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Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.

Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size-fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.

Indirect climate effects on tree fecundity that come through variation in size and growth (climate-condition interactions) are not currently part of models used to predict future forests. Trends in species abundances predicted from meta-analyses and species distribution models will be misleading if they depend on the conditions of individuals. Here we find from a synthesis of tree species in North America that climate-condition interactions dominate responses through two pathways, i) effects of growth that depend on climate, and ii) effects of climate that depend on tree size. Because tree fecundity first increases and then declines with size, climate change that stimulates growth promotes a shift of small trees to more fecund sizes, but the opposite can be true for large sizes. Change the depresses growth also affects fecundity. We find a biogeographic divide, with these interactions reducing fecundity in the West and increasing it in the East. Continental-scale responses of these forests are thus driven largely by indirect effects, recommending management for climate change that considers multiple demographic rates.

The drivers of year-to-year difference in winter abundance patterns, particularly dramatic in the 'eruptions' of many boreal seed-eating birds, are poorly understood. Varied Thrush (Ixoreus naevius (Gmelin, 1789)), endemic to the Pacific Northwest of North America, is a boreal species that exhibits pronounced, often biennially cyclic, changes in winter abundance within most of its normal wintering range. Although the drivers of this variability have not previously been explored, it has been suggested that differences in acorn abundance, a key winter food resource, might be important. Here, we examine three hypotheses for the drivers of this pattern: the acorn crop within the bird's normal winter range, weather within the bird's winter range, and weather during the previous breeding season within the bird's breeding range. Analyses supported the importance of breeding season conditions, particularly breeding season rainfall, with more birds wintering following wetter years. No support was found for the hypotheses that winter conditions, neither the acorn crop nor winter weather, correlate with winter abundance patterns. For this forest species, year-to-year differences in winter abundance patterns are apparently not driven by the 'pull' of winter food supply or winter conditions, but by environmental factors during the prior breeding season that presumably affect reproductive success and subsequent population size. Key words: acorn crop, Ixoreus naevius, population eruptions, population variability, Varied Thrush Les facteurs à l'origine des variations interannuelles des motifs d'abondance hivernale, dont les [beaucoup moins que] éruptions [beaucoup plus grand que] de nombreux oiseaux granivores boréaux constituent des exemples particulièrement frappants, ne sont pas bien compris. La grive à collier (Ixoreus naevius (Gmelin, 1789)), endémique à la région de la côte nord-ouest du Pacifique d'Amérique du Nord, est une espèce boréale qui présente des variations prononcées, suivant souvent un cycle de deux ans, d'abondance hivernale dans la majeure partie de son aire d'hivernage normale. Bien que les facteurs à l'origine de cette variabilité n'aient pas été explorés par le passé, il a été proposé que des variations de l'abondance de glands, une ressource alimentaire hivernale clé, pourraient être importantes. Nous examinons trois facteurs qui pourraient être à l'origine de ce motif, à savoir : la production de glands dans l'aire d'hivernage normale de l'oiseau, la météo dans l'aire d'hivernage de l'oiseau et la météo durant la saison de reproduction précédente dans l'aire de reproduction de l'oiseau. Des analyses appuient l'importance des conditions durant la saison de reproduction, en particulier la pluviométrie, un plus grand nombre d'oiseaux hivernant après des années plus humides. Aucun résultat n'appuie les hypothèses voulant que les conditions hivernales, qu'il s'agisse de la production de glands ou de la météo hivernale, soient corrélées aux motifs d'abondance hivernale. Pour cette espèce forestière, les variations interannuelles des motifs d'abondance hivernale ne semblent pas mues par l'attrait de ressources alimentaires hivernales ni pas les conditions hivernales, mais plutôt par des facteurs environnementaux durant la saison de reproduction précédente, qui ont présumément un effet sur le succès de reproduction et la taille subséquente de la population. [Traduit par la Rédaction] Mots-clés : production de glands, Ixoreus naevius, éruptions démographiques, variabilité démographique, grive à collier, Introduction Dramatic year-to-year variability in wintering abundance and distribution patterns, particularly among boreal seed-eating birds, has often been associated with cycles in food availability (Lack 1954; Bock and Lepthien 1976; [...]

Mast seeding, the synchronous and highly variable production of seed crops by perennial plants, is a population‐level phenomenon and has cascading effects in ecosystems. Mast seeding studies are typically conducted at the population/species level. Much less is known about synchrony in mast seeding between species because the necessary long‐term data are rarely available. To investigate synchrony between species within communities, we used long‐term data from seven forest communities in the U.S. Long‐Term Ecological Research (LTER) network, ranging from tropical rainforest to boreal forest. We focus on cross‐species synchrony and (i) quantify synchrony in reproduction overall and within LTER sites, (ii) test for relationships between synchrony with trait and phylogenetic similarity and (iii) investigate how climate conditions at sites are related to levels of synchrony. Overall, reproductive synchrony between woody plant species was greater than expected by chance, but spanned a wide range of values between species. Based on 11 functional and reproductive traits for 103 species (plus phylogenetic relatedness), cross‐species synchrony in reproduction was driven primarily by trait similarity with phylogeny being largely unimportant, and synchrony was higher in sites with greater climatic water deficit. Community‐level synchrony in masting has consequences for understanding forest regeneration dynamics and consumer‐resource interactions. [ABSTRACT FROM AUTHOR]

:   Avian trichomonosis, a disease typically caused by the protozoan parasite Trichomonas gallinae , is a well recognized cause of death in many avian species. In California, US, trichomonosis has caused periodic epidemics in Pacific Coast Band-tailed Pigeons ( Patagioenas fasciata monilis). We summarize reported mortality events and investigate ecologic drivers and population impacts associated with epidemic mortality due to trichomonosis in Band-tailed Pigeons. Between 1945 and 2014, 59 mortality events involving Band-tailed Pigeons were reported in California with the number of reported events increasing over time. Estimated mortality for these events was variable, ranging between 10 and 10,000 pigeons. Events were most-frequently reported in Monterey (19%; 11/59) and San Luis Obispo (8%; 5/59) counties. Events often started in January (32%; 9/28) and February (50%; 14/28) and lasted 5-68 d. Impacts of mortality events on pigeon populations were indicated by Breeding Bird Survey and Christmas Bird Count abundance indices, which showed a decline in outbreak years compared to nonoutbreak years. Environmental conditions most associated with outbreak years included higher average temperatures between January and March, the period most associated with mortality events, and lower average precipitation in December just prior to mortality events. In Monterey County, events tended to occur in winters following higher acorn production of coast live oaks ( Quercus agrifolia ) in the fall. Weather and food abundance could be related to increased transmission or enhanced viability of Trichomonas spp. Although estimated mortality due to avian trichomonosis was highly variable across years, cumulative losses were substantial and likely to have a negative impact on population size.

Masting behavior--variable and synchronized reproduction by a population of plants--has long been recognized as correlating with weather. How and why weather conditions influence seed production is, however, poorly understood. We investigated the relationships between acorn production and both local weather and long-term climate in 10 populations across the geographic range of the valley oak (Quercus lobata Nee), a California endemic that matures acorns in a single season. Acorn production was larger following a cold spring in the prior year and dry conditions in the winter and spring immediately preceding acorn maturation; similar patterns were also found, with minor differences, at all 10 individual sites. The strength of the relationships varied geographically in the case of the correlation between winter rainfall and annual acorn production, which was stronger (more negative) at wetter sites. Thus, in contrast to a recent study in Quercus petraea (Matt.) Liebl., weather had generally similar effects on acorn production throughout the range of Q. lobata. Similar to Q. petraea, however, the strength of the relationship between site-level annual acorn production and one of the weather factors affecting acorn production (winter rainfall in the case of Q. lobata) varied geographically in ways that may be related to differences among sites in the degree of pollen limitation. Understanding the mechanisms by which weather affects seed production is challenging but critical if we are to understand how climate change will affect masting behavior in the future. Key words: acorn production, masting, Quercus lobata, valley oak, variable reproduction. Il est depuis longtemps reconnu que la reproduction synchronisee et variable dans une population de plantes (<>) est correlee avec les conditions meteorologiques. Cependant, on comprend mal comment et pourquoi les conditions meteorologiques influencent la production de semences. Nous avons etudie les relations entre la production de glands et les conditions meteorologiques locales ainsi que le climat a long terme chez 10 populations dans l'aire de repartition du chene lobe (Quercus lobata Nee), un chene endemique de la Californie dont les glands arrivent a maturite en une seule saison. La production de gland etait plus abondante a la suite d'un printemps froid l'annee precedente et des conditions seches durant l'hiver et le printemps precedant immediatement la maturation des glands. Des patrons similaires ont ete observes, avec des differences mineures, dans l'ensemble des 10 stations individuelles. La force de la relation variait geographiquement dans le cas de la correlation entre la chute de pluie hivernale et la production annuelle de glands; la correlation etait plus forte (plus negative) dans les stations plus humides. Par consequent, contrairement a une etude recente qui portait sur Quercus petraea (Matt.) Liebl., les conditions meteorologiques avaient generalement des effets similaires sur la production de glands partout dans l'aire de repartition de Q. lobata. Comme avec Q. petraea cependant, la force de la relation entre la production annuelle de glands a l'echelle de la station et un des facteurs meteorologiques qui influencent la production de glands (chute de pluie hivernale dans le cas de Q. lobata) variait d'un endroit a l'autre. Cette variation pouvait etre reliee a des differences entre les stations concernant la disponibilite du pollen. Il est difficile mais essentiel de comprendre les mecanismes par lesquels les conditions meteorologiques influencent la production de semences si nous voulons comprendre de quelle facon le changement climatique affectera la reproduction synchronisee dans le futur. [Traduit par la Redaction] Mots-cles: production de glands, masting, Quercus lobata, vallee du chene, reproduction variable., Introduction Variable, synchronized seed production, known as mast-fruiting or masting behavior, is commonly observed in many taxa of plants and is particularly widespread among temperate and boreal trees. The evolutionary [...]

In cooperatively breeding acorn woodpeckers (Melanerpes formicivorus), helper males have a large positive effect on fledging success in good acorn crop years but only a small positive effect in poor acorn crop years, while helper females exhibit the opposite pattern. Based on these findings, we tested the “concealed helper effects” hypothesis, which proposes that laying females reduce investment in eggs (with respect to their size, number, or quality) in a way that confounds helper effects and results in an absence of a relationship between helpers and breeding success. Results generally failed to support the hypothesis. Mean egg size was positively related to temperatures during the 10 days prior to egg-laying and negatively related to the food supply as indexed by the prior fall’s acorn crop, but there were no significant differences vis-à-vis helpers except for interactions with the acorn crop that only partly corresponded to those predicted. With respect to clutch size, females laid larger clutches when assisted by female helpers, opposite the pattern predicted. Although our results suggest that egg size is adjusted to particular ecological circumstances, we conclude that neither egg nor clutch size is adjusted in a way that confounds the apparent effects of helpers, as proposed by the concealed helper effects hypothesis.