In one of the largest field campaigns of its kind, we found that ecophysiological traits predicted species distributions for 116 species across four taxonomic groups across two elevational transects.

Abstract

Understanding the role of thermal tolerances in determining species distributions is important for assessing species responses to climate change. Two hypotheses linking physiology with species distributions have been put forward—the climatic variability hypothesis and the climatic extreme hypothesis. The climatic variability hypothesis predicts the selection of individuals with broad thermal tolerance in more variable climatic conditions and the climatic extreme hypothesis predicts the selection of individuals with extreme thermal tolerance values under extreme climatic conditions. However, no study has tested the predictions of these hypotheses simultaneously for several taxonomic groups along elevational gradients. Here, we related experimentally measured critical thermal maxima, critical thermal minima and thermal tolerance breadths for 15,187 individuals belonging to 116 species of ants, beetles, grasshoppers, and spiders from mountain ranges in central and northern Pakistan to the limits and breadths of their geographic and temperature range. Across all species and taxonomic groups, we found strong relationships between thermal traits and elevational distributions both in terms of geography and temperature. The relationships were robust when repeating the analyses for ants, grasshoppers, and spiders but not for beetles. These results indicate a strong role of physiology in determining elevational distributions of arthropods in Southern Asia. Overall, we found strong support for the climatic variability hypothesis and the climatic extreme hypothesis. A close association between species' distributional limits and their thermal tolerances suggest that in case of a failure to adapt or acclimate to novel climatic conditions, species may be under pressure to track their preferred climatic conditions, potentially facing serious consequences under current and future climate change.

The authors evaluated for the first time how anthropogenic habitat fragmentation can affect food chain length in highly diverse food webs. The authors found that bottom-up mass effects are important but also network structural changes driven by habitat modification have the potential to affect chain length.

Abstract

The food chain length represents how much energy reaches different trophic levels in food webs. Environmental changes derived from human activities have the potential to affect chain length. We explore how habitat area and edges affect chain length through: (1) a bottom-up effect of abundance (‘pyramid hypothesis’); (2) the truncation of the highest trophic level (‘trophic-rank hypothesis’); and (3) changes in species connectivity patterns (‘connectivity hypothesis’). We built plant-leaf miner-parasitoid food webs in 19 remnants of a fragmented Chaco forest from central Argentina. On each remnant, we constructed food webs from different locations at the forest interior and edges. For each food web, we registered the abundance of species, the species richness of each trophic level, estimated the connectivity of their networks, and the average food chain length. We used structural equation models to evaluate the direct and indirect effects of habitat area and edge/interior location on food chain length mediated by species richness, abundance and connectivity. We found no direct effects of habitat area on chain length but chains were longer at forest edges than at their interior. The three mechanisms were supported by our results, although they showed different strengths. First, we found that the interior favours a bottom-up abundance effect from herbivores to parasitoids that positively affected chain length; second, we found that the forest area positively affects plant richness, which has a strong effect on the number of resources used by consumers, with a positive effect on chain length. Third, the remnant area and interior position favoured plant richness with a negative effect on the abundance of parasitoids, which had a positive effect on chain length. In general, the strongest effects on chain length were detected through changes in abundance rather than species richness although abundance was less affected by habitat fragmentation. We evaluated for the first time the effects of human-driven habitat fragmentation on the length of trophic chains in highly diverse plant-herbivore-parasitoid networks. Despite the loss of species, small habitat fragments and edges embedded in the agricultural matrix can support interaction networks, making them conservation targets in managed landscapes.

Resumen

El largo de cadenas tróficas representa cuanta energía alcanza diferentes niveles tróficos en redes tróficas. Los cambios ambientales producto de las actividades humanas tienen el potencial de afectar el largo de las cadenas tróficas. Exploramos como el área de hábitat y los bordes afectan el largo de cadenas tróficas a través de: (1) un efecto ascendente de la abundancia (‘hipótesis pirámide’); (2) el truncamiento del nivel trófico superior (‘hipótesis de ranking trófico’); y (3) cambios en los patrones de conectividad (‘hipótesis de conectividad’). Construimos redes tróficas entre plantas-minadores de hoja-parasitoides en 19 remanentes de bosque Chaqueño serrano altamente fragmentado en el centro de Argentina. Para cada remanente construimos redes tróficas en distintas ubicaciones en el borde e interior del bosque. Para cada red trófica registramos la abundancia media de las especies, la riqueza de cada nivel trófico, estimamos la conectividad de las redes y el largo de cadenas tróficas promedio. Utilizamos modelos de ecuaciones estructurales para evaluar los efectos directos e indirectos del área y la ubicación borde/interior sobre el largo de cadenas tróficas mediado por la riqueza de especies, la abundancia y la conectividad. No encontramos efectos directos del área de hábitat sobre el largo de cadenas, pero las cadenas fueron más largas en los bordes que en el interior. Los tres mecanismos propuestos fueron apoyados por los resultados, pero mostraron distinta fuerza. Primero, encontramos que el interior de los bosques favorece los efectos ascendentes de la abundancia desde los herbívoros a los parasitoides lo que afectó positivamente al largo de las cadenas; segundo, encontramos que el área de bosque afectó positivamente a la riqueza de especies, lo que tuvo un efecto positivo en el largo de cadenas. Tercero, el área de bosque remanente y la ubicación en el interior favorecieron la riqueza de plantas, influyendo negativamente en la abundancia de parasitoides lo que tuvo un efecto positivo en el largo de cadenas. En general, los efectos más fuertes sobre el largo de cadenas se detectaron a través de cambios en la abundancia más que en la riqueza, aunque la abundancia fue menos afectada por la fragmentación del hábitat que la riqueza de especies. En este estudio evaluamos por primera vez los efectos de la fragmentación del hábitat por causas humanas sobre el largo de cadenas tróficas en redes tróficas altamente diversas de plantas, herbívoros y parasitoides. A pesar de la pérdida de especies, los fragmentos pequeños y los bordes de bosque inmersos en una matriz agrícola pueden sostener redes de interacciones, convirtiéndolos en objetivos de conservación en paisajes manejados.

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.