Bat responses to aridity

ABSTRACT Due to the perceived low biodiversity of arid environments, species inhabiting these regions have received less research compared to tropical areas and biodiversity hotspots. However, arid conditions are predicted to characterise a larger number of regions globally and there is a greater need to identify strategies that allow species to survive in these harsh environments. Bats occupy a wide variety of habitats, including some of the most arid habitats on Earth, thanks also to their nocturnal habits, ability of powered flight and species-specific physiological adaptations. However, knowledge of the mechanisms in place to face the variety of stressors linked with aridity is still relatively scarce, particularly concerning behaviour and in the light of the diversity characterising bats as a group. In this thesis, I investigate further the responses and strategies that bats employ to cope with aridity, with a particular focus on the role of functional traits and movement. First, I model functional trait variation of bat assemblages to identify trends along the gradient of aridity globally. Bat assemblages inhabiting conditions of higher aridity display morphological and echolocation features more suitable to move in open habitats thanks to the greater speed and cost efficiency of flight. Additionally, larger body sizes appear to be favoured at these conditions, potentially as an advantage to reduce the exposure to cutaneous evaporative water loss by retaining a lower surface-to-volume ratio. Despite these general trends, bat communities in arid environments still retain functional diversity, with manoeuvrable species taking benefit from their ability to hunt in the vicinity of the vegetation. Therefore, I then investigate how a low-mobility species, Lavia frons, copes with seasonal changes in aridity and the associated reduction in resources by following its movement using miniaturised GPS devices across a rainy and a dry season. Despite the overall low mobility observed, L. frons appears to respond to seasonal increases in aridity by moving over larger areas and for extended periods of time, supporting the role of movement as a strategy to offset for low prey densities during harsh periods. Finally, due to the lack of synthesis on the topic of bat responses to aridity, I propose a narrative review integrating current available knowledge and thus providing an overview to facilitate future research. In my literature review, I cover both physiological and behavioural mechanism, pinpointing gaps in knowledge and the need of more direct studies on behaviour. Additionally, I discuss potential trade-offs among responses, focusing on the role of movement and roosting conditions in mediating the impact of environmental stressors. This thesis brings advances in the study of bat responses to aridity, targeting some of the knowledge gaps present in the literature and setting the ground for further research. My results also highlight the importance of taking into account the interactions between physiological and behavioural mechanisms, as well as environmental conditions, when approaching the study of bat responses to aridity.TIIVISTELMÄ Kuivien ympäristöjen lajeja on tutkittu vähemmän kuin trooppisten alueiden lajeja. Kuivia elinympäristöjä esiintyy maapallolla kuitenkin laajalti ja siksi on tärkeää tietää miten eliöt säilyvät näillä karuilla alueilla hengissä. Lepakot elävät monenlaisissa elinympäristöissä. Osa niistä on maapallon kuivimpia, mutta niissäkin lepakot selviytyvät yöaktiivisuutensa, hyvän lentotaitonsa ja fysiologisten sopeutumiensa ansiosta. Mekanismit, etenkin käyttäytymiseen liittyvät, joiden turvin lepakot noilla alueilla selviävät tunnetaan kuitenkin melko puutteellisesti. Tässä väitöskirjassa tutkin millaisia vasteita ja strategioita lepakoilla on kuivuuteen liittyen. Erityisenä kiinnostuksen kohteena on selvittää, mikä on toiminnallisten piirteiden ja liikkumisen merkitys. Ensin mallinnan lepakkoyhteisöjen toiminnallisten piirteiden vaihtelua selvittääkseni kuivuuden merkitystä laajassa mittakaavassa. Kuivien alueiden lepakkoyhteisöillä on sellaisia rakenteellisia ja kaikuluotaukseen liittyviä piirteitä, jotka sopivat avoimilla alueilla liikkumiseen ja saalistukseen. Näiden ansiosta niiden lento on nopeaa ja kustannustehokasta. Kuivissa oloissa valinta näyttää suosivan myös isompaa ruumiin kokoa, luultavasti siksi että se vähentää veden haihtumista. Näistä yleisistä suuntauksista huolimatta kuivien alueiden lepakkoyhteisöjen toiminnallinen monimuotoisuus säilyy, ja kyvykkäimmät lajit hyötyvät kyvystään saalistaa kasvillisuuden lähellä. Tutkin pienien satelliittipaikantimien avulla miten vähän liikkuva Lavia frons-laji selviytyy kun käytettävissä olevien resurssien määrä vaihtelee kuivien ja sadekausien välillä. Heikosta liikkumiskyvystään huolimatta L. frons liikkui laajemmalla alueella ja pidempiä aikoja kuivina aikoina kuin sadekausina. Tällä tavalla eläimet kykenivät tavallaan kompensoimaan kuivien kausien alhaiset saalistiheydet. Lepakoiden vasteista kuivuuteen ei tätä ennen ole tehty synteesiä. Kirjallisuuskatsauksessani käsittelen fysiologiaan ja käyttäytymiseen liittyviä mekanismeja ja tunnistan ne käyttäytymiseen liittyvät aiheet, joista tarvitaan vielä lisätutkimuksia. Lisäksi käyn läpi potentiaalisia kanssakäyntejä, keskittyen erityisesti siihen, että mikä rooli liikkumiseen ja lepopaikkoihin liittyvillä olosuhteilla on ympäristöstä johtuvien stressitekijöiden hallinnassa. Tämä väitöskirja on edistysaskel sen selvittämisessä, että miten lepakot reagoivat kuivuuteen. Tässä tutkimuksessa on paneuduttu nykytiedoissa olleisiin aukkoihin ja samalla luotu pohjaa uusille tutkimuksille. Tulokseni korostavat, että kuivuuden vaikutuksia tutkittaessa on tärkeää huomioida fysiologisten ja käyttäytymiseen liittyvien mekanismien vuorovaikutukset ympäristötekijöitä unohtamatta

Species richness patterns and functional traits of the bat fauna of arid southern Africa

The bat fauna of arid regions is still poorly studied mostly due to a lack of interest in areas with low species richness and a low number of threatened species. In this study, we reviewed the status of bat diversity in the arid parts of southern Africa, with the aim of setting up a baseline for future work. In particular, we described species richness patterns across four arid zones within the region (Namib Desert, Kalahari, Nama Karoo and Succulent Karoo), exploring abiotic gradients and local landscape structure. Additionally, we examined bat functional groups in this region and compared them with those of three other arid regions of the world to identify potential similarities and differences. The southern African arid region hosted 17 bat species, representing eight families, of which three are endemic to the region (Rhinolophus denti, Laephotis namibensis and Cistugo seabrae) and one is vagrant (the fruit bat Eidolon helvum). Species richness varied spatially within this arid region, being highest in the drier but topographically heterogeneous Namib Desert, probably as a result of roost availability. With regards to functional groups, the southern African arid region had few bat species adapted to foraging in open spaces, particularly when compared with the neighbouring savannahs. Drawing from this study, we suggest that: a) despite species richness decreasing with increasing aridity at the sub-continental scale, at a more local scale landscape features (e.g. habitat structure) might be more relevant than aridity in determining bat species richness; and b) an unknown factor, possibly patterns of temperature limiting the availability of insects flying high above the ground, restricted the diversity of the open air foragers throughout the region. We highlight additional areas of research worth investigation.Peer reviewe

Global patterns of functional trait variation along aridity gradients in bats

Aim Our understanding of the biological strategies employed by species to cope with challenges posed by aridity is still limited. Despite being sensitive to water loss, bats successfully inhabit a wide range of arid lands. We here investigated how functional traits of bat assemblages vary along the global aridity gradient to identify traits that favour their persistence in arid environments. Location Global. Time period Contemporary. Major taxa studied Bats. Methods We mapped the assemblage-level averages of four key bat traits describing wing morphology, echolocation and body size, based on a grid of 100-km resolution and a pool of 915 bat species, and modelled them against aridity values. To support our results, we conducted analyses also at the species level to control for phylogenetic autocorrelation. Results At the assemblage level, we detected a rise in values of aspect ratio, wing loading and forearm length, and a decrease in echolocation frequency with increasing aridity. These patterns were consistent with trends detected at the species level for all traits. Main conclusions Our findings show that trait variation in bats is associated with the aridity gradient and suggest that greater mobility and larger body size are advantageous features in arid environments. Greater mobility favours bats' ability to track patchy and temporary resources, while the reduced surface-to-volume ratio associated with a larger body size is likely to reduce water stress by limiting cutaneous evaporation. These findings highlight the importance of extending attention from species-specific adaptations to broad scale and multispecies variation in traits when investigating the ability of species to withstand arid conditions.Peer reviewe

Movement seasonality in a desert-dwelling bat revealed by miniature GPS loggers

Background Bats are among the most successful desert mammals. Yet, our understanding of their spatio-temporal dynamics in habitat use associated with the seasonal oscillation of resources is still limited. In this study, we have employed state-of-the-art lightweight GPS loggers to track the yellow-winged bat Lavia frons in a desert in northern Kenya to investigate how seasonality in a desert affects the a) spatial and b) temporal dimensions of movements in a low-mobility bat. Methods Bats were tracked during April-May 2017 (rainy season) and January-February 2018 (dry season) using 1-g GPS loggers. Spatial and temporal dimensions of movements were quantified, respectively, as the home range and nightly activity patterns. We tested for differences between seasons to assess responses to seasonal drought. In addition, we quantified home range overlap between neighbouring individuals to investigate whether tracking data will be in accordance with previous reports on territoriality and social monogamy in L. frons. Results We obtained data for 22 bats, 13 during the rainy and 9 during the dry season. Home ranges averaged 5.46 +/- 11.04 ha and bats travelled a minimum distance of 99.69 +/- 123.42 m/hour. During the dry season, home ranges were larger than in the rainy season, and bats exhibited high activity during most of the night. No apparent association with free water was identified during the dry season. The observed spatial organisation of home ranges supports previous observations that L. frons partitions the space into territories throughout the year. Conclusions Our results suggest that, in low-mobility bats, a potential way to cope with seasonally harsh conditions and resource scarcity in deserts is to cover larger areas and increase time active, suggesting lower cost-efficiency of the foraging activity. Climate change may pose additional pressures on L. frons and other low-mobility species by further reducing food abundances.Peer reviewe

Movement seasonality in a desert-dwelling bat revealed by miniature GPS loggers

Background Bats are among the most successful desert mammals. Yet, our understanding of their spatio-temporal dynamics in habitat use associated with the seasonal oscillation of resources is still limited. In this study, we have employed state-of-the-art lightweight GPS loggers to track the yellow-winged bat Lavia frons in a desert in northern Kenya to investigate how seasonality in a desert affects the a) spatial and b) temporal dimensions of movements in a low-mobility bat. Methods Bats were tracked during April-May 2017 (rainy season) and January-February 2018 (dry season) using 1-g GPS loggers. Spatial and temporal dimensions of movements were quantified, respectively, as the home range and nightly activity patterns. We tested for differences between seasons to assess responses to seasonal drought. In addition, we quantified home range overlap between neighbouring individuals to investigate whether tracking data will be in accordance with previous reports on territoriality and social monogamy in L. frons. Results We obtained data for 22 bats, 13 during the rainy and 9 during the dry season. Home ranges averaged 5.46 +/- 11.04 ha and bats travelled a minimum distance of 99.69 +/- 123.42 m/hour. During the dry season, home ranges were larger than in the rainy season, and bats exhibited high activity during most of the night. No apparent association with free water was identified during the dry season. The observed spatial organisation of home ranges supports previous observations that L. frons partitions the space into territories throughout the year. Conclusions Our results suggest that, in low-mobility bats, a potential way to cope with seasonally harsh conditions and resource scarcity in deserts is to cover larger areas and increase time active, suggesting lower cost-efficiency of the foraging activity. Climate change may pose additional pressures on L. frons and other low-mobility species by further reducing food abundances.Peer reviewe

Movement seasonality in a desert-dwelling bat revealed by miniature GPS loggers.

Background: Bats are among the most successful desert mammals. Yet, our understanding of their spatio-temporal dynamics in habitat use associated with the seasonal oscillation of resources is still limited. In this study, we have employed state-of-the-art lightweight GPS loggers to track the yellow-winged bat Lavia frons in a desert in northern Kenya to investigate how seasonality in a desert affects the a) spatial and b) temporal dimensions of movements in a low-mobility bat. Methods: Bats were tracked during April-May 2017 (rainy season) and January-February 2018 (dry season) using 1-g GPS loggers. Spatial and temporal dimensions of movements were quantified, respectively, as the home range and nightly activity patterns. We tested for differences between seasons to assess responses to seasonal drought. In addition, we quantified home range overlap between neighbouring individuals to investigate whether tracking data will be in accordance with previous reports on territoriality and social monogamy in L. frons. Results: We obtained data for 22 bats, 13 during the rainy and 9 during the dry season. Home ranges averaged 5.46 ± 11.04 ha and bats travelled a minimum distance of 99.69 ± 123.42 m/hour. During the dry season, home ranges were larger than in the rainy season, and bats exhibited high activity during most of the night. No apparent association with free water was identified during the dry season. The observed spatial organisation of home ranges supports previous observations that L. frons partitions the space into territories throughout the year. Conclusions: Our results suggest that, in low-mobility bats, a potential way to cope with seasonally harsh conditions and resource scarcity in deserts is to cover larger areas and increase time active, suggesting lower cost-efficiency of the foraging activity. Climate change may pose additional pressures on L. frons and other low-mobility species by further reducing food abundances

Movement seasonality in a desert-dwelling bat revealed by miniature GPS loggers

Background Bats are among the most successful desert mammals. Yet, our understanding of their spatio-temporal dynamics in habitat use associated with the seasonal oscillation of resources is still limited. In this study, we have employed state-of-the-art lightweight GPS loggers to track the yellow-winged bat Lavia frons in a desert in northern Kenya to investigate how seasonality in a desert affects the a) spatial and b) temporal dimensions of movements in a low-mobility bat. Methods Bats were tracked during April–May 2017 (rainy season) and January–February 2018 (dry season) using 1-g GPS loggers. Spatial and temporal dimensions of movements were quantified, respectively, as the home range and nightly activity patterns. We tested for differences between seasons to assess responses to seasonal drought. In addition, we quantified home range overlap between neighbouring individuals to investigate whether tracking data will be in accordance with previous reports on territoriality and social monogamy in L. frons. Results We obtained data for 22 bats, 13 during the rainy and 9 during the dry season. Home ranges averaged 5.46 ± 11.04 ha and bats travelled a minimum distance of 99.69 ± 123.42 m/hour. During the dry season, home ranges were larger than in the rainy season, and bats exhibited high activity during most of the night. No apparent association with free water was identified during the dry season. The observed spatial organisation of home ranges supports previous observations that L. frons partitions the space into territories throughout the year. Conclusions Our results suggest that, in low-mobility bats, a potential way to cope with seasonally harsh conditions and resource scarcity in deserts is to cover larger areas and increase time active, suggesting lower cost-efficiency of the foraging activity. Climate change may pose additional pressures on L. frons and other low-mobility species by further reducing food abundances.info:eu-repo/semantics/publishedVersio

Insular bats and research effort: a review of global patterns and priorities

Evidence-based knowledge is critical for the delineation and success of conservation interventions. However, despite limited research resources, research efforts frequently fail to target conservation priorities. Island endemic bats (IEBs) are a poorly studied group inhabiting some of the world's most vulnerable habitats, and for which no review of research allocation has ever been conducted. We conducted a bibliometric review to evaluate the global research patterns for IEBs with respect to individual species, geographical distribution and the International Union for Conservation of Nature (IUCN) Red List categories. Additionally, we studied the relationship between the number of publications and changes in Red List category, and identified species-based and area-based priorities for future research. IEBs are significantly more threatened than bat species that are not island endemics. However, research focusing on IEBs is scarce, centred on species of lesser conservation concern, and spatially asymmetric, overlooking areas of high IEB biodiversity. Conservation-oriented research seems to target species facing high extinction risk, but is extremely thinly and unevenly distributed. Although we found a positive association between research effort and improvement in Red List category, an increase in extinction risk did not trigger more scientific attention. A prioritisation analysis highlighted, as the top five islands for species richness in the least-studied and highest conservation concern IEBs: Sulawesi, Timor, New Guinea, Java, and Borneo. The ten species of highest research priority include threatened and Data Deficient species from Southeast Asian and Pacific islands. Conservation-oriented research seems to be too scarce to satisfy conservation needs. The observed mismatch between research allocation and conservation priorities may reflect the fact that highly endangered species are unattractive targets for fund-raising, due to species crypticity, high research budget requirements, and high risk of project failure. However, our findings support the importance of research for the conservation of IEBs, and we therefore advocate that more attention is directed towards the least-known species

Filling in knowledge gaps: new reports on distribution and ecological requirements for two Data Deficient East African bat species.

Efforts to sample bat biodiversity in Africa have been patchy, as reflected on the assessments of the IUCN, reporting 22% of the bat species in sub-Saharan Africa as Data Deficient[1]. This is also due to limited funding targeting these species since such projects retain relatively high risk of failure connected with field challenges and difficulties in locating the species. However, Data Deficient species are also claimed to be on average more threatened than fully assessed ones[2,3]. Therefore, accumulation of knowledge and its prompt sharing is critical for the implementation of conservation measures where needed. Here we report new records for two extremely rare and poorly known African bat species, Macinnes’s Mouse-Tailed bat Rhinopoma macinnesi and Hamilton’s Tomb Bat Taphozous Hamiltoni (both Data Deficient). These species are historically known only from very few locations in East Africa and their actual distribution, population abundances and ecological requirements are still unknown[1]. We recorded the presence of these species using mist-nets during three field expeditions conducted in 2016-2018 in Sibiloi National Park, norther Kenya, and its surroundings. We provide a description of habitat in the foraging sites for the two species. Additionally, we carried out further sampling of T. hamiltoni in 2018, recording echolocation calls and employing radio-tracking to identify roosting sites and estimate distance commuted between roost and foraging ground. Given the lack of recent reports of these species elsewhere, their presence in this area is of great relevance. However, despite the presence of Sibiloi National Park, these populations will likely be threatened in the future by rapid change in local climate, determined by anthropogenic exploitation of local water resources. We therefore recommend periodical monitoring to guarantee their persistence. [1]IUCN (2017). The IUCN Red List of Threatened Species. Version 2017-3. http://www.iucnredlist.org [2]Jetz W, Freckleton RP (2015) Towards a general framework for predicting threat status of data-deficient species from phylogenetic, spatial and environmental information. Philosophical Transactions of the Royal Society B-Biological Sciences 370: 20140016. [3]Bland LM, Bielby J, Kearney S, Orme CDL, Watson JE, Collen B (2017). Toward reassessing data‐deficient species. Conservation Biology, 31(3): 531-539.peerReviewe