Mathieu Basille

Habitat–performance relationships: finding the right metric at a given spatial scale

The field of habitat ecology has been muddled by imprecise terminology regarding what constitutes habitat, and how importance is measured through use, selection, avoidance and other bio-statistical terminology. Added to the confusion is the idea that habitat is scale-specific. Despite these conceptual difficulties, ecologists have made advances in understanding ‘how habitats are important to animals’, and data from animal-borne global positioning system (GPS) units have the potential to help this clarification. Here, we propose a new conceptual framework to connect habitats with measures of animal performance itself—towards assessing habitat–performance relationship (HPR). Long-term studies will be needed to estimate consequences of habitat selection for animal performance. GPS data from wildlife can provide new approaches for studying useful correlates of performance that we review. Recent examples include merging traditional resource selection studies with information about resources used at different critical life-history events (e.g. nesting, calving, migration), uncovering habitats that facilitate movement or foraging and, ultimately, comparing resources used through different life-history strategies with those resulting in death. By integrating data from GPS receivers with other animal-borne technologies and combining those data with additional life-history information, we believe understanding the drivers of HPRs will inform animal ecology and improve conservation.

Selecting habitat to survive: The impact of road density on survival in a large carnivore

Habitat selection studies generally assume that animals select habitat and food resources at multiple scales to maximise their fitness. However, animals sometimes prefer habitats of apparently low quality, especially when considering the costs associated with spatially heterogeneous human disturbance. We used spatial variation in human disturbance, and its consequences on lynx survival, a direct fitness component, to test the Hierarchical Habitat Selection hypothesis from a population of Eurasian lynx Lynx lynx in southern Norway. Data from 46 lynx monitored with telemetry indicated that a high proportion of forest strongly reduced the risk of mortality from legal hunting at the home range scale, while increasing road density strongly increased such risk at the finer scale within the home range. We found hierarchical effects of the impact of human disturbance, with a higher road density at a large scale reinforcing its negative impact at a fine scale. Conversely, we demonstrated that lynx shifted their habitat selection to avoid areas with the highest road densities within their home ranges, thus supporting a compensatory mechanism at fine scale enabling lynx to mitigate the impact of large-scale disturbance. Human impact, positively associated with high road accessibility, was thus a stronger driver of lynx space use at a finer scale, with home range characteristics nevertheless constraining habitat selection. Our study demonstrates the truly hierarchical nature of habitat selection, which aims at maximising fitness by selecting against limiting factors at multiple spatial scales, and indicates that scale-specific heterogeneity of the environment is driving individual spatial behaviour, by means of trade-offs across spatial scales.

Plastic response of fearful prey to the spatiotemporal dynamics of predator distribution

Ecological theory predicts that the intensity of antipredator responses is dependent upon the spatiotemporal context of predation risk (the risk allocation hypothesis). However, most studies to date have been conducted over small spatial extents, and did not fully take into account gradual responses to predator proximity. We simultaneously collected spatially explicit data on predator and prey to investigate acute responses of a threatened forest ungulate, the boreal caribou (Rangifer tarandus), to the spatiotemporal dynamics of wolf (Canis lupus) distribution during spring. Movement analysis of GPS-collared individuals from both species revealed high plasticity in habitat-selection decisions of caribou. Female caribou avoided open areas and deciduous forests and moved relatively fast and toward foraging areas when wolves were closer than 2.5 km. Caribou also avoided food-rich areas only when wolves were within 1 km. Our results bridge the gap between long-term perceived risk and immediate flight responses by revealing dynamic antipredator tactics in response to predator proximity.

The production of soldiers and the maintenance of caste proportions delay the growth of termite incipient colonies

In a termite colony, the incipient phase is the most critical part of the life of the colony. The quality of the investment in the first offspring by the primary reproductives may determine the rate of success of the colony to survive the first year and its growth rate in the following years. However, termite colonies possess a physiological constraint, forcing the group to maintain a relatively fixed caste proportion. During the development of the incipient colony, there is therefore a conflict for the group on the developmental pathways of larvae into workers or soldiers. On the one hand, the more workers produced, the more work forces would be available to provide for the primary reproductives, the brood and the nest maintenance (overall nurturing capacity). On the other hand, some larvae must develop into soldiers to maintain the caste proportion, reducing the potential number of workers. Using incipient colonies of Coptotermes gestroi (Wasmann), we investigated the cost of maintaining the soldier proportion over the growth of the colony within the first year. Our results showed that an incipient colony maintains a stable soldier proportion regardless of the stress imposed. The resources redirected into the replacement of soldiers not only reduced the total number of workers, but it also reduced the overall growth of the colony by delaying the development of the remaining eggs. Our observations suggest that in termite incipient colonies, because of physiological constraints, the maintenance of the soldier proportion overrides the development of the colony.

Factors Affecting Beech Fagus sylvatica Bark Stripping by Red Deer Cervus elaphus in a Mixed Forest

Bark stripping by large herbivores is widespread, yet poorly understood. Our study was carried out in a 2000-ha area situated in the Vosges Mountains, France, where beech Fagus sylvatica bark is heavily bark stripped by red deer Cervus elaphus. We tested whether the seasonal variation in the frequency of beech bark stripping by red deer was correlated with bark nutritive value or bark mechanical properties (using an index of bark detachability). We also evaluated whether red deer selected beech trees based on the chemical composition of their bark (e.g. carbohydrates and minerals). Bark-stripped trees had slightly higher carbohydrate contents than non-stripped trees, but this difference resulted from a physiological reaction of the tree to bark stripping. Bark composition was similar between stripped and non-stripped trees spring and summer, but was easier to detach during these periods than during autumn and winter. Therefore, beech bark stripping by red deer in the Vosges Mountains does not appear to be driven by nutritional needs, but it may help deer in improving digestion efficiency.

Developmental Instability in Incipient Colonies of Social Insects

Social insect colonies can provide homeostatic conditions that buffer the incidence of environmental fluctuations on individuals, which have contributed to their ecological success. Coptotermes (Isoptera: Rhinotermitidae) is a highly invasive termite genus and several species have important economic impact in many areas of the world. Mature Coptotermes colonies with millions of individuals can provide optimal environmental condition and nurturing capacity for the developing brood. However, it was previously suggested that contrary to mature colonies, incipient colonies may be exposed to critical stress, which may explain for the low success rate of establishment within the first year of the life of a termite colony. We here investigated the stress imposed on individuals of incipient colonies by comparing the developmental instability of individuals between incipient and mature colonies of two Coptotermes species, C. formosanus Shiraki and C. gestroi (Wasmann). We assessed the developmental instability by measuring the asymmetry of morphological traits from the head capsule of the soldier caste. Soldiers from incipient colonies of both species displayed strong asymmetrical traits in comparison to soldiers from mature colonies. We suggest that homeostatic conditions for optimal development are reached as the colony matures, and confirmed that the incipient colony remains a critical bottleneck where individuals are exposed to high developmental stress.

Role of accelerated developmental pathway and limited nurturing capacity on soldier developmental instability in subterranean termite incipient colonies

In the subterranean termite Coptotermes gestroi (Wasmann), soldiers developing in incipient colonies display strong fluctuating asymmetry when compared with soldiers developing in mature colonies. This strong asymmetry may arise from two different types of stress factors on individuals. First, the accelerated development of nanitic (small) soldiers may impose a direct physiological stress as Coptotermes soldiers produced in incipient colonies have two less molting events than soldiers produced in mature colonies. Second, the environmental conditions in incipient colonies present a major constraint with limited access to resources and small numbers of workers to care for the developing brood. In this study, 459 soldiers from 73 incipient colonies (6-month-old) displaying only nanitic soldiers were investigated in a range of nurturing capacity scenarios. Nanitic soldiers developing in incipient colonies with high nurturing capacity displayed more symmetrical traits than the ones developing in colonies with low nurturing capacity. In addition, the first soldiers to emerge in the colony were the most asymmetrical individuals, showing that as the conditions improve rapidly with the growth of the colony, newly produced nanitic soldiers manifest the lessening of stress in normalization of their morphology. However, the nurturing capacity of the colony only partially explained the developmental instability variability, implying that the accelerated development of nanitic soldiers remains an important stress factor in incipient colonies, in comparison with soldiers developing in mature colonies with two additional molts and homeostatic environmental conditions.

Data Quality: Detection and Management of Outliers

Tracking data can potentially be affected by a large set of errors in different steps of data acquisition and processing. Erroneous data can heavily affect analysis, leading to biased inference and misleading wildlife management/conservation suggestions. Data quality assessment is therefore a key step in data management. In this chapter, we especially deal with biased locations, or ‘outliers’. While in some cases incorrect data are evident, in many situations, it is not possible to clearly identify locations as outliers because although they are suspicious (e.g. long distances covered by animals in a short time or repeated extreme values), they might still be correct, leaving a margin of uncertainty. In this chapter, different potential errors are identified and a general approach to managing outliers is proposed that tags records rather than deleting them. According to this approach, practical methods to find and mark errors are illustrated on the database created in Chaps. 2, 3, 4, 5, 6 and 7.

Tracking Animals in a Dynamic Environment: Remote Sensing Image Time Series

This chapter looks into the spatiotemporal dimension of both animal tracking data sets and the dynamic environmental data that can be associated with them. Typically, these geographic layers derive from remote sensing measurements, commonly those collected by sensors deployed on earth-orbiting satellites, which can be updated on a monthly, weekly or even daily basis. The modelling potential for integrating these two levels of ecological complexity (animal movement and environmental variability) is huge and comes from the possibility to investigate processes as they build up, i.e. in a full dynamic framework. This chapter’s exercise will describe how to integrate dynamic environmental data in the spatial database and join to animal locations one of the most used indices for ecological productivity and phenology, the normalised difference vegetation index (NDVI) derived from MODIS. The exercise is based on the database built so far in Chaps. 2, 3, 4, 5 and 6.

A Step Further in the Integration of Data Management and Analysis: Pl/R

This chapter introduces the Pl/R extension, a very powerful alternative to integrate the features offered by R in the database in a gapless workflow. Pl/R is a loadable procedural language that allows the use of the R engine and libraries directly inside the database, thus embedding R scripts into SQL statements and database functions and triggers. Among many advantages, Pl/R avoids unnecessary data replication, allows the use of a single SQL interface for complex scripts involving R queries and offers a tight integration of data analysis and management processes into the database. In this chapter, you will have a basic overview of the potential of Pl/R for the study of GPS locations. You will be introduced to the use of Pl/R, starting with exercises involving simple calculations in R (logarithms, median and quantiles), followed by more elaborated exercises designed to compute the daylight times of a given location at a given date, or to compute complex home range methods.