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Pathways to extinction start long before the death of the last individual. However, causes of early stage population declines and the susceptibility of small residual populations to extirpation are typically studied in isolation. Using validated process-explicit models, we disentangle the ecological mechanisms and threats that were integral in the initial decline and later extinction of the woolly mammoth. We show that reconciling ancient DNA data on woolly mammoth population decline with fossil evidence of location and timing of extinction requires process-explicit models with specific demographic and niche constraints, and a constrained synergy of climatic change and human impacts. Validated models needed humans to hasten climate-driven population declines by many millennia, and to allow woolly mammoths to persist in mainland Arctic refugia until the mid-Holocene. Our results show that the role of humans in the extinction dynamics of woolly mammoth began well before the Holocene, exerting lasting effects on the spatial pattern and timing of its range-wide extinction.

Pathways to extinction start long before the death of the last individual. However, causes of early-stage population declines and the susceptibility of small residual populations to extirpation are typically studied in isolation. Using validated process-explicit models, we disentangle the ecological mechanisms and threats that were integral in the initial decline and later extinction of the woolly mammoth. We show that reconciling ancient DNA data on woolly mammoth population decline with fossil evidence of location and timing of extinction requires process-explicit models with specific demographic and niche constraints, and a constrained synergy of climatic change and human impacts. Validated models needed humans to hasten climate-driven population declines by many millennia, and to allow woolly mammoths to persist in mainland Arctic refugia until the mid-Holocene. Our results show that the role of humans in the extinction dynamics of woolly mammoth began well before the Holocene, exerting lasting effects on the spatial pattern and timing of its range-wide extinction.

Using the past to inform the future The late Quaternary paleorecord, within the past ∼130,000 years, can help to inform present-day management of the Earth's ecosystems and biota under climate change. Fordham et al. review when and where rapid climate transitions can be found in the paleoclimate record. They show how such events in Earth's history can shape our understanding of the consequences of future global warming, including rates of biodiversity loss, changes in ecosystem structure and function, and degradation in the goods and services that these ecosystems provide to humanity. They also highlight how recent developments at the intersection of paleoecology, paleoclimatology, and macroecology can provide opportunities to anticipate and manage the responses of species and ecosystems to changing climates in the Anthropocene. Science , this issue p. eabc5654

Two major challenges in studying the impacts of exotic invasive species on native species are identifying mechanisms of displacement and replacement and the lack of long-term population studies in these systems. A solution for the first is to study invasive and native congeners that occupy the same niche. A solution for the second is to study many populations for one year instead of one population for many years. We studied the invasion biology of the invasive European paper wasp Polistes dominula and its native congener the Northern paper wasp P. fuscatus, two species which compete for similar resources. We tracked the demography of the two wasps at sites in the northeastern United States. We found that the survival of P. dominula to the reproductive period in August was three times that of P. fuscatus, across all sites. The reproductive output of P. fuscatus declined in direct proportion to the percentage of P. dominula nests at the site. P. fuscatus nests at uninvaded sites had three times the nest cells of those at the most invaded sites. These findings suggest a positive feedback cycle in the establishment of P. dominula, in which the invasive wasp drives population declines in the native that in turn allow P. dominula to further establish. This system provides an example of a possible extinction vortex caused by competitive exclusion of a species by its invasive congener.

Population dynamics are typically temporally autocorrelated: population sizes are positively or negatively correlated with past population sizes. Previous studies have found that positive temporal autocorrelation increases the risk of extinction due to ‘inertia’ that prolongs downward fluctuations in population size. However, temporal autocorrelation has not yet been analyzed at the level of life cycle transitions. We developed an R package, colorednoise, which creates stochastic matrix population projections with distinct temporal autocorrelation values for each matrix element. We used it to analyze long-term demographic data on 25 populations from the COMADRE and COMPADRE databases and simulate their stochastic dynamics. We found a broad range of temporal autocorrelation across species, populations and life cycle stages. The number of stage-classes in the matrix strongly affected the temporal autocorrelation of the growth rate. In the plant populations, reproduction transitions had more negative temporal autocorrelation than survival transitions, and matrices dominated by positive temporal autocorrelation had higher extinction risk, while in animal populations transition type was not associated with noise color. Our results indicate that temporal autocorrelation varies across life cycle transitions, even among populations of the same species. We present the colorednoise package for researchers to analyze the temporal autocorrelation of structured demographic rates.

The haploid susceptibility hypothesis (HSH) was proposed as an explanation for how behavioral roles in haplodiploid social systems evolved. It posits that haploid males are more susceptible to disease than diploid females due to decreased genetic variability at key disease resistance loci. The resulting decreased immunocompetence is hypothesized to have played a role in the evolution of social behavior by limiting the behavioral repertoire haploids perform. Here, we test this hypothesis in a study system that separates ploidy from behavioral sex roles: Polistes dominulus, a social wasp, has colonies with naturally occurring diploid males. We report results from two immune function assays—hemolymph phenoloxidase activity and encapsulation response—performed on haploid males, diploid males, and diploid females. Our data suggest that ploidy is not a significant contributor to immune function in P. dominulus; thus, our data do not support the HSH for the evolution of behavioral roles. Instead, our data indicate that time of emergence is the best predictor of immune function in Polistes. We speculate that seasonal trends result from seasonal differences in pathogens and parasites.

Elaborate male traits are typically used to attract mates and to compete with other males for mating opportunities. However, similarly ornate secondary sexual characteristics are also found in females in many species and may be used in competition in both sexual and nonsexual contexts. Trait elaboration in females may be particularly important in cooperatively breeding species where reproduction is monopolized by a few individuals in a group and where both sexes must compete for these limited mating opportunities. Previous work in African starlings has shown that females in cooperatively breeding species are larger and more ornamented than those in noncooperative species, resulting in reduced plumage and size dimorphism. To further examine patterns of sexual dimorphism in signalling traits and to better understand their role in mediating social competition, we investigated the form and function of song in cooperatively breeding superb starlings, Lamprotornis superbus. In addition to comparing song between sexes, we contrasted song in dominant breeders and subordinate helpers of both sexes and examined its use in various social contexts. We found that song was indistinguishable between males and females, with both sexes showing similar complexity, pitch, versatility and structure. However, the song of breeders was more versatile than that of helpers. Moreover, song structure differed when birds sang in chorus from when they sang alone. These findings suggest that, like male song, female song may be used in social competition, and that song may be an important signal in both sexes in species