Conservationists are happy when there are many tadpoles in a pond. Yet at high density, tadpoles are stressed; they need longer to develop, are smaller at metamorphosis, and survive less well as juvenile toads. To reduce the density stress, we need to build larger ponds.
A high number of tadpoles in a pond is pleasing but can cause density stress. Using an experimental approach with the natterjack toad, we show that such density stress extends the larval period up to threefold. Extending the larval period increases the risk of failing to reach metamorphosis before the pond dries up. Also, at high densities the tadpoles are more than 50 percent smaller—and on land small toads survive poorly.
For the highly endangered natterjack toad, these findings are particularly problematic. To reduce density stress for this species, it is important to build large ponds (ideally with an area larger than 100 m²). Also, these ponds should dry up, but not until autumn. This can be achieved by building drainable ponds.
Our findings are also important for population monitoring. In a pond with high tadpole density, the tadpoles are present throughout the summer, providing evidence of reproduction. In a pond with low tadpole density, the tadpoles reach metamorphosis after just 20 days. As a consequence, reproduction may go undetected.
Animals that reproduce once a year during a short breeding season need to get the timing right. Breed too early and the offspring might be exposed to harsh conditions, breed too late and the offspring might not be able to grow enough to survive the first winter. Generally, one of the major factors determining the timing of breeding is the environment. Therefore, due to climate change, we can expect shifts in the timing of breeding and indeed, various studies show that a shift towards earlier breeding in many animal species can be observed globally. This applies also to amphibian species, but in their case, not much is known about populations living at high elevations. We decided to fill this knowledge gap by looking at how the timing of breeding has shifted in the past 40 years in a population of common toads (Bufo bufo) which lives at almost 2000 masl in the Swiss Alps, just below the Grosse Scheidegg (Figure 1). We expect temperatures and amount of snow cover to play an important role. In fact, only once the snow melts and the breeding pond unfreezes can the toads emerge from hibernation belowground and successfully breed.
Figure 1. Breeding site of our focal population. The pond is located at around 1850 masl, and every year in spring it hosts a large number of common toads, grass frogs (Rana temporaria), and alpine newts (Ichthyosaura alpestris) attempting to breed.
Our results matched our expectations. We found that the warm temperatures and low amount of snow in winter and spring were associated with an earlier breeding. Interestingly, both temperature and snow cover have not been changing necessarily as expected over the past forty years at our study site. We observe great year to year variability, and to this day we can observe both late breeding (mid-late June) and early breeding (late April). Despite this great variability, breeding on average occurs earlier than in the 1980s (Figure 2), with an advancement of about 30 days. Further details and information can be found in our article “Four decades of phenology in an alpine amphibian: trends, stasis, and climatic drivers” published in the diamond Open-Access Peer Community Journal (doi.org/10.24072/pcjournal.240)
Figure 2. Trends of breeding phenology over the study period (1982–2021). (A) First day of the breeding season (day of the year, where January 1st = 1) and (B) date of peak breeding (i.e., date where the highest number of toads were observed in a given breeding season).
Climate change changes temperature and rainfall patterns, particularly in tropical environments, resulting in consequences for the persistence of wildlife populations. However, the complexities of the effects of changing temperature and rainfall on tropical mammals is not well studied. Together with our colleagues, we studied the demography of the gray mouse lemur in western Madagascar using data collected by the German Primate Center between 1994 and 2020. Climate trends in the lemur’s environment show declining rainfall over the wet season and increasing temperatures in the dry season. These climate trends, we found, led to decreased survival rates as well as increased reproductive rates. The competing demographic trends have prevented population collapse, but have destabilized the population by further speeding up their life cycle which was already one of the fastest among primates. Population projections into the next five decades suggest that when recently observed temperature and rainfall conditions persist, the population size of lemurs may continue to fluctuate, putting the population at increased risk of extinction. Our results show how, even though short-lived mammal species with high reproductive rates are expected to rapidly adapt to changes in their environment, such species can still face threats of extinction from climate change.
Nice and easily accessible summary of the latest paper on African wild dog dispersal and connectivity across the Kavango-Zambesi Transfrontier Conservation Area.
The diversity of bird communities in the Swiss Alps is declining more and more, a joint study of the University of Zurich and the Swiss Ornithological Institute has found. An analysis of data from the past two decades has revealed a loss of functional and compositional diversity in Alpine bird communities. This trend is likely connected to rising temperatures and changes in land use.
Ecologists believe that global climate change has had a particularly strong impact on animals and plants living in alpine regions, with expected changes in the distribution, abundance and interaction of species. There is evidence that the habitats of some bird species in Switzerland – such as the tree pipit or the European pied flycatcher – have shifted to higher altitudes in the past two decades. However, the impact of these changes on the composition of bird communities was previously unknown.
Our new study, in collaboration with the Swiss Ornithological Institute (Vogelwarte) has shed new light on this issue. Our study, which is based on two decades’ worth of data collected by volunteer ornithologists, reveals a downward trend. We found that bird communities in the Swiss Alps are undergoing a process of biotic homogenisation; in other words, birds living in this region are becoming less and less diverse.
The crossbill is one of the most functionally distinctive species included in the study. (photo by Valentin Graf)
Functional diversity is important One of the most obvious and simplest ways to measure the diversity of bird communities is by the number of species living in them. However, beyond species richness, the functional diversity of a certain community also provides valuable information. “Different species use resources and interact with the environment in different ways,” says first author, Vicente García-Navas. “Not all species play the same role in an ecosystem. The loss of a given species can be more detrimental than that of several others.” Specialists such as some woodpecker species are particularly important. The holes that they make are used for nesting and as hiding places by other birds and small mammals.
To quantify this functional diversity of bird communities, we compiled information on 100 traits characterising, among other things, the body mass, diet and habitat of each species. This enabled us to examine how the functional diversity of communities changes along the altitudinal gradient and to determine the trend over the past two decades.
High-altitude specialists on the edge Our analyses suggest that the upper forest boundary represents a functional barrier between two distinct groups. One group comprises the lowlands dominated by agriculture landscape and high mountain forests, where species such as the yellowhammer, the common whitethroat and the blackcap live. The other is composed of alpine communities, whose species are adapted to life in the open habitats above the treeline. For example, these species eat fewer caterpillars and build their nests on the ground, such as the rock ptarmigan.
However, the data analyses revealed that functional diversity of Alpine bird communities has decreased over the past few years. “Our study shows that mountain specialists are under increasing risk of becoming misfits,” says co-author Arpat Ozgul. The combined effects of habitat shrinkage, impossibility to find optimal habitats at higher elevations, and upward invasion by generalists are critical factors for these species.
The rise of generalist species This increase in generalist species such as the robin or the European pied flycatcher might also be a reason for the downward trend in the level of variation, or beta diversity, among communities. Our study also found that Alpine bird communities are becoming more and more redundant, with less variation.
“Overall, the study’s results suggest that the joint effect of global warming and land-use changes are boosting an impoverishment of bird communities in the Alps,” says García-Navas. This promotes shrub encroachment and is pushing the treeline upwards, which requires urgent conservation and management actions.
Many animals have evolved life cycles and strategies (patterns of survival and reproduction) in line with predictable seasonal variation in environmental conditions. Short and mild summers produce bursts of vegetation and food, the perfect time to give birth to young. Long, harsh winters when food is scarce have shaped animals to largely depend on fat reserves for energy, and in extreme cases, to hibernate or migrate.
However, climate change is altering these seasonal conditions to which many species are adapted. Temperatures are increasing, winter snowfall is declining, snow is melting earlier, summers are extending, and the frequency of extreme events (e.g., droughts, floods) are on the rise.
Our study, published in the Proceedings of the National Academy of Sciences USA (July 6 2020), found that marmot survival is affected differently by climate change during summer and winter seasons.
In this research, we analysed 40 years of life-history data, collected at the Rocky Mountain Biological Laboratory in Colorado, to understand how yellow-bellied marmots (large burrowing ground squirrels) have responded to climate change during their active summer season and the long winter hibernation.
Dr. Line Cordes, lead author from the School of Ocean Science at Bangor University: “Yellow-bellied marmots are a key indicator species for disentangling the seasonal impacts of climate change as they have a very distinct seasonal life history. They are found in western North America where climate change is more evident than anywhere else on the continent (with exception of the Arctic). Although they are a large rodent (reaching up to 6.5 kg), they are too small to remain active during winter and therefore hibernate for approximately 8 months. Marmots depend on energy stores acquired over the summer, and particular conditions to remain in deep torpor, which lowers energetic costs. Despite hibernation being an effective survival strategy in harsh environments, marmots can still lose up to 40% of their body weight.”
Over the course of four decades (1979-2018), marmot survival generally increased during summer but decreased during winter, and these effects were greatest among pups and one-year-olds.
Climate change at the study site has resulted in warmer winters with less snowfall, and warmer, drier summers which have become significantly longer in duration. Despite the similar seasonal survival trends across pups, one-year-olds and adults, the environmental factors driving these trends differed between the age-classes and seasons. For example, pup summer survival was higher following winters with reduced snowfall, possibly as mothers of these pups were in better condition during pregnancy and while caring for the pups as forage plants appeared sooner due to an earlier snow melt. Winter survival was lower following long, dry summers, most likely as pups were in poorer condition going into hibernation.
Dr. Arpat Ozgul, senior author of the study from the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, said: “The effects of climate change on the fate of a population are determined by the complex interactions of individuals with their biological and physical environment. Our study shows that we need to characterize these complex interactions accurately in order to predict the ultimate effect of climate change on the fate of a population. Critically our findings highlight the care that should be taken in drawing conclusions from annual survival responses to climate change, as this may be a misinterpretation, simplification or even underestimation of the actual more complex responses that can differ dramatically across different times of the year.”
Until now climate change has affected marmot survival positively during the summer months while leaving marmots more vulnerable during winter hibernation. Overall, the net change in survival was negative for pups, positive for yearlings, while there was no change for adults. It is important to note that continued climate change may change the patterns we observed in summer survival, as the persistence of forage plants would ultimately be impacted by progressively warmer and drier summers. Indeed, no marmot population is found in persistently warm and dry habitats.
The fact that climate change may benefit certain species during one season while resulting in unfavorable conditions during another season has potentially wide-ranging consequences across other species occupying temperate to more extreme habitats, such as deserts, mountains and polar regions, where the most rapid changes in climate are being observed. For wildlife living near the poles or near mountain tops, like marmots, there is nowhere to go when environmental conditions become less suitable.
Dr. Line Cordes added: “Social, burrowing, herbivorous mammals, like marmots, play an important role in ecosystem function as they help shape important habitats, and serve as prey for many predators. The loss or decline of these species would likely have wider reaching implications for biodiversity of montane habitats.”
The research was carried out by scientists from Bangor University and the Universities of California Los Angeles, Kansas, Sheffield, Rhode Island, Ottawa, Florida, Zurich, and Chicago Botanic Garden. This research would not have been possible without Ken Armitage who initiated and led this project from the early 1960’s – one of the longest running mammalian studies. We would also like to thank all the “marmoteers” who contributed to long-term data collection. Nor would it have been possible without Billy Barr and the Rocky Mountain Biological Laboratory for the long-term collection of local environmental data. The study has been funded by the Swiss National Science Foundation, the National Geographic Society, UCLA, a Rocky Mountain Biological Laboratory fellowship, and NSF.
“…The scope of the workshop is to investigate several aspects of animal movement and spatial use and to relate them to newest challenges in wildlife management and conservation…”
10–15 January 2021
Faido, Ticino, Switzerland
Understanding how animals respond to human-induced degradation and fragmentation of suitable habitats is critical for developing appropriate management and conservation plans. New technologies have made it possible to collect animal location data and remotely sensed environmental data at finer spatial and temporal scales. This workshop will provide participants with a quantitative toolset to leverage these data sources so that they can address emerging questions in the field of animal movement ecology.
During day one, participants will learn how to source landscape information through freely available remote sensing imagery and to import, manipulate, and represent georeferenced environmental data in R. Environmental data may represent ecological (e.g. habitat types, topography) or human activities (e.g. landscape use, settlements distribution). The aim of day one is to give participants a toolset that enables them to obtain and prepare environmental information that can be used to understand and explain animal movement patterns and space use.
Day two will be dedicated to the decomposition of movement trajectories and characterization of movement modes and phases. Participants will be exposed to the concept of net-squared displacement, an analytical method used to classify movement trajectories into alternative modes such as sedentarism, nomadism, dispersal, and migration. These statistics can be fed into generalized linear mixed models to investigate the factors responsible for the emergence of such patterns.
During day three, participants will be exposed to methods commonly used to quantify animal home ranges; the pros and cons of these methods will also be discussed. Alternative methods such as minimal convex polygons, kernel density estimators, local convex hulls, and brownian bridges will be presented. Particular attention will be given to the temporal scale of the analysis and on the environmental and anthropogenic factors that influence home ranges.
During the next day, we will use presence/absence data to analyze habitat selection and create species distribution models. Participants will be exposed to the most common methods used to investigate habitat preferences such as resource-selection functions, step-selection functions and integrated step-selection functions. Assumptions and limitations of each method will be addressed.
Finally, during the last day, participants will discover how to apply what they learned during the first four days of the workshop to develop evidence-based recommendations for the management of their study subject. In particular, participants will learn how to create various connectivity maps. Connectivity between populations is one of the most important aspects in the management of wild population in human-dominated landscapes. Lastly, we will discuss new research avenues and research gaps that will need to be addressed in the future for the integration of the spatial dimension in the conservation and management of animal species.
For additional information and registration please contact Gabriele Cozzi at gabriele.cozzi@uzh.ch
This workshop is supported through funding by the UZH Graduate Campus
Please note: the date may be changed due to the current Corona virus situation
Masai giraffes are the world’s tallest herbivores and beloved by people around the globe, but were recently classified as an endangered species by the International Union for Conservation of Nature (IUCN). New research published in Oecologia showed how food, predators, and people all influence giraffe social behavior. In particular, the international team of researchers from University of Zürich and Penn State University pinpointed the special requirements needed by mother giraffes to keep their babies safe, which can help land managers to protect the places most important for giraffes.
Giraffes foraging in Tarangire National Park, Tanzania
“Like all herbivores, giraffes need to find quality food to survive, but also need to avoid lions, or at least see them coming,” noted Monica Bond, PhD candidate at the Department of Evolutionary Biology and Environmental Studies, University of Zürich, member of the Population Ecology research group, and lead author of the paper. “Giraffes in our huge, unfenced study area can choose from among many different places to spend their time – places with different kinds of trees and bushes, and places deep inside protected parks or closer to farming towns or ranchlands where people live. There are lots of options in this landscape, including fewer lions outside the parks versus inside. So we wondered, how do these options influence giraffe grouping behavior? These data help us know what places are most important for these magnificent animals.” The study found that groups composed of adult giraffes were food-focused, not affected by predation risk. Adults formed the largest groups, up to 66 individuals, in the rainy season when food is plentiful, but smaller groups during the dry season when food is harder to find. In contrast, predation risk was a very important factor influencing congregations with calves.
Lions are the major predators of giraffe calves
“Giraffe calves are vulnerable to being killed by lions and other carnivores, while adults are typically large enough to escape predation,” stated senior author Barbara König, professor at the University of Zürich. “We were testing hypotheses about mother and calf behavior to see if their strategy was for calves to hide in thick bushes to avoid predators, be in the open to see predators coming, or be in large groups for many eyes and lower individual risk.” The researchers documented that in areas with the most lions, groups with calves were found more often in dense bushes than open grasslands, and those groups were smaller in size. This suggests giraffe mothers and calves have a strategy of hiding in dense bushes, rather than staying in open areas to better see lions, or gathering in large groups to dilute the predation risk. These results mean that dense bushlands are important habitat for giraffe calves and should be protected. Some cattle ranchers promote shrub removal to encourage grass for their livestock, but they share the rangelands with giraffes and other browsers that use shrubs.
The study also explored the influence of humans on giraffe grouping behaviors. “Outside the parks the human population has been rapidly expanding in recent years,” said Derek Lee, associate research professor of biology at Penn State University and co-author of the study. “Therefore, we felt it was important to understand how human presence affected grouping behavior, as natural giraffe habitat is ever-more dominated by people.” Interestingly, adult females with calves were more likely to be found closer to traditional pastoralist compounds called bomas, made by livestock-keeping, non-farming people. “We suspect this is because the pastoralists may disrupt predator behaviors to protect their livestock—and this benefits the giraffe calves,” noted Lee. Conversely, calf groups avoided areas close to farming peoples’ towns, suggesting a difference between traditional bomas versus more densely populated human settlements for giraffe mothers seeking food and safety for themselves and their calves.
Giraffes congregating on the shore of Lake Manyara National Park, Tanzania
“We were happy to find that traditional human settlements by ranchers appear to be compatible with the persistence of giraffe populations,” stated Bond. “But on the other hand, disturbances around towns likely represent a threat and should be limited in areas favored by giraffes.” The study was part of the world’s largest giraffe research project and used data from six years of systematic seasonal surveys across a 2,000 square kilometer area. The University of Zürich’s Population Ecology research group and its collaborators are at the forefront of giraffe conservation science. Learn more about giraffe research and conservation at http://www.wildnatureinstitute.org/giraffe.html
At present only in Swiss German, the English version will follow soon. For now, if you do not understand Swiss German, just lay back and enjoy some beautiful footage, of an amazing species 🙂
Our ‘little earth man’ Nino, (please pass me the translation from the German form, Erdmännchen), has done it! He has left the natal group.
Nino has successfully defended his PhD thesis at the end of November and is now ready for a new adventure…out there.
Typically meerkats disperse in small coalitions of two or more individuals, for they find strength in the number. Our previous dispersing trio proves it! Nino went alone, which is quite unusual for meerkats. So he may come back home, like the majority of the single dispersers or, being a very resilient disperser, he may also be successful alone elsewhere. According to what is written in his thesis (shall we really trust his work…?), the task will now be to find some conspecifics of the opposite sex and a territory to settle…
