Climate warming is the defining environmental crisis of the 21st century. Elucidating whether organisms can adapt to rapidly changing thermal environments is therefore a crucial research priority.

Abstract

Climate warming is the defining environmental crisis of the 21st century. Elucidating whether organisms can adapt to rapidly changing thermal environments is therefore a crucial research priority. We investigated warming effects on a native Hemipteran insect (Murgantia histrionica) that feeds on an endemic plant species (Isomeris arborea) of the California coastal sage scrub. Experiments conducted in 2009 quantified the temperature responses of juvenile maturation rates and stage-specific and cumulative survivorship. The intervening decade has seen some of the hottest years ever recorded, with increasing mean temperatures accompanied by an increase in the frequency of hot extremes. Experiments repeated in 2021 show a striking change in the bugs' temperature responses. In 2009, no eggs developed past the second nymphal stage at 33°C. In 2021, eggs developed into reproductive adults at 33°C. Upper thermal limits for maturation and survivorship have increased, along with a decrease in mortality risk with increasing age and temperature, and a decrease in the temperature sensitivity of mortality with increasing age. While we cannot exclude the possibility that other environmental factors occurring in concert could have affected our findings, the fact that all observed trait changes are in the direction of greater heat tolerance suggests that consistent exposure to extreme heat stress may at least be partially responsible for these changes. Harlequin bugs belong to the suborder Heteroptera, which contains a number of economically important pests, biological control agents and disease carriers. Their differential success in withstanding warming compared to beneficial holometabolous insects such as pollinators may exacerbate the decline of beneficial insects due to other causes (e.g. pollution and pesticides) with potentially serious consequences on both biodiversity and ecosystem functioning.

We document a greater movement diversity for both the Norwegian coastal cod and the Northeast Arctic cod than previously detected by population level-monitoring. This observed movement diversity promotes sympatric fjord residency, information which is of great relevance for the management of these ecotypes.

Abstract

Movement diversity within species represent an important but often neglected, component of biodiversity that affects ecological and genetic interactions, as well as the productivity of exploited systems. By combining individual tracking data from acoustic telemetry with novel genetic analyses, we describe the movement diversity of two Atlantic cod Gadus morhua ecotypes in two high-latitude fjord systems: the highly migratory Northeast Arctic cod (NEA cod) that supports the largest cod fishery in the world, and the more sedentary Norwegian coastal cod, which is currently in a depleted state. As predicted, coastal cod displayed a higher level of fjord residency than NEA cod. Of the cod tagged during the spawning season, NEA cod left the fjords permanently to a greater extent and earlier compared to coastal cod, which to a greater extent remained resident and left the fjords temporarily. Despite this overall pattern, horizontal movements atypical for the ecotypes were common with some NEA cod remaining within the fjords year-round and some coastal cod displaying a low fjord fidelity. Fjord residency and exit timing also differed with spawning status and body size, with spawning cod and large individuals tagged during the feeding season more prone to leave the fjords and earlier than non-spawning and smaller individuals. While our results confirm a lower fjord dependency for NEA cod, they highlight a movement diversity within each ecotype and sympatric residency between ecotypes, previously undetected by population-level monitoring. This new knowledge is relevant for the management, which should base their fisheries advice for these interacting ecotypes on their habitat use and seasonal movements.

Positive biotic interactions expand organisms' niche breadths, and promote species coexistence, but few studies have measured how beneficiary traits relate to facilitation strength across environmental gradients. The authors demonstrate that functional traits of animal beneficiaries and environmental context simultaneously govern the strength of biotic interactions in stream ecosystems.

Abstract

Ecosystem engineers modify habitats in ways that facilitate other community members by ameliorating harsh conditions. The strength of such facilitation is predicted to be influenced by both beneficiary traits and abiotic context. One key trait of animals that could control the strength of facilitation is beneficiary body size because it should determine how beneficiaries fit within and exploit stress ameliorating habitat modifications. However, few studies have measured how beneficiary body size relates to facilitation strength along environmental gradients. We examined how the strength of facilitation by net-spinning caddisflies on invertebrate communities in streams varied along an elevation gradient and based on traits of the invertebrate beneficiaries. We measured whether use of silk retreats as habitat concentrated invertebrate density and biomass compared to surrounding rock surface habitat and whether the use of retreat habitat varied across body sizes of community members along the gradient. We found that retreats substantially concentrated the densities of a diversity of taxa including eight different Orders, and this effect was greatest at high elevations. Caddisfly retreats also concentrated invertebrate biomass more as elevation increased. Body size of invertebrates inhabiting retreats was lower than that of surrounding rock habitats at low elevation sites, however, body size between retreats and rocks converged at higher elevation sites. Additionally, the body size of invertebrates found in retreats varied within and across taxa. Specifically, caddisfly retreats functioned as a potential nursery for taxa with large maximal body sizes. However, the patterns of this taxon-specific nursery effect were not influenced by elevation unlike the patterns observed based on community-level body size. Collectively, our results indicate that invertebrates use retreats in earlier life stages or when they are smaller in body size independent of life stage. Furthermore, our analysis suggests that facilitation strength intensifies as elevation increases within stream invertebrate communities. Further consideration of how trait variation and environmental gradients interact to determine the strength and direction of biotic interactions will be important as species ranges and environmental conditions continue to shift.

The authors use a long-term experiment spanning more than two decades to show that a large herbivore (moose) has significant impacts on boreal plant communities but little effect on boreal soils. The data show that soils may be resilient to above-ground impacts in unproductive ecosystems such as the boreal forest.

Abstract

1.

Experimental studies across biomes demonstrate that herbivores can have significant effects on ecosystem functioning. Herbivore effects, however, can be highly variable with studies demonstrating positive, neutral or negative relationships between herbivore presence and different components of ecosystems. Mixed effects are especially likely in the soil, where herbivore effects are largely indirect mediated through effects on plants.

We conducted a long-term experiment to disentangle the effects of non-native moose in boreal forests on plant communities, nutrient cycling, soil composition and soil organism communities.

To explore the effect of moose on soils, we conduct separate analyses on the soil organic and mineral horizons. Our data come from 11 paired exclosure-control plots in eastern and central Newfoundland, Canada that provide insight into 22–25 years of moose herbivory. We fit piecewise structural equations models (SEM) to data for the organic and mineral soil horizons to test different pathways linking moose to above-ground and below-ground functioning.

The SEMs revealed that moose exclusion had direct positive impacts on adult tree count and an indirect negative impact on shrub percent cover mediated by adult tree count. We detected no significant impact of moose on soil microbial C:N ratio or net nitrogen mineralization in the organic or mineral soil horizon. Soil temperature and moisture, however, was more than twice as variable in the presence (i.e. control) than absence (i.e. exclosure) of moose. Overall, we observed clear impacts of moose on above-ground forest components with limited indirect effects below-ground. Even after 22–25 years of exclusion, we did not find any evidence of moose impacts on soil microbial C:N ratio and net nitrogen mineralization.

Our long-term study and mechanistic path analysis demonstrates that soils can be resilient to ungulate herbivore effects despite evidence of strong effects above-ground. Long-term studies and analyses such as this one are relatively rare yet critical for reconciling some of the context-dependency observed across studies of ungulates effects on ecosystem functions. Such studies may be particularly valuable in ecosystems with short growing seasons such as the boreal forest.

The study examined the relationship between climate, physiology and distribution of Lampropholis skinks in eastern Australia. Widespread species showed broader physiological tolerance than range-restricted species, and incorporating physiological and behavioural data improved species distribution models, particularly for range-restricted species.

Abstract

Climate has a key impact on animal physiology, which in turn can have a profound influence on geographic distributions. Yet, the mechanisms linking climate, physiology and distribution are not fully resolved. Using an integrative framework, we tested the predictions of the climatic variability hypothesis (CVH), which states that species with broader distributions have broader physiological tolerance than range-restricted species, in a group of Lampropholis skinks (8 species, 196 individuals) along a latitudinal gradient in eastern Australia. We investigated several physiological aspects including metabolism, water balance, thermal physiology, thermoregulatory behaviour and ecological performance. Additionally, to test whether organismal information (e.g. behaviour and physiology) can enhance distribution models, hence providing evidence that physiology and climate interact to shape range sizes, we tested whether species distribution models incorporating physiology better predict the range sizes than models using solely climatic layers. In agreement with the CVH, our results confirm that widespread species can tolerate and perform better at broader temperature ranges than range-restricted species. We also found differences in field body temperatures, but not thermal preference, between widespread and range-restricted species. However, metabolism and water balance did not correlate with range size. Biophysical modelling revealed that the incorporation of physiological and behavioural data improves predictions of Lampropholis distributions compared with models based solely on macroclimatic inputs, but mainly for range-restricted species. By integrating several aspects of the physiology and niche modelling of a group of ectothermic animals, our study provides evidence that physiology correlates with species distributions. Physiological responses to climate are central in establishing geographic ranges of skinks, and the incorporation of processes occurring at local scales (e.g. behaviour) can improve species distribution models.

The increasing availability of fine-scale animal movement data facilitates various options to investigate behaviour-specific habitat selection. Using hidden Markov models and step-selection functions on muskox GPS-tracking data, this study compares different approaches to account for behaviour, highlights methodological intricacies and demonstrates that especially the definition of the availability domain impacts inference. © Lars Holst Hansen.

Abstract

Animal habitat selection—central in both theoretical and applied ecology—may depend on behavioural motivations such as foraging, predator avoidance, and thermoregulation. Step-selection functions (SSFs) enable assessment of fine-scale habitat selection as a function of an animal's movement capacities and spatiotemporal variation in extrinsic conditions. If animal location data can be associated with behaviour, SSFs are an intuitive approach to quantify behaviour-specific habitat selection. Fitting SSFs separately for distinct behavioural states helped to uncover state-specific selection patterns. However, while the definition of the availability domain has been highlighted as the most critical aspect of SSFs, the influence of accounting for behaviour in the use-availability design has not been quantified yet. Using a predator-free population of high-arctic muskoxen Ovibos moschatus as a case study, we aimed to evaluate how (1) defining behaviour-specific availability domains, and/or (2) fitting separate behaviour-specific models impacts (a) model structure, (b) estimated selection coefficients and (c) model predictive performance as opposed to behaviour-unspecific approaches. To do so, we first applied hidden Markov models to infer different behavioural modes (resting, foraging, relocating) from hourly GPS positions (19 individuals, 153–1062 observation days/animal). Using SSFs, we then compared behaviour-specific versus behaviour-unspecific habitat selection in relation to terrain features, vegetation and snow conditions. Our results show that incorporating behaviour into the definition of the availability domain primarily impacts model structure (i.e. variable selection), whereas fitting separate behaviour-specific models mainly influences selection strength. Behaviour-specific availability domains improved predictive performance for foraging and relocating models (i.e. behaviours with medium to large spatial displacement), but decreased performance for resting models. Thus, even for a predator-free population subject to only negligible interspecific competition and human disturbance we found that accounting for behaviour in SSFs impacted model structure, selection coefficients and predictive performance. Our results indicate that for robust inference, both a behaviour-specific availability domain and behaviour-specific model fitting should be explored, especially for populations where strong spatiotemporal selection trade-offs are expected. This is particularly critical if wildlife habitat preferences are estimated to inform management and conservation initiatives.

In this study the authors thoroughly investigate state-dependent optimal decisions in high-latitude bat populations through a detailed model framework, and test the model application by comparing its predictions to data collected on northern bats.

Abstract

Strong seasonality at high latitudes represents a major challenge for many endotherms as they must balance survival and reproduction in an environment that varies widely in food availability and temperature. To avoid energetic mismatches caused by limited foraging time and stochastic weather conditions, bats employ the energy-saving state of torpor during summer to save accumulated energy reserves. However, at high-latitude small-bats-in-summer face a particular challenge: as nocturnal foragers, they rely on the darkness at night to avoid predators and/or interspecific competition, but live in an environment with short, light summer nights, and even a lack of true night at the northernmost distributions of some bat species. To predict optimal behaviour in relation to latitudinal variation in diurnal cycles, we constructed a stochastic dynamic programming model of bats living at high latitudes. Using a stochastic dynamic programming framework with values that are representative for our study system, we show that individual energetic reserves are a strong driver of daytime use of torpor and night-time foraging behaviour alike, with these linked effects being both temperature- and photoperiod-dependent. We further used the model to predict survival probabilities at five locations across a latitudinal gradient (60.1° N to 70.9° N), finding that combinations of photoperiod and temperature conditions limited population distributions in the model. To verify our model results, we compared predictions for optimal decisions with our own empirical data collected on northern bats (Eptesicus nilssonii) from two latitudes in Norway. The similarities between our predictions and observations provide strong evidence that this model framework incorporates the most important drivers of diurnal decision-making in bat physiology and behaviour. Comparing empirical data and model predictions also revealed that bats facing lighter night conditions further north restrict their mass gain, which strengthens the hypothesis that predation threat is a main driver of bat nocturnality. Our model findings regarding state-dependent decisions in bats should contribute to the understanding of how bats cope with the summer challenges at high latitudes.

Previous work on fire effects on parasites have focused on the direct impact of fire on parasite survival. Here, we show that concentrated herbivory following fire can lengthen the effects of fire on free-living parasites, and create divided landscapes with burned and unburned areas that have distinct infection risks.

Abstract

Fires in grassy ecosystems consume vegetation and initiate high-quality regrowth, which results in pyric herbivory when mammalian grazers concentrate feeding in recent burns. For environmentally transmitted parasites with transmission mechanisms linked to vegetation structure, fire should exert direct effects on parasites, as well as indirect effects resulting from subsequent enhanced herbivory, which can affect parasite input and exposure to environmental conditions. We combined an experimental manipulation with observational data in the Serengeti National Park to investigate the direct and indirect effects of fire on parasites. We assessed the direct effects of fire by measuring changes in parasitic nematode larvae in the grass layer before and after fire on paired experimental burned and control plots. To investigate indirect effects linked to pyric herbivory, we sampled herbivore dung, grass biomass, ground temperature and larval densities every month for 5 months following fire in seven pairs of burned and unburned monitoring plots. Finally, to assess if fire-driven changes to larval densities affected host infection burdens, we collected faecal samples from a key host, Grant's gazelle (Nanger granti), each month for 5 months to estimate within-host parasite burdens. Fire killed all larvae and increased grazer dung inputs by 40% for 2 months following fire. Dung inputs after fire led to larval parasite recolonization of burned patches, but intense herbivory kept grass short and larval densities were associated with changes in ground temperature linked to grass biomass and ambient temperature. Grant's gazelles had lower parasite burdens when sampled in areas with higher compared to lower burned area fraction. Fire and pyric herbivory change the densities of larval parasites in the environment and divide the landscape into burned and unburned regions with distinct infection risks for local herbivores. The indirect effects quantified here represent a novel finding with major implications for all grazing systems impacted by fire.

Muhtasari

Mioto katika mifumo ikolojia yenye nyasi nyingi humaliza mimea na kuanzisha uotaji upya wa malisho yenye virutubisho jambo ambalo husababisha ulaji mwingi wa nyasi baada ya moto wakati mamalia walao nyasi wanapokusanyika katika sehemu zilizoungua hivi karibuni. Kwa vimelea vinavyosambazwa katika mazingira vilivyo na njia za uambukizaji zinazohusishwa na muundo wa uotaji wa mimea, moto unapaswa kuwa na athari za moja kwa moja kwa vimelea, pamoja na athari zisizo za moja kwa moja zinazotokana na wanyama kula mimea, ambapo inaweza kuathiri uingizaji na mfichuo wa vimelea katika mazingira. Tuliunganisha majaribio na takwimu za uchunguzi katika Hifadhi ya Taifa ya Serengeti ili kuchunguza athari za moja kwa moja na zisizo za moja kwa moja za moto kwa vimelea. Tulitathmini athari za moja kwa moja za moto kwa kupima mabadiliko ya idadi ya mabuu ya vimelea vya minyoo kwenye safu ya nyasi kabla na baada ya moto katika jozi ya viwanja vilivyochomwa na visivyochomwa. Ili kuchunguza athari zisizo za moja kwa moja zinazohusishwa na ulaji wa mimea baada ya moto, tulichukua sampuli za vinyesi vya wanyama walao nyasi, uzito wa nyasi, jotoridi la ardhini, na msongamano wa mabuu ya vimelea kila mwezi kwa muda wa miezi mitano kufuatia moto katika jozi saba za maeneo ya ufuatiliaji yaliyoungua na ambayo hayajachomwa. Hatimaye, ili kutathmini kama mabadiliko yanayotokana na moto kwa msongamano wa mabuu ya vimelea yaliathiri kiwango cha maambukizi kwa wanyama, tulikusanya sampuli za vinyesi kutoka kwa Swala Granti (Nanger granti), kila mwezi kwa miezi mitano ili kukadiria kiwango cha vimelea ndani ya mnyama. Moto uliua mabuu yote ya vimelea na kuongeza kiwango cha vinyesi vya wanyama kwa 40% kwa muda wa miezi miwili baada ya moto. Ongezeko la vinyesi baada ya moto lilisababisha kurudi upya kwa mabuu ya vimelea kwenye sehemu zilizoungua, lakini ulaji wa nyasi kwa wingi ulipelekea nyasi kuwa fupi na msongamano wa mabuu ulihusishwa na mabadiliko ya jotoridi la ardhini yanayohusishwa na kiwango cha nyasi na halijoto iliyopo. Swala Granti walikuwa na kiwango cha chini cha vimelea walipochukuliwa sampuli katika maeneo yaliyoungua sana ukilinganisha na maeneo yaliyoungua kidogo. Moto na ulaji wa nyasi baada ya moto hubadilisha msongamano wa mabuu ya vimelea katika mazingira na kugawanya mandhari katika maeneo yaliyochomwa moto na yasiyochomwa moto yenye hatari tofauti za maambukizi kwa wanyama walao nyasi wanaopatikana katika eneo husika. Athari zisizo za moja kwa moja zilizohesabiwa hapa zinawakilisha matokeo mapya yenye athari kubwa kwa mifumo yote ya malisho iliyoathiriwa na moto.

This study is the first to simultaneously evaluate whether (1) community saturation can require lengthy timespans to be reached and (2) there is a limit to the number of ecological strategies that can coexist. Determining if these ideas are supported is fundamental for better understanding the possible outcomes of species invasions and climate change.

Abstract

Determining if ecological communities are saturated (have a limit to the number of species they can support) has important implications for understanding community assembly, species invasions, and climate change. However, previous studies have generally been limited to short time frames that overlook extinction debt and have not explicitly considered how functional trait diversity may mediate patterns of community saturation. Here, we combine data from biodiversity surveys with functional and phylogenetic data to explore if the colonisation events after the Great American Biotic Interchange (closure of the Panamanian Isthmus) resulted in increases in species richness of communities of the snake family Dipsadidae. We determined the number and the direction of dispersal events between Central and South America by estimating ancestral areas based on a Bayesian time-calibrated phylogenetic analysis. We then evaluated whether variation in community saturation was mediated by the functional similarity of six traits for the resident and colonizing snakes and/or local environmental conditions. We found that colonised communities did not support more species than those that were not colonised. Moreover, we did not find an association between the functional diversity across sites and whether they were colonised by members from the lineages dispersing across the Isthmus or not. Instead, variation in species richness was predicted best by covariates such as time since colonisation and local environment. Taken together, our results suggest that snake communities of the Dipsadidae across the neotropics are saturated. Moreover, our research highlights two important factors to consider in studies of community saturation: extinction debt and the functional differences and similarities in species' ecological roles.

Resumen

Determinar si las comunidades ecológicas están saturadas (si tienen un límite en el número de especies que pueden albergar) tiene importantes implicaciones para entender el ensamblaje de comunidades, las invasiones de especies y el cambio climático. Sin embargo, los estudios previos en esta área se han limitado generalmente a marcos temporales cortos, ignorando el concepto de deuda de extinción y no considerando explícitamente cómo la diversidad de rasgos funcionales puede mediar en los patrones de saturación de las comunidades. En este trabajo combinamos datos publicados de muestreos de campo con datos funcionales y filogenéticos para explorar si los eventos de colonización después del Gran Intercambio Biótico Americano (ocurrido con el cierre del istmo de Panamá) resultaron en aumentos en la riqueza de especies de las comunidades de la familia de serpientes Dipsadidae. Determinamos el número y la dirección de los eventos de dispersión entre América Central y América del Sur mediante la estimación de áreas ancestrales basada en un análisis filogenético Bayesiano calibrado en el tiempo. Luego evaluamos si la variación en la saturación de las comunidades estaba mediada por la similitud funcional de seis rasgos para las serpientes residentes y colonizadoras y/o por las condiciones ambientales locales. Encontramos que las comunidades colonizadas no contienen más especies que aquellas que no fueron colonizadas. Además, no encontramos ninguna relación entre la diversidad funcional de los sitios considerados y el hecho de que estuvieran colonizados o no por miembros de los linajes que se dispersaron a través del Istmo. En cambio, la variación en la riqueza de especies se predijo mejor por covariantes como el tiempo transcurrido desde la colonización y el clima local. En conjunto, nuestros resultados sugieren que las comunidades de Dipsadidae a lo largo del neotrópico están saturadas. Además, nuestra investigación destaca dos factores importantes a considerar en los estudios de saturación de comunidades: la existencia de una deuda de extinción y las diferencias y similitudes funcionales en los papeles ecológicos de las especies.