Lise M. Aubry

Early development, recruitment and life history trajectory in long-lived birds

Lindström (in Trends Ecol Evol 14:343–347, 1999) synthesized knowledge about “early development and fitness in birds and mammals”, interesting tracks and challenges for future studies. Today, there is unambiguous evidence that Lindström’s first statement holds in long-lived birds: “It is obvious that adverse environmental conditions might have immediate effects […].” However, whether there are “long-term fitness consequences of conditions experienced during early development” (Lindström’s second statement) is unclear for long-lived birds. The extent to which the disadvantage of frail individuals at independence is expressed predominantly in terms of higher mortality and disappearance from the population before recruitment, or persists after recruitment, is still an open question. Due to the rarity of relevant data and the fact that most studies are retrospective, heterogeneity in methods and timescales hampers the identification of general patterns. Nevertheless, several studies have provided evidence of a relationship between early conditions and future reproductive parameters, or lifetime reproductive success. Evidence from large mammals suggests substantial long-term individual and population effects of early conditions, including trans-generational maternal effects. Evidence from short-lived birds also suggests long-term individual consequences, and maternal effects have been documented in long-lived ones. Despite logistical and financial difficulties inherent in long-term studies, they are the only way of addressing Lindström’s second statement. Existing long-term longitudinal datasets should be re-analyzed using recently developed capture–mark–recapture models handling state uncertainty and unobservable heterogeneity in populations. Statistical methods designed to estimate lifetime reproductive success or incorporate pedigree information in standard situations of studies of wild vertebrates with imperfect detection offer new opportunities to assess long-term fitness consequences of early development in long-lived birds.

Methods for studying cause‐specific senescence in the wild

Summary 1. The founding evolutionary theories of ageing indicate that the force of mortality imposed by environmental factors should influence the strength of natural selection against actuarial senescence and its evolution. To rigorously test this idea, field biologists need methods that yield estimates of age-specific mortality according to cause of death. 2. Here, we present existing methods commonly applied in studies of human health that could be used to accomplish these goals in studies of wild species for which fate can be determined with certainty. We further present a new application of hidden Markov models for capture-reencounter studies of wild animals that can be used to estimate age-specific trajectories of cause-specific mortality when detection is imperfect. 3. By applying our new hidden Markov model with the E-SURGE and MARK softwares to capture-reencounter data sets for long-lived species, we demonstrate that senescence can be severe for natural causes of mortality in the wild, while being largely non-existent for anthropogenic causes. 4. Moreover, we show that conflation of mortality causes in commonly used survival analyses can induce an underestimation of the intensity of senescence and overestimation of mortality for pre-senescent adults. These biases have important implications for both age-structured population modelling used to guide conservation and comparative analyses of senescence across species. Similar to frailty, individual differences in causes of death can generate individual heterogeneity that needs to be accounted for when estimating age-specific mortality patterns. 5. The proposed hidden Markov method and other competing risk estimators can nevertheless be used to formally account for these confounding effects, and we additionally discuss how our new method can be used to gain insight into the mechanisms that drive variation in ageing across the tree of life.

Wolf in sheep’s clothing: Model misspecification undermines tests of the neutral theory for life histories

Abstract Understanding the processes behind change in reproductive state along life‐history trajectories is a salient research program in evolutionary ecology. Two processes, state dependence and heterogeneity, can drive the dynamics of change among states. Both processes can operate simultaneously, begging the difficult question of how to tease them apart in practice. The Neutral Theory for Life Histories (NTLH) holds that the bulk of variations in life‐history trajectories is due to state dependence and is hence neutral: Once previous (breeding) state is taken into account, variations are mostly random. Lifetime reproductive success (LRS), the number of descendants produced over an individuals reproductive life span, has been used to infer support for NTLH in natura. Support stemmed from accurate prediction of the population‐level distribution of LRS with parameters estimated from a state dependence model. We show with Monte Carlo simulations that the current reliance of NTLH on LRS prediction in a null hypothesis framework easily leads to selecting a misspecified model, biased estimates and flawed inferences. Support for the NTLH can be spurious because of a systematic positive bias in estimated state dependence when heterogeneity is present in the data but ignored in the analysis. This bias can lead to spurious positive covariance between fitness components when there is in fact an underlying trade‐off. Furthermore, neutrality implied by NTLH needs a clarification because of a probable disjunction between its common understanding by evolutionary ecologists and its translation into statistical models of life‐history trajectories. Irrespective of what neutrality entails, testing hypotheses about the dynamics of change among states in life histories requires a multimodel framework because state dependence and heterogeneity can easily be mistaken for each other.

The Influence of Snowmobile Trails on Coyote Movements during Winter in High-Elevation Landscapes

Competition between sympatric carnivores has long been of interest to ecologists. Increased understanding of these interactions can be useful for conservation planning. Increased snowmobile traffic on public lands and in habitats used by Canada lynx (Lynx canadensis) remains controversial due to the concern of coyote (Canis latrans) use of snowmobile trails and potential competition with lynx. Determining the variables influencing coyote use of snowmobile trails has been a priority for managers attempting to conserve lynx and their critical habitat. During 2 winters in northwest Wyoming, we backtracked coyotes for 265 km to determine how varying snow characteristics influenced coyote movements; 278 km of random backtracking was conducted simultaneously for comparison. Despite deep snow (>1 m deep), radio-collared coyotes persisted at high elevations (>2,500 m) year-round. All coyotes used snowmobile trails for some portion of their travel. Coyotes used snowmobile trails for 35% of their travel distance (random: 13%) for a mean distance of 149 m (random: 59 m). Coyote use of snowmobile trails increased as snow depth and penetrability off trails increased. Essentially, snow characteristics were most influential on how much time coyotes spent on snowmobile trails. In the early months of winter, snow depth was low, yet the snow column remained dry and the coyotes traveled off trails. As winter progressed and snow depth increased and snow penetrability increased, coyotes spent more travel distance on snowmobile trails. As spring approached, the snow depth remained high but penetrability decreased, hence coyotes traveled less on snowmobile trails because the snow column off trail was more supportive. Additionally, coyotes traveled closer to snowmobile trails than randomly expected and selected shallower snow when traveling off trails. Coyotes also preferred using snowmobile trails to access ungulate kills. Snow compaction from winter recreation influenced coyote movements within an area containing lynx and designated lynx habitat.