Abstract Tipping point theory has garnered substantial attention over recent decades. It predicts abrupt and often irreversible transitions from one ecosystem state to an alternative state. However, ecosystem models that predict tipping typically neglect spatial dynamics. Recent studies reveal that incorporating spatial dynamics may enable ecosystems to evade tipping predicted by nonspatial models. Here, we use a dryland and a savanna-forest model to synthesize mechanisms by which spatial processes can alter the theory of tipping. We further propose that the underlying drivers of positive feedback leading to alternative stable states may provide insight into the tipping evasion mechanisms most relevant to a specific ecosystem. For instance, while positive feedbacks may arise in drylands from direct self-facilitation, such as enhancing the uptake of a limiting resource, at the savanna-forest boundary, it may arise from mutual inhibition between two ecosystem components. In the former case ecosystems can evade tipping by forming self-organized patterns, whereas in the latter the presence of environmental heterogeneity may be required. Our study highlights that deepening our understanding of how ecological feedbacks connect to tipping evasion mechanisms is crucial to formulate better strategies to increase ecosystem resilience.

Abstract Life has evolved different strategies to take advantage of seasonal changes in the environment that are emblematic of boreal and arctic biomes. However, ecological theories often ignore seasonal changes for tractability or simplicity. Understanding the effect of seasonality may prove crucial as the changing climate puts more pressure on ecosystems. Hybrid dynamical models are an efficient way to represent seasonal adaptations where switches in food web compositions account for species migrations and predator movements. We use the highly seasonal and cyclic dynamics of an Arctic food web to showcase the utility of hybrid models. The simplified representation of community dynamics provided by the hybrid framework eases the study of conditions leading to lemming cycles and facilitates parameterization with empirical data. We corroborate that seasonal switches, accounting for the onset of reproduction of resident predators and the migration of mobile predators, likely drive cyclic fluctuations in lemming abundance. Our empirical investigation reveals that each predator alone does not reduce lemming growth rate enough to generate population cycles, which reinforces the idea that the predator community as a whole is responsible for the cyclic dynamics. This situation arises because each predator has unique adaptations to seasonality and impacts the dynamics in different but complementary ways. Our results have implications for community ecology, as they show how hybrid models can help understand complex dynamics in highly seasonal ecosystems. This is especially relevant in the Arctic, considering that rapid warming has the potential to disrupt lemming population cycles and negatively affect their predators.

Abstract Navigation to and from a familiar site is a common animal behavior called homing. Many species use olfactory environmental landmarks or scents deposited in the environment by themselves or their conspecifics for homing. Birds regularly commute to and from their nest, and olfaction, an underappreciated sense in birds, may facilitate this behavior. Burrow-nesting seabirds, for example, rely on olfaction to locate their breeding colony and to identify their burrow, but the specific chemical information they use is unclear. We examined the chemical profiles of the colony landscape and its avian occupants at a breeding island of Leach's storm petrels (Hydrobates leucorhous) to determine whether place-specific chemicals, bird-produced chemicals, or both enable homeward navigation in this burrow-nesting species. We found that the colony contains spatial gradients of chemicals that may facilitate multiple stages of homing. We also show that burrows possess unique odors owing to chemicals deposited by their occupants. Moreover, the burrow shapes the odor of the birds such that individuals carry the scent of their nest and mated pairs possess similar chemical profiles. The bidirectional transfer of compounds between burrows and birds may enable burrow recognition in this species and potentially functions as a means of communication between conspecifics.

Abstract Milk is not cheap. The energetic cost for mammalian mothers to provide and sustain milk production makes it a finite resource. Offspring are therefore expected to wean before sexual maturity and reproductive activity, whether on their own or through termination by their mothers. Weaning delays should result in a reproductive trade-off for the mother: the possibility of begetting a fitter pup at the cost of a longer interbirth interval. Using 20 years of data, we show the occurrence of repeated suckling events between female Galápagos sea lions (GSLs; Zalophus wollebaeki) and their adult (≥5 years) biological offspring well beyond the average age of independence and when the offspring are themselves already reproductively active. This behavior, "supersuckling," suggests that GSL mother-offspring relationships are more complex and longer lasting than previously thought. To our knowledge, this is the first long-term documentation of known mother-offspring pairs repeatedly performing this behavior in any marine mammal species.

Abstract Pollinators are important drivers of floral variation and speciation in plants. Here we investigate the effects of functional trait matching on pollen receipt in two plant species, Tritoniopsis revoluta and Nerine humilis, each visited by long-proboscid nemestrinid flies and bees across their ranges. Using single visits by pollinators to flowers with increased variance in floral morphology, we construct performance surfaces based on pollen receipt. We find divergent pollen receipt surfaces mediated by functionally different pollinators, within and between plant populations. Our results illuminate the nuances of how plants adapt to increase reproductive output in multipollinator communities, in which pollinators vary in their effectiveness.

Abstract Evaluating the evolutionary impacts of anthropogenic activity on populations is key to understanding species resiliency and to designing effective conservation strategies. Sequencing DNA from historical specimens provides the opportunity to establish a historical baseline and empirically assess changes in genetic diversity, changes in effective population size, and selection over time. Here, we sequenced historical and contemporary samples of the cardinalfish Taeniamia zosterophora collected in 1908 and in 2021-2022 across two sites with differing human impact in the Philippines. At both sites, genetic diversity increased over time, with contemporary samples having significantly higher Watterson's θ than historical samples. This diversity increase was primarily attributable to positive selection on low-frequency alleles such that they increased toward intermediate frequencies through time. For the putatively neutral fraction of the genome, in contrast, there was a slight but significant decline in Watterson's θ at both low and high human impact sites, suggesting that drift strengthened and effective population sizes declined through time. There was more evidence for selection and greater loss of neutral diversity at the site with higher human impact. Our results provide empirical evidence for the surprising preservation of genetic diversity through the action of natural selection in the face of anthropogenic impacts.