Protected from fire,but not from harm: seedling emergence of savanna grasses is constrained by burial depth

ABSTRACT

Background

The Cerrado is a fire-prone Neotropical savanna and grass seeds are the main component of the soil seed bank. Although grass seeds are presumed to tolerate heat pulses during fires, the assumption that these seeds will be recruited may be an overestimation, since it does not account for factors that limit seedling emergence from the soil.     

Neotropical Primates in a Regenerating Costa Rican Dry Forest: A Comparison of Howler and Capuchin Population Patterns

Few data exist on how primate populations return to regenerating tropical forests. We compare the ways that two populations of neotropical monkeys, Alouatta palliata and Cebus capucinus, expanded over a 28-year period after the establishment of Santa Rosa National Park on reclaimed ranchlands in Costa Rica. We found that both howler and capuchin populations increased substantially in size subsequent to protection, but the howler population grew faster. This is likely due to their faster-paced life-history pattern than that of capuchins. The howler population increased mainly via the establishment of many new groups, whereas the capuchins expanded mainly by increasing the size of existing groups. We related this finding to the fact that capuchins are limited largely by their need to drink from water holes during the dry seasons whereas howlers are limited principally by their preference for larger-sized trees that occur in older forests. Proportions of adult male capuchins increased significantly during our study, likely due to skewed sex ratio at birth or male-biased immigration into the protected park or both factors. Our main finding is that, in as short a time period as 28 years, we can substantially enhance the size of monkey populations by allowing the regeneration of tropical forest. Furthermore, we provide a preliminary interpretation of how extrinsic factors—deforestation, hunting, crop-spraying, destruction of the watershed—and intrinsic variables, e.g., pace of reproduction; diet, differentially affect not only each species' vulnerability to extinction but also its capacity to recover when human disturbances are minimized.     

Age‐specific responses to spring temperature in a migratory songbird: older females attempt more broods in warmer springs

Increasing global temperature has led to an interest in plasticity in the timing of annual events; however, little is known about the demographic consequences of changing phenology. Annual reproductive success varies significantly among individuals within a population, and some of that variation has to do with the number of broods attempted by reproducing adults. In birds, female age and the timing of reproduction are often predictors of multiple breeding. We hypothesize that double brooding rates may be affected by spring temperature and that the response may vary with female age. We used a long‐term reproductive data set for a migratory songbird, the prothonotary warbler (Protonotaria citrea) to assess which factors influence (a) an individual female's probability of double brooding and (b) the annual variation in population‐level double brooding rates. We found that older and earlier nesting birds are more likely to double brood, and that there is no evidence for senescence with regard to this trait such that the oldest females were most likely to double brood. Previous experience with double brooding (i.e., whether the female double brooded in the previous year) significantly increased the probability of doing so again. When assessing annual variation in the double brooding rate, we found an interaction between spring temperature and the proportion of older females in the population. Specifically, older females are more likely to double brood in years with warmer springs, but this relationship was not seen for younger females. Previous studies have shown that warmer temperatures lead to earlier and narrower peaks in resources and we hypothesize that these peaks are more available to older and earlier arriving females, enabling them to successfully raise more than one brood in a season. Understanding how different age classes respond to changing environmental conditions will be imperative to managing declining species.     

A descriptive and analytical study of four neotropical drosophilid communities

Drosophilid communities living in four different physiographical regions of the state of Rio Grande do Sul (27°/34°S; 49.7°/57.5°W), Brazil, were analysed. Ignoring cosmopolitan species, this is about the southern limit of the majority of typically neotropical Drosophila species distribution. Numerical fluctuations of the most frequent species populations from each place were investigated in relation to climatic data and trophic-resource availability. Of the four locations studied, Turvo is remarkable for being an enormous ecological reserve covered with subtropical perennially rainy forest, and for having stable weather conditions. Guaiba, on the other hand, is a more climatically unstable place, with unpredictable and more scarce resources. In Turvo, the community structure is shaped by the dominance of Drosophila willistoni and a low species diversity throughout the year. Low average niche-breadth and niche-overlap indices have also been found at feeding and breeding site levels. Guaíba showed the highest species-diversity levels and was better exploited by D. simulans, a cosmopolitan species with a well-known colonizing capacity. High niche breadth and overlap indices were characteristic for most species at this place. Results are discussed in the light of the communities' species composition and of environmental factors.