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Understanding how conditions experienced during development affect reproductive timing is of considerable cross-disciplinary interest. Life-history theory predicts that organisms will accelerate reproduction when future survival is unsure. In humans, this can be triggered by early exposure to mortality. Previous studies, however, have been inconclusive due to several confounds that are also likely to affect reproduction. Here we take advantage of a natural experiment in which a population is temporarily divided by war to analyze how exposure to mortality affects reproduction. Using records of Finnish women in World War II, we find that young girls serving in a paramilitary organization wait less time to reproduce, have shorter inter-birth intervals, and have more children than their non-serving peers or sisters. These results support the hypothesis that exposure to elevated mortality rates during development can result in accelerated reproductive schedules and adds to our understanding of how participation in warfare affects women. Life history theory predicts that females will adjust reproductive timing in response to environmental challenges. Here the authors show that young girls exposed to higher mortality rates during war give birth earlier and more often than their peers who were not exposed to these conditions.

Organisms colonizing new habitats can undergo adaptive change due to novel selective landscapes encountered in the new environment. Examples in nature where the development of the same traits has repeatedly occurred on multiple independent occasions upon colonizing a novel habitat represent instances of parallel evolution. Here we test whether the colonization of spring habitat by the principally lacustrine amphipod crustacean Pallaseopsis quadrispinosa has resulted in parallel evolution in armature traits using empirical data on morphology and mitochondrial DNA and through a breeding experiment. Analysis of mtDNA CO1 sequences shows that the spring populations share no common history and have evolved in isolation from each other and from their neighbouring lake populations since deglaciation approximately 12,000 years ago and are now fixed for different haplogroups. Dorsal spines and lateral projections were absent or less developed in all spring populations than in lake populations. Variation in armature development also could be explained by predator presence as populations with fish predators exhibited more developed spines than those without fish. In a laboratory breeding experiment, hybrid Spring × Lake F1 offspring had intermediate development of armature compared to offspring of Lake × Lake and Spring × Spring matings. The results support the hypothesis that armature reduction has independently evolved on multiple occasions in P. quadrispinosa. Recent research has questioned the degree to which parallel evolution actually explains variance in traits. Taking into account the predation regime, sexual dimorphism and mineral composition of the trait, a more precise understanding of the factors influencing parallel evolution emerges. Using evidence from field sampling and laboratory experimentation, we describe how habitat differences and the presence or absence of fish predators influence spine morphology in an amphipod crustacean. Overall, such a clear and revealing demonstration of selection on an antipredator trait in a natural setting has great value for the understanding of the role of selection by predation on morphological evolution.

We studied a previously almost unknown nocturnal mammal, an apparently undescribed species of tree hyrax ( Dendrohyrax sp.) in the moist montane forests of Taita Hills, Kenya. We used thermal imaging to locate tree hyraxes, observe their behavior, and to identify woody plants most frequently visited by the selective browsers. We also documented acoustic behavior in forest fragments of different sizes. Data on calling type and frequency were analyzed together with lidar data to estimate population densities and to identify forest stand characteristics associated with large populations. Viable populations were found only in the largest forest fragments (> 90 ha), where tree hyraxes preferred most pristine forest stands with high, multilayered canopies. The estimated population sizes in smaller forest fragments were very limited, and hyraxes were heard to call only during late night and early morning hours, presumably in order to avoid detection. While we frequently recorded tree hyrax songs in the largest forest fragments, we almost never heard songs in the small ones. All remaining subpopulations of the Taita tree hyrax are under threat of human disturbance and further habitat deterioration. Conservation efforts should include protection of all remaining habitat patches, but also reforestation of former habitat is urgently needed.

Age and size at maturation are important correlates of fitness in many organisms and understanding how these are influenced by environmental conditions is therefore required to predict populations' responses to environmental changes. In ectotherms, growth and maturation are closely linked to temperature, but nonetheless it is often unclear how temperature-induced variation in growth and temperature per se translate to the process of maturation. Here, we test this explicitly with a common garden experiment using ninespined sticklebacks (Pungitius pungitius). We reared fish in 14 and 17°C and recorded high resolution growth trajectories and the timing of maturation on an individual basis. To characterize the growth of each individual, we fitted a von Bertalanffy growth curve to each measured growth trajectory, so that the three parameters of the curve provided a summary of an individual's growth. Temperature treatments induced changes in both the growth parameters and the age at maturation. In females, changes in the age of maturation were encompassed by variations in growth, whereas in males there was a temperature-related shift in the age at maturation that was unrelated to growth. Our experiment demonstrates that temperature can affect maturation directly, and not only through temperature-induced changes in growth. Therefore, one cannot predict, on the basis of growth only, how changes in temperature might alter age and size at maturation and the subsequent reproduction.

Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1ω7 and partly 18:1ω9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, α-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain ω-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.

Dispersal does not only mean moving from one environment to another, but can also refer to shifting from one social group to another. Individual characteristics such as sex, age and family structure might influence an individual's propensity to disperse. In this study, we use a unique dataset of an evacuated World War II Finnish population, to test how sex, age, number of siblings and birth order influence an individual's dispersal away from their own social group at a time when society was rapidly changing. We found that young women dispersed more than young men, but the difference decreased with age. This suggests that young men might benefit more from staying near a familiar social group, whereas young women could benefit more from moving elsewhere to find work or spouses. We also found that having more younger brothers increased the propensity for firstborns to disperse more than for laterborns, indicating that younger brothers might pressure firstborn individuals into leaving. However, sisters did not have the same effect as brothers. Overall, the results show that individual characteristics are important in understanding dispersal behaviour, but environmental properties such as social structure and the period of flux after World War II might upend the standard predictions concerning residence and dispersal. Social media summary: Individual characteristics influence dispersal away from social group after a forced migration in a Finnish population

The estimation of individual fitness and quality are important elements of evolutionary ecological research. Over the past six decades, there has been great interest in using fluctuating asymmetry (FA) to represent individual quality, yet, serious technical problems have hampered efforts to estimate the heritability of FA, which, in turn, has limited progress in the investigation of FA from an evolutionary perspective. Here we estimate the heritability of number of lateral plates, their FA and directional asymmetry (DA) in threespine stickleback, Gasterosteus aculeatus. By (i) using a meristic trait and (ii) basing our calculations on a large half-sib design experiment involving 2,079 offspring from 84 families, we overcame many of the difficulties faced by earlier FA studies. Both lateral plate number and FA in lateral plates were heritable (h(2) = 0.46 and 0.21, respectively), even after controlling for marker genotypes linked to EDA (the major locus influencing plate number). Likewise, DA in lateral plates was heritable h(2) = 0.23). The additive genetic component of FA in lateral plates makes it a prime candidate for further investigation into the evolutionary implications of FA and the genetic underpinnings of developmental instability. This discovery in an evolutionary model species holds the possibility to invigorate the study of FA from an evolutionary perspective.

Improving public engagement in ecological research improves the visibility of science and educates a wider audience about the value of ecology and its study. To this end, we assess the success of two simple activities, designed to track forest cover and understorey conditions, implemented at Lammi Biological Station Science Trail, Finland, in terms of effective public participation and useability of the data generated. We consider how best to engage participants in the activities, and we validate the data obtained by comparison of its reliability and useability against standard ecological approaches. It is also increasingly timely for researchers to utilise the large datasets that can be generated through effective public engagement. If experiments are effectively designed, these data can provide information at a larger scale than is attainable with the resources typically available to individual research projects. Consequently, given high enough uptake, such activities hold the potential for upscaling or generalisation from their findings. Both activities proved useful to collect more intensive data than would otherwise have been feasible. The quadrat vegetation survey (Activity 1) provided useable data to determine species phenology but not species composition. The canopy disk observations (Activity 2) reliably tracked seasonal changes in canopy cover when calibrated against baseline data. Training in these activities fostered engagement in how climate change affects forest ecology, improving the quality of data collected, and engaging participants eager to learn about and contribute to research into these processes.

In conservation, the use of unmanned aerial vehicles (drones) carrying various sensors and the use of deep learning are increasing, but they are typically used independently of each other. Untapping their large potential requires integrating these tools. We combine drone-borne thermal imaging with artificial intelligence to locate ground-nests of birds on agricultural land. We show, for the first time, that this semi-automated system can identify nests with a high performance. However, local weather, type of arable field and height of the drone can affect performance. The results’ implications are particularly relevant to conservation practitioners working across sectors, such as biodiversity conservation and food production in farmland. Under a rapidly changing world, studies like this can help uncover the potential of technology for conservation and embrace cross-sectoral transformations from the onset; for example, by integrating nest detection within the precision agriculture system that heavily relies on drone-borne sensors.

The spatial ecology of stalk‐and‐ambush predators like the Eurasian lynx Lynx lynx depends on prey availability and environmental features, yet the relative roles of these factors remain unclear at large spatial scales. In this study, we analysed lynx habitat use across central and southern Finland using snow‐track data from the Wildlife Triangle Scheme (2016–2020) and a joint species distribution modelling framework (HMSC) to assess both environmental drivers and spatial predator–prey associations. The Finnish lynx population offers a unique opportunity to study a contiguous population with stark regional differences in prey availability, enabling inferences about environmental and prey effects on space use. Across the study area, lynx habitat use was primarily associated with structurally complex forests and terrain, as expected for a stalk‑and‑ambush predator. Overall, environmental conditions explained habitat use patterns to a greater degree in the central region than in the south, which we posit is due to differences between the regions in prey species. In the central region, habitat use by lynx and its prey, the mountain hare Lepus timidus, was similar, in contrast to the southern region, where lynx were spatially associated with roe deer Capreolus capreolus and white‐tailed deer Odocoileus virginianus, both of which showed habitat use patterns differing from those of lynx. These results indicate that lynx adjust their space use according to prey availability, while still retaining a core preference for complex habitat, as expected for a stalk‐and‐ambush predator. Our results are a clear demonstration of how the interplay between environmental conditions and community composition of prey shapes a generalist predator's habitat use and how this can contribute to overall resilience at the population level. Our study captures insights into habitat use at the landscape scale across contrasting ecological contexts, with implications for the management and conservation of large carnivores in human‐modified environments.