Phenology of Predation on Insects in a Tropical Forest: Temporal Variation in Attack Rate on Dummy Caterpillars

In communities of tropical insects, adult abundance tends to fluctuate widely, perhaps in part owing to predator–prey dynamics. Yet, temporal patterns of attack rates in tropical forest habitats have not been studied systematically; the identity of predators of insects in tropical forests is poorly known; and their responses to temporal variation in prey abundance have rarely been explored. We recorded incidence and shape of marks of attacks on dummy caterpillars (proxy of predation rate) in a sub‐montane tropical forest in Uganda during a yearlong experiment, and explored correlations with inferred caterpillar abundance. Applying the highest and lowest observed daily attack rates on clay dummies over a realistic duration of the larval stage of butterflies, indicates that the temporal variation in attack rate could cause more than 10‐fold temporal variation in caterpillar survival. Inferred predators were almost exclusively invertebrates, and beak marks of birds were very scarce. Attack rates by wasps varied more over time than those of ants. Attack rates on dummies peaked during the two wet seasons, and appeared congruent with inferred peaks in caterpillar density. This suggests (1) a functional response (predators shifting to more abundant resource) or adaptive timed phenology (predators timing activity or breeding to coincide with seasonal peaks in prey abundance) of predators, rather than a numerical response (predator populations increasing following peaks in prey abundance); and (2) that predation would dampen abundance fluctuations of tropical Lepidoptera communities.     

Nesting Success of Costa Rican Lowland Rain Forest Birds in Response to Edge and Isolation Effects

Although open-cup nesting birds generally face increased risk of nest depredation from forest edge predators and brood parasites in fragmented temperate landscapes, little information exists to assess such risks in tropical birds. We compared nesting success of real birds' nests in large and small forest fragments to a control site in Caribbean lowland wet forest of Costa Rica. Pooling across species, nesting success was significantly greater in unfragmented forest than in either small, isolated fragments or the La Selva Biological Reserve, which is at the tip of a forest 'peninsula' embedded in a largely deforested landscape. Nesting success in isolated fragments did not vary according to distance from edge, suggesting that predators in fragments act throughout these forest patches. The case for increased nest predation as a plausible mechanism to explain the documented decline of forest interior bird populations in this fragmented tropical landscape is enhanced by a simple demographic model that suggests nesting success is likely too low to maintain populations at La Selva and in the fragments. The fact that the large (> 1000 ha) La Selva forest reserve is experiencing nest predation rates similar to those in much smaller fragments is cause for concern. Our results make a strong case for additional studies to document the identities of nest predators in both fragmented and unfragmented forests in such tropical forest landscapes.     

营巢类型、巢捕食和窝卵数对高寒草甸雀形目雏鸟生长期的影响

根据1998—2001年高寒草甸10种雀形目鸟类的窝卵数、雏期和巢捕食数据,以Logistic方程拟合雏鸟生长过程,并计算出有关生长率参数;根据营巢类型将10种雀形目鸟划分为开放或半开放类群(GOB)和全封闭穴居类群(HCB)两类,将把雏鸟的生长过程划分为3个生长期(缓增期、快增期和渐增期)。3个生长期占雏期的比例因营巢类型而异,GOB类群快增期>渐增期>缓增期;HCB类群渐增期>快增期>缓增期。分析营巢类型、巢捕食和窝卵数与各生长期之间的关系,结果表明3个生长期的体重积累占离巢时体重的比例因巢型不同而有显著差异;营巢类型和巢捕食显著影响各生长期占雏期的比例和体重积累占离巢时体重的比例;窝卵数影响快增期和渐增期长度,而不影响缓增期长度。快增期体重积累与渐增期的生长率不相关,但与渐增期长度显著相关。因此,前期的能量积累不影响后期生长率,而影响后期生长的长度。该结果进一步印证在晚成鸟中不存在补偿性生长。     

Effects of Native and Non-Native Grassland Plant Communities on Breeding Passerine Birds: Implications for Restoration of Northwest Bunchgrass Prairie

One common problem encountered when restoring grasslands is the prominence of non-native plant species. It is unclear what effect non-native plants have on habitat quality of grassland passerines, which are among the most imperiled groups of birds. In 2004 and 2005, we compared patterns of avian reproduction and the mechanisms that might influence those patterns across a gradient of 13 grasslands in the Zumwalt Prairie in northeastern Oregon that vary in the degree of non-native plant cover (0.9–53.4%). We monitored the fate of 201 nests of all the breeding species in these pastures and found no association of percent non-native cover with nest densities, clutch size, productivity, nest survival, and nestling size. Regardless of the degree of non-native cover, birds primarily fed on Coleoptera, Orthoptera, and Araneae. But as percent non-native cover in the pastures increased, Orthoptera made up a greater proportion of diet and Coleoptera made up a smaller proportion. These diet switches were not the result of changes in terrestrial invertebrate abundance but may be related to decreases in percent bare ground associated with increasing cover of non-native vegetation. Measures of nest crypticity were not associated with cover of non-native vegetation, suggesting that predation risk may not increase with increased cover of non-native vegetation. Thus, the study results show that increased non-native cover is not associated with reduced food supplies or increased predation risk for nesting birds, supporting the growing body of evidence that grasslands with a mix of native and non-native vegetation can provide suitable habitat for native grassland breeding birds.     

Soil Effects on Forest Structure and Diversity in a Moist and a Dry Tropical Forest

Soil characteristics are important drivers of variation in wet tropical forest structure and diversity, but few studies have evaluated these relationships in drier forest types. Using tree and soil data from 48 and 32 1 ha plots, respectively, in a Bolivian moist and dry forest, we asked how soil conditions affect forest structure and diversity within each of the two forest types. After correcting for spatial effects, soil‐vegetation relationships differed between the dry and the moist forest, being strongest in the dry forest. Furthermore, we hypothesized that soil nutrients would play a more important role in the moist forest than in the dry forest because vegetation in the moist forest is less constrained by water availability and thus can show its full potential response to soil fertility. However, contrary to our expectations, we found that soil fertility explained a larger number of forest variables in the dry forest (50 percent) than in the moist forest (17 percent). Shannon diversity declined with soil fertility at both sites, probably because the most dominant, shade‐tolerant species strongly increased in abundance as soil fertility increased.     

The Role of Mammals in Creating and Modifying Seedshadows in Tropical Forests and Some Possible Consequences of Their Elimination

Mammal populations are increasingly hunted, yet the consequences of their disappearance from tropical forests have only recently been explored. Here, we summarize current research on the role of mammals in seed dispersal and postdispersal processes, such as seed predation and secondary dispersal, in different tropical regions. We evaluate how mammal features influence seedshadows and ultimately forest regeneration. Finally, we discuss the potential effect of changes in seedshadows caused by the elimination of many medium- and large-sized mammals. The complex role that mammals play in creating and modifying seedshadows in tropical forests cannot be easily quantified, and in this review we emphasize the variation that exists both within and among mammal taxa and across continents. To bridge this gap in information, we suggest that more studies should evaluate the relative importance of the disappearance of both seed dispersers and seed predators for particular plant species so that we may begin to understand the balance between these two influences. We also suggest that future studies identify ecological redundancy in nonhunted vertebrates within any particular community to evaluate compensatory behavior that may help ameliorate some of the negative effects of hunting of large and medium mammals.     

The Role of Landscape Patterns of Habitat Types on Plant Species Diversity of a Tropical Forest in Mexico

The relationships among landscape characteristics and plant diversity in tropical forests may be used to predict biodiversity. To identify and characterize them, the number of species, as well as Shannon and Simpson diversity indices were calculated from 157 sampling quadrats (17,941 individuals sampled) while the vegetation classes were obtained from multi-spectral satellite image classification in four landscapes located in the southeast of Quintana Roo, Mexico. The mean number of species of trees, shrubs and vines as well as the mean value of the total number of species and the other two diversity indices were calculated for four vegetation classes in every one of the four landscapes. In addition, the relationships between landscape patterns metrics of patch types and diversity indices were explored. The multiple statistical analyses revealed significant predictor variables for the three diversity indices. Moreover, the shape, similarity and edge contrast metrics of patch types might serve as useful indicators for the number of species and the other two diversity variables at the landscape scale. Although the association between the three diversity indices and patch types metrics showed similar behavior, some differences were appreciated. The Shannon diversity index, with its greater sensitivity to rare species, should be considered as having a greater importance in interpretation analysis than Simpson index.     

天际岭森林公园夏季鸟类群落调查及多样性研究

2003年夏季,对天际岭国家森林公园的鸟类群落进行了调查,共发现有鸟类39种,隶属于11目26科34属.通过对不同地区鸟类群落的比较研究,结果表明植物群落的垂直结构和水平格局对鸟类群落的多样性具有直接影响.     

Tracing the Origin of Dietary Protein in Tropical Dry Forest Birds1

Fundamental to our understanding of the ecology of animal communities in the tropics is knowledge of the effect of seasonal changes in the abundance of food sources in consumer diets. We determined stable‐isotope composition (¹³C/¹²C and ¹⁵N/¹⁴N) in whole blood of 14 resident avian species in a tropical dry forest to quantify the origin of their assimilated protein. We used a probabilistic approach (IsoSource) to estimate the relative contribution of C₃ plants, CAM‐C₄ plants, C₃ insects, and CAM‐C₄ insects during the dry and rainy seasons. IsoSource iteratively creates each possible combination of source contribution and produces a distribution of all feasible combinations that adequately predict the observed isotopic signature of the consumer. Granivore–frugivores and granivore–frugivore–insectivores were modeled as predominantly dependent upon plants whereas insectivorous birds were modeled to derive protein almost exclusively from insects. Between these extremes there were several species using mixed diets such as insectivore–frugivores or insectivore–granivores. In most species, virtually all assimilated food was of C₃ origin with the exception of Ruddy Ground‐Doves (Columbina talpacoti) in which CAM or C₄ plants contributed significantly. Seasonal changes in relative food source contribution were followed in eight species of birds. Of these species, White‐tipped Doves (Leptotila verreauxi), Grayish Saltators (Saltator coerulescens), and Social Flycatchers (Myiozetetes similis) increased their use of insects in the rainy season, in contrast to Great Kiskadees (Pitangus sulphuratus), which decreased their use of insects. Our study suggests that that diverse strategies are used by various avian species to obtain dietary proteins within seasonal habitats.     

Herbivory Rate of Leaf-Cutting Ants in a Tropical Moist Forest in Panama at the Population and Ecosystem Scales

Leaf-cutting ants are frequently characterized as the major herbivores in the Neotropics, but quantitative data to back up this assumption are scarce. In this study, the consumption and herbivory rates for the entire leaf-cutting ant ( Atta colombica , Formicidae) population in an old secondary forest on Barro Colorado Island (BCI) in Panama were determined over 15 mo (on average 49 colonies). The number of harvested leaf fragments was calculated from monthly refuse deposition rates of the colonies and the regression between refuse deposition and harvesting rates. The inclusion of fragment characteristics (proportion of leaf fragments in the harvest, average fragment weight, and area) allowed us to calculate consumption and herbivory rates at colony, population, and ecosystem levels. The A. colombica population harvested 13.2 tons of biomass/yr and 13.1 ha of leaf area/yr, and deposited 9.4 tons of refuse material/yr. Rates varied considerably among colonies. At the ecosystem level, i.e. , per forest area, herbivory rates were 132 kg biomass/ha/yr and 1310 m² foliage/ha/yr. For the area on BCI where A. colombica occurs (100 ha), this is equivalent to 2.1 percent of the foliage area in the forest or 1.7 percent of the annual leaf-area production. This value is considerably lower than previously published estimates of leaf-cutting ant herbivory rates in tropical forests.     

Combined Effects of Host Plant Quality and Predation on a Tropical Lepidopteran: A Comparison between Treefall Gaps and the Understory in Panama

In tropical forests, light‐gaps created from treefalls are a frequent source of habitat heterogeneity. The increase in productivity, through gap formation, can alter food quality, predation and their impact on insect herbivores. We hypothesized that in gaps, herbivores would be less resource‐limited and more predator limited, whereas in the understory, we predicted the reverse. In this study, we investigate the combined effects of food quality and predation on the lepidopteran larva Zunacetha annulata feeding on its host plant Hybanthus prunifolius in two habitats; sunny treefall gaps and the shaded understory in Panama. In bioassays, Z. annulata feeding on sun leaves ate 22 percent less leaf area, grew 25 percent faster, and had higher pupal weights than larvae feeding on shade leaves. However, shade leaves had higher nitrogen content and specific leaf area. In gaps, predation was 26.4 percent compared to 13.8 percent in the understory. Larvae on understory plants traveled greater distances and spent more time searching and traveling than larvae on gap plants. These differences in behavior are consistent with lower predation risk and lower quality food in the understory. Using data from bioassays and field experiments we calculated 0.22 percent and 1.02 percent survival to adulthood for larvae in gaps and the understory, respectively. In conclusion, although these habitats were in close proximity, we found that larvae in the understory are more resource‐limited and larvae in gaps are more predator limited.     

Restoration of Fragmented Landscapes for the Conservation of Birds: A General Framework and Specific Recommendations for Urbanizing Landscapes

Humans fragment landscapes to the detriment of wildlife. We review why fragmentation is detrimental to wildlife (especially birds), review the effects of urbanization on birds inhabiting nearby native habitats, suggest how restoration ecologists can minimize these effects, and discuss future research needs. We emphasize the importance of individual fitness to determining community composition. This means that reproduction, survivorship, and dispersal (not simply community composition) must be maintained, restored, and monitored. We suggest that the severity of the effects of fragmentation are determined by (1) the natural disturbance regime, (2) the similarity of the anthropogenic matrix to the natural matrix, and (3) the persistence of the anthropogenic change. As a result, urbanization is likely to produce greater effects of fragmentation than either agriculture or timber harvest. Restoration ecologists, land managers, and urban planners can help maintain native birds in fragmented landscapes by a combination of short‐ and long‐term actions designed to restore ecological function (not just shape and structure) to fragments, including: (1) maintaining native vegetation, deadwood, and other nesting structures in the fragment, (2) managing the landscape surrounding the fragment (matrix), not just the fragment, (3) making the matrix more like the native habitat fragments, (4) increasing the foliage height diversity within fragments, (5) designing buffers that reduce penetration of undesirable agents from the matrix, (6) recognizing that human activity is not compatible with interior conditions, (7) actively managing mammal populations in fragments, (8) discouraging open lawn on public and private property, (9) providing statutory recognition of the value of complexes of small wetlands, (10) integrating urban parks into the native habitat system, (11) anticipating urbanization and seeking creative ways to increase native habitat and manage it collectively, (12) reducing the growing effects of urbanization on once remote natural areas, (13) realizing that fragments may be best suited to conserve only a few species, (14) developing monitoring programs that measure fitness, and (15) developing a new educational paradigm.     

The Plight of Large Animals in Tropical Forests and the Consequences for Plant Regeneration

We introduce a special section that addresses the bushmeat or wild meat crisis, its direct impact on game species, and its indirect impact on plants in tropical forests.     

Susceptibility of Tree Seedlings to Biotic and Abiotic Hazards in the Understory of a Moist Tropical Forest in Panama

We evaluated temporal patterns of seedling survival of eight Neotropical tree species generated under multiple abiotic and biotic hazards (vertebrates, disease, litterfall) in the forest understory on Barro Colorado Island, Panama. Seedlings were transplanted at first leaf expansion in low densities along a 6-km transect and damage and mortality were recorded for 1 yr. We also planted and monitored small and large artificial seedlings to estimate physical disturbance regimes. During 0–2 mo after transplant, vertebrate consumers of reserve cotyledons caused high mortality of real seedlings, but little damage to artificial seedlings. On real seedlings after 2 mo, disease became an important agent of mortality, despite a decrease in overall mortality rates. Damage by litterfall remained relatively low during the 1-yr study period. Survival ranks among species showed ontogenetic shifts over time, as species changed susceptibility to the mortality agents. Survival after 2 mo was positively correlated with stem toughness, not because species with tough stems were less likely to receive mechanical damage, but because they survived better after receiving mechanical damage. Within each transplant station, artificial seedlings were not good predictors of litterfall damage experienced by real seedlings. Forest-wide litterfall damage level, however, was similar for both real and artificial seedlings ( ca 10%/yr), a moderate level compared to other tropical forests. In conclusion, species traits including biomechanical traits interact to create complex temporal patterns of first year seedling survival, resulting in ontogenetic shifts that largely reflect changes in the relative importance of vertebrate consumers relative to other hazards.     

Variation in Seedling Density and Seed Predation Indicators for the Emergent Tree Dipteryx panamensis in Continuous and Fragmented Rain Forest1

Seedling density and the condition of stony endocarps of the tree Dipteryx panamensis were assessed in protected continuous forest and two forest fragments exposed to hunting and selective logging. Seedling density was higher in forest fragments than in continuous forest, while more whole endocarps and fewer chewed and half endocarps were found in fragments, indicating lower seed predation at fragment sites. These findings appear to contradict two earlier D. panamensis studies and we discuss methodological differences that could account for our disparate results. Hunting and fragmentation effects on mammal populations are suggested as a cause for the altered recruitment pattern in fragments.     

Consequences of pre-dispersal damage by insects for the dispersal and recruitment of mangroves

Herbivores may enhance plant recruitment, but such positive interactions may be overlooked in favour of obvious negative effects of herbivory on propagules. My objective was to determine whether larval insects that feed and develop within fruit of the mangrove Avicennia marina act as mutualist herbivores by increasing the dispersal of propagules without affecting their viability and emerging successfully as adults following dispersal of the propagule by water. Surveys revealed that frugivory is common throughout the mangrove forest, and fruit had up to six exit holes where larvae had emerged as adults. Larval insects did not affect the flotation of propagules with pericarps, a thin structure that provides buoyancy for dispersal by water. In contrast, after simulating germination by removing the pericarp, the majority of propagules with three exit holes floated on average for 20 h longer than those without exit holes, which sank immediately. Based on this evidence that frugivory could increase the dispersal potential of propagules, I predicted that propagules consumed by larval insects should disperse farther than undamaged propagules, and this was tested by quantifying the potential viability of propagules stranded on beaches at increasing distances (up to 20 km) from mangrove forests. Flies and moths emerged as adults after being transported tens of kilometres within mangrove propagules, revealing a novel mode of dispersal. Proportionally fewer potentially viable propagules were supplied to beaches at increasing distances from mangrove forests, however, indicating that larval insects negatively affect recruitment and are thus not acting as mutualist herbivores. Nevertheless, when transported back to the mangrove forest, seedlings established from propagules damaged by larval insects and stranded on beaches. Therefore, although frugivory does not preclude mangrove recruitment, its negative effects in the pre-dispersal environment may be intensified with increasing dispersal distance, thus limiting the long-distance supply of propagules and recruitment of mangroves.     

From feces to data: A metabarcoding method for analyzing consumed and available prey in a bird‐insect food web

Diets play a key role in understanding trophic interactions. Knowing the actual structure of food webs contributes greatly to our understanding of biodiversity and ecosystem functioning. The research of prey preferences of different predators requires knowledge not only of the prey consumed, but also of what is available. In this study, we applied DNA metabarcoding to analyze the diet of 4 bird species (willow tits Poecile montanus, Siberian tits Poecile cinctus, great tits Parus major and blue tits Cyanistes caeruleus) by using the feces of nestlings. The availability of their assumed prey (Lepidoptera) was determined from feces of larvae (frass) collected from the main foraging habitat, birch (Betula spp.) canopy. We identified 53 prey species from the nestling feces, of which 11 (21%) were also detected from the frass samples (eight lepidopterans). Approximately 80% of identified prey species in the nestling feces represented lepidopterans, which is in line with the earlier studies on the parids' diet. A subsequent laboratory experiment showed a threshold for fecal sample size and the barcoding success, suggesting that the smallest frass samples do not contain enough larval DNA to be detected by high‐throughput sequencing. To summarize, we apply metabarcoding for the first time in a combined approach to identify available prey (through frass) and consumed prey (via nestling feces), expanding the scope and precision for future dietary studies on insectivorous birds.     

Use of Fruiting Trees by Birds in Continuous Forest and Riparian Forest Remnants in Los Tuxtlas,Veracruz, Mexico1

The composition of plant species in fragmented landscapes may be influenced by the pattern of visitation by birds to fruiting trees and by the movement of seeds among and within fragments. We compared bird visitation patterns to two tree species (Dendropanax arboreus, Araliaceae; Bursera simaruba, Burseraceae) in continuous forest and remnants of riparian vegetation in a region dominated by pasture in Los Tuxtlas, Veracruz, Mexico. We quantified frequency of visitation, fruit consumption, consistency of visitation (percentage of total tree observation periods during which a given bird species was recorded), and species composition of birds at individuals of both tree species in continuous forest and riparian remnants. Bird visitation rate, species richness, and fruit consumption rates were similar within both tree species in the two habitats. Species assemblages at D. arboreus were different between continuous forest and remnants. Species assemblages at B. simaruba did not differ by habitat. Our results demonstrate that habitat disturbance may influence avian visitation patterns, which may in turn affect subsequent recruitment patterns in some tree species. Our results, however, were not consistent between the tree species, suggesting that it is difficult to generalize concerning the effects of forest disturbance on avian species assemblages in fruiting trees.     

北京野生水鸟迁徙规律及其监测策略初探

2005年全球暴发的禽流感疫情备受世界关注,候鸟带毒且野生水鸟是禽流感病毒的天然储库已被世界公认,我国野生动物疫源疫病监测工作已被提到重要议事日程.通过对2006～2008年监测数据的分析,发现北京市野生水鸟春季迁徙从2月下旬开始,4月初达到迁徙高峰;9月下旬开始秋季南迁,11月下旬达到迁徙高峰.并分别对北京地区雁鸭类、鹬鸻类、鹭类的迁徙规律进行了分析;根据北京的气候特点分析了野生水鸟的分布和迁徙特点;根据禽流感病毒与温度的关系,提出了北京的重点监测时期及物种.