species tend to focus on captive individuals and their invasive range. However, the importance of gaining a thorough understanding of their physiology in their native range, where autecological knowledge is limited, has played a crucial role in assessing species ecophysiological responses to the often novel environmental conditions encountered in their invasive range. Here, we investigated the ecophysiological characteristics of a population of the wild-caught common waxbill (Estrilda astrild), a successful global invader, in part of its native range (South Africa). We investigated how this species adjusts its resting metabolic rate over a range of temperatures to identify its thermoneutral zone (TNZ) as an indicator of a species thermal tolerance. The observed TNZ curve predominantly followed the classic Scholander-Irving model, with metabolic rates increasing linearly at temperatures outside the TNZ. However, we found an inflection point at moderately cold temperatures (16{degrees}C) where the common waxbill began to decrease its metabolic rate. This finding highlights the potential use of an energy-saving strategy as an adaptive response to cold, such as facultative hypothermic responses through a reduction in body temperature, which may explain their success as an invasive species. We argue that although metabolic infection points have been repeatedly identified in studies of TNZ, the specific mechanisms behind metabolic down-regulation at low temperatures remain underexplored in the literature. We therefore suggest that future research should focus on investigating body temperature variation, with particular emphasis on its potential contribution to metabolic adaptation in colder environments.

ecology↗

bioRxiv2023

Metabolic adjustments to winter severity in two geographically separated great tit (Parus major) populations

Understanding the potential limits placed on organisms by their ecophysiology is crucial for predicting their responses to varying environmental conditions. Studies to date have traditionally relied on between-species comparisons, however, recently, there has been a growing recognition of the importance of intraspecific variation in shaping an organisms ecological and physiological responses. In this context, widely distributed resident bird species offer a well-suited study system to examine intraspecific geographical variation in ecophysiological traits. A main hypothesis for explaining avian thermoregulatory mechanisms is the aerobic capacity model, which posits a positive correlation between basal (BMR) and summit (Msum) metabolism, caused by the energetic maintenance costs associated with increased muscle mass for shivering thermogenesis and enhanced investment in digestive organs for food processing. Most evidence for this hypothesis, however, comes from interspecific comparisons only, and the ecophysiological underpinnings of avian thermoregulatory capacities hence remain controversial. Here, we focus on great tits (Parus major), measuring winter BMR and Msum in two populations from different climates, a maritime-temperate (Gontrode, Belgium) and a continental (Zvenigorod, Russia) one. We test for the presence of intraspecific geographical variation in metabolic rates and assess the predictions following the aerobic capacity model. We found that metabolic rates differed between populations, whereby the birds from the maritime-temperate climate (Gontrode) showed higher (whole-body and mass-independent) BMR whereas conversely, great tits from Zvenigorod showed higher levels of both (whole-body and mass-independent) Msum. Within each population, our data did not fully support the aerobic capacity models predictions. We argue that the decoupling of BMR and Msum observed may be caused by different selective forces acting on these metabolic rates, with birds from the continental-climate Zvenigorod population facing the need to conserve energy for surviving long winter nights (by keeping their BMR at low levels) while simultaneously being able to generate more heat (i.e., a high Msum) to withstand cold spells. We argue that the coupling or uncoupling of basal and maximum metabolic rates at the intraspecific level is likely influenced by different selective pressures that shape local adaptations in response to different climate regimes.

ecology↗

bioRxiv2023

Seasonal variation in great tit (Parus major) energy requirements: reallocation versus increased demand

Understanding how birds annually allocate energy to cope with changing environmental conditions and physiological states is a fundamental question in avian ecology. The two main hypotheses to explain annual patterns in energy use are "reallocation" and "increased demand". The reallocation hypothesis suggests equal energetic costs in winter and breeding seasons, while the increased demand suggests that energy demand should be highest during breeding. Under the standard aerobic capacity model of endothermy, birds are expected to adjust the mass and/or metabolic intensity of their bodies in ways that are consistent with expected cold- and/or activity-induced costs. Here, we look for metabolic signatures of reallocation versus increased demands in the energy requirements of a small, resident passerine of a temperate-zone (great tit, Parus major). To do so, we measured whole-body and mass-independent basal (BMR), summit (Msum), and field (FMR) metabolic rates during late winter and during the chick-rearing period (breeding). We also assessed whether, and to what extent, metabolic rates conform to the predictions of the aerobic capacity model of endothermy. We found that great tits showed no substantial differences in energy expenditure between winter and the breeding season, providing support for the reallocation hypothesis. Only mass-independent Msum showed seasonal variation, with significantly higher values ([~]4%) in winter compared to the breeding season. Our results also lend support to the predictions of the aerobic capacity model for the evolution of endothermy, as we found that whole-body BMR and Msum were positively related. We argue that both energy reallocation and the limited increase in mass-independent Msum are consistent with the relatively mild winter temperatures recorded during our study period. Our results confirm that both BMR and Msum are flexible traits that vary in ways that are consistent with expected cold- and/or activity-induced costs.

ecology↗

bioRxiv2020

Host-pathogen co-existence incurs reproductive costs

Widespread endemism of host-adapted pathogens poses a heavy burden on animal and human health. Mechanisms underpinning long-term host pathogen co-existence and concurrent costs are poorly understood. We use infections in pigeons with pathogenic, pigeon adapted Salmonella Typhimurium to explain how host and pathogen trade-offs and benefits sustain long-term pathogen endemism. An experimentally infected group of pigeons that was studied for 15 months showed that pathogen persistence decreased host condition and reproductive success, but conferred protection against Salmonella-induced clinical disease. The relevance of these findings was confirmed in nature, where this pathogen was shown to widely occur in feral pigeons (Columba livia), yet without clinical disease. Pathogen transmission and long-term persistence were associated with intermittent faecal shedding, which markedly increased during crop feeding and natural stress periods. Exploiting host specific traits in the presence of protective host population immunity thus facilitates long-term co-existence, be it at a significant reproductive cost.

microbiology↗

bioRxiv2020

Occurrence cubes: a new paradigm for aggregating species occurrence data

In this paper we describe a method of aggregating species occurrence data into what we coined "occurrence cubes". The aggregated data can be perceived as a cube with three dimensions - taxonomic, temporal and geographic - and takes into account the spatial uncertainty of each occurrence. The aggregation level of each of the three dimensions can be adapted to the scope. Built on Open Science principles, the method is easily automated and reproducible, and can be used for species trend indicators, maps and distribution models. We are using the method to aggregate species occurrence data for Europe per taxon, year and 1km2 European reference grid, to feed indicators and risk mapping/modelling for the Tracking Invasive Alien Species (TrIAS) project.

ecology↗