Effects of Forest Fragmentation on Understory Hummingbirds in Amazonian Brazil

The behavior of Broad-tailed hummingbirds is altered by cycles of human activity in a forested area converted into agricultural land

Background

By changing the circumstances in which animals make their behavioral decisions, weekly cycles of human activity might cause changes in wildlife behavior. For example, when there is more human activity in a location, animals may become more vigilant, which can decrease the time they spend foraging, or roam farther from home, leading to increased home range size. Overall, there has been little exploration of how animal species living in locations that have undergone land use change are affected by the temporal dynamics of human activity levels. In this study, we aimed to analyze the effect of the weekend on agricultural activities and hummingbird territorial activity. We examined differences between weekdays and weekends in factors previously shown to follow weekly cyclical patterns, such as pedestrian presence, traffic, and the presence of domestic animals. We hypothesized that territorial hummingbirds would respond to these weekly cycles of human activity by altering their behavior.

Methods

We studied Broad-tailed hummingbird territories in forested areas that had been transformed to agriculture lands in central Mexico. We evaluated whether territorial individuals changed their behaviors (i.e., chases of intruders, foraging within their territory, number of intruders allowed to forage in the territory) in response to variation between weekdays and weekends in the number of pedestrians, cyclists, dogs, farm animals and vehicles.

Results

We found that the level of agriculture-related human activities showed a weekly cycle at our study site. On weekdays there was higher traffic of pedestrians, cyclists, dogs, farm animals and vehicles, compared to the weekends. Hummingbirds responded to these weekday-weekends differences by changing their territorial behavior. Compared to weekends, on weekdays hummingbirds showed a decrease in defense (number of chases) as well as the use of their territory (number of flowers visited), which allowed increased access to intruders (number of visited flowers by intruders).

Conclusions

Our findings suggest that variation in agriculture-related human activities between weekdays and weekends can alter the territorial behavior of hummingbirds. Behavioral shifts seem to be related to these human activity cycles, leading hummingbirds to reduce chases and feeding during weekdays when human activity is highest, but increasing both behaviors during times of minimal disturbance.

Elevated inbreeding in Heliconia tortuosa is determined by tropical forest stand age, isolation, and loss of hummingbird functional diversity

Forest conversion and habitat loss are major threats to biological diversity. Forest regeneration can mitigate the negative effects of old growth forest loss on species diversity, but less is known about the extent to which forest loss reduces genetic diversity in remnant populations and whether secondary forests play a role in the maintenance of genetic diversity. We quantified genetic diversity in a tropical hummingbird-pollinated understory herb, Heliconia tortuosa, across a landscape mosaic of primary and secondary forest regrowth. Using microsatellite genotypes from >850 adult and juvenile plants within 33 forest patches and extensive bird surveys, we examined the effect of contemporary and historical landscape features including forest age (primary vs. secondary forest), stand isolation, and pollinator assemblages on genetic diversity and levels of inbreeding in H. tortuosa. We found that inbreeding was up to 3x higher in secondary forest, and this effect was amplified with reductions in primary forest in the surrounding landscape through reduced observed heterozygosity in isolated fragments. Inbreeding in forest patches was negatively correlated with the local frequency of specialist long-distance foraging traplining hummingbirds. Traplining hummingbirds therefore appear to facilitate mating among unrelated plants - an inference we tested using empirically parameterized simulations. Higher levels of inbreeding in H. tortuosa are therefore associated with reduced functional diversity of hummingbirds in secondary forests and forest patches isolated from primary forests. Our findings suggest a cryptic consequence of primary forest loss and secondary forest regeneration through the disruption of mutualistic interactions resulting in the erosion of genetic diversity in a common understory plant.

The evolution, ecology, and conservation of hummingbirds and their interactions with flowering plants

The ecological co-dependency between plants and hummingbirds is a classic example of a mutualistic interaction: hummingbirds rely on floral nectar to fuel their rapid metabolisms, and more than 7000 plant species rely on hummingbirds for pollination. However, threats to hummingbirds are mounting, with 10% of 366 species considered globally threatened and 60% in decline. Despite the important ecological implications of these population declines, no recent review has examined plant-hummingbird interactions in the wider context of their evolution, ecology, and conservation. To provide this overview, we (i) assess the extent to which plants and hummingbirds have coevolved over millions of years, (ii) examine the mechanisms underlying plant-hummingbird interaction frequencies and hummingbird specialization, (iii) explore the factors driving the decline of hummingbird populations, and (iv) map out directions for future research and conservation. We find that, despite close associations between plants and hummingbirds, acquiring evidence for coevolution (versus one-sided adaptation) is difficult because data on fitness outcomes for both partners are required. Thus, linking plant-hummingbird interactions to plant reproduction is not only a major avenue for future coevolutionary work, but also for studies of interaction networks, which rarely incorporate pollinator effectiveness. Nevertheless, over the past decade, a growing body of literature on plant-hummingbird networks suggests that hummingbirds form relationships with plants primarily based on overlapping phenologies and trait-matching between bill length and flower length. On the other hand, species-level specialization appears to depend primarily on local community context, such as hummingbird abundance and nectar availability. Finally, although hummingbirds are commonly viewed as resilient opportunists that thrive in brushy habitats, we find that range size and forest dependency are key predictors of hummingbird extinction risk. A critical direction for future research is to examine how potential stressors - such as habitat loss and fragmentation, climate change, and introduction of non-native plants - may interact to affect hummingbirds and the plants they pollinate.

A Bird's-Eye View of Pollination: Biotic Interactions as Drivers of Adaptation and Community Change

Nectarivorous birds and bird-pollinated plants are linked by a network of interactions. Here I ask how these interactions influence evolution and community composition. I find near complete evidence for the effect of birds on plant evolution. Experiments show the process in action—birds select among floral phenotypes in a population—and comparative studies find the resulting pattern—bird-pollinated species have long-tubed, red flowers with large nectar volumes. Speciation is accomplished in one “magical” step when adaptation for bird pollination brings about divergent morphology and reproductive isolation. In contrast, evidence that plants drive bird evolution is fragmentary. Studies of selection on population-level variation are lacking, but the resulting pattern is clear—nectarivorous birds have evolved a remarkable number of times and often have long bills and brush-tipped or tubular tongues. At the level of the ecological guild, birds select among plant species via an effect on seed set and thus determine plant community composition. Plants simultaneously influence the relative fitness of bird species and thus determine the composition of the bird guild. Interaction partners may give one guild member a constant fitness advantage, resulting in competitive exclusion and community change, or may act as limiting resources that depress the fitness of frequent species, thus stabilizing community composition and allowing the coexistence of diversity within bird and plant guilds.

Land use change has stronger effects on functional diversity than taxonomic diversity in tropical Andean hummingbirds

Land use change modifies the environment at multiple spatial scales, and is a main driver of species declines and deterioration of ecosystem services. However, most of the research on the effects of land use change has focused on taxonomic diversity, while functional diversity, an important predictor of ecosystem services, is often neglected. We explored how local and landscape scale characteristics influence functional and taxonomic diversity of hummingbirds in the Andes Mountains in southern Ecuador. Data was collected in six landscapes along a land use gradient, from an almost intact landscape to one dominated by cattle pastures. We used point counts to sample hummingbirds from 2011 to 2012 to assessed how local factors (i.e., vegetation structure, flowering plants richness, nectar availability) and landscape factors (i.e., landscape heterogeneity, native vegetation cover) influenced taxonomic and functional diversity. Then, we analyzed environment – trait relationships (RLQ test) to explore how different hummingbird functional traits influenced species responses to these factors. Taxonomic and functional diversity of hummingbirds were positively associated with landscape heterogeneity but only functional diversity was positively related to native vegetation coverage. We found a weak response of taxonomic and functional diversity to land use change at the local scale. Environment‐trait associations showed that body mass of hummingbirds likely influenced species sensitivity to land use change. In conclusion, landscape heterogeneity created by land use change can positively influence hummingbird taxonomic and functional diversity; however, a reduction of native vegetation cover could decrease functional diversity. Given that functional diversity can mediate ecosystem services, the conservation of native vegetation cover could play a key role in the maintenance of hummingbird pollination services in the tropical Andes. Moreover, there are particular functional traits, such as body mass, that increase a species sensitivity to land use change.

Trait-based indicators of bird species sensitivity to habitat loss are effective within but not across data sets

Species' traits have been widely championed as the key to predicting which species are most threatened by habitat loss, yet previous work has failed to detect trends that are consistent enough to guide large-scale conservation and management. Here we explore whether traits and environmental variables predict species sensitivity to habitat loss across two data sets generated by independent avifaunal studies in the Atlantic Forest of Brazil, both of which detected a similar assemblage of species, and similar species-specific responses to habitat change, across an overlapping sample of sites. Specifically, we tested whether 25 distributional, climatic, ecological, behavioral, and morphological variables predict sensitivity to habitat loss among 196 bird species, both within and across studies, and when data were analysed as occurrence or abundance. We found that four to nine variables showed high explanatory power within a single study or data set, but none performed as strong predictors across all data sets. Our results demonstrate that the use of species traits to predict sensitivity to anthropogenic habitat loss can produce predictions that are species- and site-specific and not scalable to whole regions or biomes, and thus should be used with caution.

An Amazonian rainforest and its fragments as a laboratory of global change

We synthesize findings from one of the world's largest and longest-running experimental investigations, the Biological Dynamics of Forest Fragments Project (BDFFP). Spanning an area of ∼1000 km² in central Amazonia, the BDFFP was initially designed to evaluate the effects of fragment area on rainforest biodiversity and ecological processes. However, over its 38-year history to date the project has far transcended its original mission, and now focuses more broadly on landscape dynamics, forest regeneration, regional- and global-change phenomena, and their potential interactions and implications for Amazonian forest conservation. The project has yielded a wealth of insights into the ecological and environmental changes in fragmented forests. For instance, many rainforest species are naturally rare and hence are either missing entirely from many fragments or so sparsely represented as to have little chance of long-term survival. Additionally, edge effects are a prominent driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and a diversity of fauna. Even within our controlled study area, the landscape has been highly dynamic: for example, the matrix of vegetation surrounding fragments has changed markedly over time, succeeding from large cattle pastures or forest clearcuts to secondary regrowth forest. This, in turn, has influenced the dynamics of plant and animal communities and their trajectories of change over time. In general, fauna and flora have responded differently to fragmentation: the most locally extinction-prone animal species are those that have both large area requirements and low tolerance of the modified habitats surrounding fragments, whereas the most vulnerable plants are those that respond poorly to edge effects or chronic forest disturbances, and that rely on vulnerable animals for seed dispersal or pollination. Relative to intact forests, most fragments are hyperdynamic, with unstable or fluctuating populations of species in response to a variety of external vicissitudes. Rare weather events such as droughts, windstorms and floods have had strong impacts on fragments and left lasting legacies of change. Both forest fragments and the intact forests in our study area appear to be influenced by larger-scale environmental drivers operating at regional or global scales. These drivers are apparently increasing forest productivity and have led to concerted, widespread increases in forest dynamics and plant growth, shifts in tree-community composition, and increases in liana (woody vine) abundance. Such large-scale drivers are likely to interact synergistically with habitat fragmentation, exacerbating its effects for some species and ecological phenomena. Hence, the impacts of fragmentation on Amazonian biodiversity and ecosystem processes appear to be a consequence not only of local site features but also of broader changes occurring at landscape, regional and even global scales.

Life history and past demography maintain genetic structure, outcrossing rate, contemporary pollen gene flow of an understory herb in a highly fragmented rainforest

INTRODUCTION

Theory predicts that habitat fragmentation, by reducing population size and increasing isolation among remnant populations, can alter their genetic diversity and structure. A cascade of effects is expected: genetic drift and inbreeding after a population bottleneck, changes in biotic interactions that may affect, as in the case of plants, pollen dynamics, mating system, reproductive success. The detection of the effects of contemporary habitat fragmentation on the genetic structure of populations are conditioned by the magnitude of change, given the few number of generations since the onset of fragmentation, especially for long-lived organisms. However, the present-day genetic structure of populations may bear the signature of past demography events. Here, we examine the effects of rainforest fragmentation on the genetic diversity, population structure, mating system (outcrossing rate), indirect gene flow and contemporary pollen dynamics in the understory herb Aphelandra aurantiaca. Also, we assessed its present-day genetic structure under different past demographic scenarios.

METHODS

Twelve populations of A. aurantiaca were sampled in large (4), medium (3), and small (5) forest fragments in the lowland tropical rainforest at Los Tuxtlas region. Variation at 11 microsatellite loci was assessed in 28-30 reproductive plants per population. In two medium- and two large-size fragments we estimated the density of reproductive plants, and the mating system by analyzing the progeny of different mother plants per population.

RESULTS

Despite prevailing habitat fragmentation, populations of A. aurantiaca possess high genetic variation (He  = 0.61), weak genetic structure (Rst  = 0.037), and slight inbreeding in small fragments. Effective population sizes (Ne ) were large, but slightly lower in small fragments. Migrants derive mostly from large and medium size fragments. Gene dispersal is highly restricted but long distance gene dispersal events were detected. Aphelandra aurantiaca shows a mixed mating system (tm  = 0.81) and the outcrossing rate have not been affected by habitat fragmentation. A strong pollen pool structure was detected due to few effective pollen donors (Nep ) and low distance pollen movement, pointing that most plants received pollen from close neighbors. Past demographic fluctuations may have affected the present population genetic structure as Bayesian coalescent analysis revealed the signature of past population expansion, possibly during warmer conditions after the last glacial maximum.

DISCUSSION

Habitat fragmentation has not increased genetic differentiation or reduced genetic diversity of A. aurantiaca despite dozens of generations since the onset of fragmentation in the region of Los Tuxtlas. Instead, past population expansion is compatible with the lack of observed genetic structure. The predicted negative effects of rainforest fragmentation on genetic diversity and population structure of A. aurantiaca seem to have been buffered owing to its large effective populations and long-distance dispersal events. In particular, its mixed-mating system, mostly of outcrossing, suggests high efficiency of pollinators promoting connectivity and reducing inbreeding. However, some results point that the effects of fragmentation are underway, as two small fragments showed higher membership probabilities to their population of origin, suggesting genetic isolation. Our findings underscore the importance of fragment size to maintain genetic connectivity across the landscape.

Edge effects in the avifaunal community of riparian rain-forest tracts in Tropical North Queensland

Most evidence suggests anthropogenic edges negatively affect rain-forest bird communities but little has been done to test this in Australasia. In this study, avifaunal detection frequency, species richness and community composition were compared between the edge and interior and between flat and more complex-shaped edges of riparian rain-forest tracts in Tropical North Queensland. The detection frequency and richness of guilds based on diet, foraging strata and habitat specialism were also compared. This study detected 15.1% more birds at the rain-forest edge compared with the interior but no difference in species richness. Edge shape had no effect on detection frequency or richness. Many guilds (subcanopy, closed forest, frugivorous and insectivorous species) experienced increased detection frequency at the edge relative to the interior, but for some guilds this response was reduced (habitat generalists) or reversed (understorey and mixed-flock species) along complex edges. Overall community composition was affected by edge distance but not by edge shape. Edge habitat was shorter and had more open canopy than the interior, supporting habitat-based explanations for the observed avifaunal edge effects. These results suggest generally positive edge effects in Australian rain-forest bird communities, possibly reflecting local resource distributions or a disturbance-tolerant species pool.

Avian responses to selective logging shaped by species traits and logging practices

Selective logging is one of the most common forms of forest use in the tropics. Although the effects of selective logging on biodiversity have been widely studied, there is little agreement on the relationship between life-history traits and tolerance to logging. In this study, we assessed how species traits and logging practices combine to determine species responses to selective logging, based on over 4000 observations of the responses of nearly 1000 bird species to selective logging across the tropics. Our analysis shows that species traits, such as feeding group and body mass, and logging practices, such as time since logging and logging intensity, interact to influence a species' response to logging. Frugivores and insectivores were most adversely affected by logging and declined further with increasing logging intensity. Nectarivores and granivores responded positively to selective logging for the first two decades, after which their abundances decrease below pre-logging levels. Larger species of omnivores and granivores responded more positively to selective logging than smaller species from either feeding group, whereas this effect of body size was reversed for carnivores, herbivores, frugivores and insectivores. Most importantly, species most negatively impacted by selective logging had not recovered approximately 40 years after logging cessation. We conclude that selective timber harvest has the potential to cause large and long-lasting changes in avian biodiversity. However, our results suggest that the impacts can be mitigated to a certain extent through specific forest management strategies such as lengthening the rotation cycle and implementing reduced impact logging.

The importance of remnant native vegetation of Amazonian submontane forest for the conservation of lizards

Forest fragmentation affects animal population dynamics mainly by loss of habitat and disruption of animal movement. Lizard assemblages are affected by environmental changes, but, depending on their ecological needs, some species might be more vulnerable than others. The southern Amazon suffers accelerated anthropic actions replacing natural environments by farmland (crops and pasture). This region is considerably drier than most of the northern Amazon, with stational semi-deciduous forests fragmented and isolated by pasture, and crops to a lesser extent. Here we report data on lizard assemblages using semi-deciduous forests, forest edge and the surrounding pasture in the southern Amazon in Mato Grosso, Brazil. Lizards were collected in 21 forest fragments (41 to 7,035 ha) surrounded by pasture; using pitfall traps placed on a degradation gradient - from pasture inwards forest fragment (up to 200 m). We collected 242 individuals (14 species, seven families) in 6,300 trap-days. The pattern of species occurrence was largely nested and this nesting was associated with three habitat guilds (generalist, edge-tolerant, and forest species). Although there was no obvious fragmentation effect on lizards diversity community-wise, Hoplocercus spinosus, Bachia dorbignyi, Micrablepharus maximiliani and Kentropyx calcarta were more vulnerable to such effects than all other ten species collected. We verified that assemblages inhabiting pasture and forest edge are a nested subset of assemblages from the forest core. The remnant native vegetation is not distributed homogeneously and lizards species can persist in different parts of the landscape, therefore we recommend the protection of forest remnants as an important conservation action for lizards of the southern Amazon.

The conservation value of small, isolated fragments of lowland tropical rain forest

Deforestation is occurring at an alarming rate in the lowland tropics. In many tropical regions, rain forest is restricted to small (<100 ha), isolated fragments. While only the preservation of large areas of tropical rain forest can safeguard the complete biota, recent research has shown that a substantial number of forest species can persist for decades in fragmented forest, though large vertebrates are susceptible to habitat fragmentation. Inevitably, small fragments will become the last refuges of many rainforest species that are on the brink of extinction. In areas with little rain forest remaining, fragments can be the 'seeds' from which to re-establish extensive forest.

The hummingbird community and their floral resources in an urban forest remnant in Brazil

The temporal and spatial resource use among hummingbirds was studied over 13 months in an urban forest remnant (Prosa State Park: PSP) in Campo Grande, Mato Grosso do Sul, Brazil. Hummingbird visitation was recorded at three ornithophilous and eleven non-ornithophilous species. Flower density was roughly constant during the study period, with the density of non-ornithophilous flowers being higher than that of ornithophilous ones. Mean values of nectar volume and concentration were similar between ornithophilous and non-ornithophilous species. Eight hummingbird species were observed at PSP: Amazilia fimbriata, Anthracothorax nigricollis, Chlorostilbon lucidus, Eupetomena macroura, Hylocharis chrysura, Florisuga fusca, Thalurania furcata and an unidentified species. Hummingbird visit frequencies to ornithophilous and non-ornithophilous flowers were similar. However, some non-ornithophilous species received a higher number of visits, which seems to be related to their large number of open flowers per plant per day. The number of feedings bouts of hummingbirds increased with the total number of flowers observed per focal plant. All recorded species of hummingbirds visited non-ornithophilous flowers, predominantly melittophilous and generalised entomophilous flowers. Hummingbird species recorded at PSP may be viewed as generalists, visiting a large number of non-ornithophilous species. Despite being an urban forest, PSP is relatively rich in hummingbird species, suggesting that it provides important shelter and foraging sites for hummingbirds in such an environment.

Species loss, delayed numerical responses, and functional compensation in an antbird guild

When a community loses species through fragmentation, its total food consumption may drop. Compensatory responses of remaining species, whereby survivors assume roles of extinct competitors, may reduce the impact of species loss through numerical or functional responses. We measured compensatory responses in two remaining antbird species on Barro Colorado Island, Panama, four decades after the loss of their dominant competitor, the Ocellated Antbird, Phaenostictus mcleannani. We compared current abundances and behavior of these two species on Barro Colorado to those reported before the island lost Ocellated Antbirds, and to those in a nearby mainland population where all three species still exist as a space-for-time substitution. The smaller, more subordinate Spotted Antbird, Hylophylax naevioides, responded far more strongly than the larger Bicolored Antbird, Gymnopithys leucaspis, which is functionally more like the Ocellated Antbird. Islandwide density of Spotted Antbirds has more than doubled since the loss of Ocellated Antbirds. Moreover, Spotted Antbirds now spend so much more of their time following ant swarms that their metabolic biomass at these swarms has more than tripled since Ocellated Antbirds disappeared. These responses in Spotted Antbirds were apparently delayed by >20 years. Bicolored Antbirds have not increased substantially in islandwide density or metabolic biomass at ant swarms. We hypothesize that behavioral flexibility, as shown by Spotted Antbirds on Barro Colorado Island, is a major factor governing the extent to which fragmented ecosystems can buffer the impacts of species loss.

Changes in patch features may exacerbate or compensate for the effect of habitat loss on forest bird populations

One and a half centuries after Darwin visited Chiloe Island, what he described as "…an island covered by one great forest…" has lost two-thirds of its forested areas. At this biodiversity hotspot, forest surface is becoming increasingly fragmented due to unregulated logging, clearing for pastures and replacement by exotic tree plantations. Decrease in patch size, increased isolation and "edge effects" can influence the persistence of forest species in remnant fragments. We assessed how these variables affect local density for six forest birds, chosen to include the most important seed dispersers (four species) and bird pollinators (two species, one of which acts also as seed disperser), plus the most common insectivore (Aphrastura spinicauda). Based on cue-count point surveys (8 points per fragment), we estimated bird densities for each species in 22 forest fragments of varying size, shape, isolation and internal-habitat structure (e.g. tree size and epiphyte cover). Bird densities varied with fragment connectivity (three species) and shape (three species), but none of the species was significantly affected by patch size. Satellite image analyses revealed that, from 1985 to 2008, forested area decreased by 8.8% and the remaining forest fragments became 16% smaller, 58-73% more isolated and 11-50% more regular. During that period, bird density estimates for the northern part of Chiloé (covering an area of 1214.75 km(2)) decreased for one species (elaenia), increased for another two (chucao and hummingbird) and did not vary for three (rayadito, thrust and blackbird). For the first three species, changes in patch features respectively exacerbated, balanced and overcame the effects of forest loss on bird population size (landscape-level abundance). Hence, changes in patch features can modulate the effect of habitat fragmentation on forest birds, suggesting that spatial planning (guided by spatially-explicit models) can be an effective tool to facilitate their conservation.

Bird richness and composition in a Cerrado fragment in the State of São Paulo

Bird species richness is an important measure for monitoring biodiversity changes. We analysed avifauna richness and composition in a 472 ha protected cerrado fragment and surroundings at Fazenda Canchim (RL-CPPSE), São Carlos, in the State of São Paulo (SP). We carried out 95.1 hours of observation (22 visits) at irregular intervals from May 2004 to December 2006. Qualitative surveys were done walking through tracks inside the fragment and on the roads at its edge. We recorded 160 species, six of which were endemic to Cerrado domain, 22 migratory, seven threatened within the State of São Paulo, and two globally threatened. We found 28 species in the cerradão, 110 in the cerrado sensu stricto, 13 in the gallery forest, 26 in the reservoir border, 26 in pasturelands and sugar cane monoculture and 55 in an anthropic area. Most of the species had low frequency of occurrence in all vegetation forms. Insectivores were the major trophic category (46.9%), which is typical in tropical regions, and it is also related to resource availability. Omnivores followed with 19.4%, granivores with 8.8% and frugivores with 7.5%. We conclude that, despite its size and conservation status, our study area has a remarkable bird community and must be considered as a priority conservation area to preserve bird species in Sao Paulo State.

Abundance of Panamanian dry-forest birds along gradients of forest cover at multiple scales

Community structure and species’ abundances may be strongly correlated to patterns of forest cover, although such patterns are poorly known for tropical dry-forest birds, especially for those in Panamanian dry forests. Birds were distance-sampled during point counts in five dry-forest fragments in Panama. Distance from point count to forest edge and forest coverage at three spatial scales (500, 1000 and 2000-m radius) were compared as covariate predictors of the abundance of avian species and guilds. Each covariate was selected in at least two models of species or guild abundance. Abundance patterns were consistent with previously reported habitat associations for only two of seven open-habitat or forest-preferring species that showed forest cover-abundance relationships. Null models best described the abundance of all forest species and the subset of uncommon forest species. Thus many of these species appear insensitive to the forest-cover gradients studied. Total abundance of open-habitat-preferring species increased in dry forests with increasing forest coverage within 500 m, suggesting that the relationship between their abundance and vegetation structure are spatial-scale and habitat dependent. Nectarivores had lower abundance as forest cover within 1000 m increased, supporting previous claims that this group is tolerant of forest edges.

Tropical deforestation alters hummingbird movement patterns

Reduced pollination success, as a function of habitat loss and fragmentation, appears to be a global phenomenon. Disruption of pollinator movement is one hypothesis put forward to explain this pattern in pollen limitation. However, the small size of pollinators makes them very difficult to track; thus, knowledge of their movements is largely speculative. Using tiny radio transmitters (0.25 g), we translocated a generalist tropical 'trap-lining' hummingbird, the green hermit (Phaethornis guy), across agricultural and forested landscapes to test the hypothesis that movement is influenced by patterns of deforestation. Although, we found no difference in homing times between landscape types, return paths were on average 459+/-144 m (+/-s.e.) more direct in forested than agricultural landscapes. In addition, movement paths in agricultural landscapes contained 36+/-4 per cent more forest than the most direct route. Our findings suggest that this species can circumvent agricultural matrix to move among forest patches. Nevertheless, it is clear that movement of even a highly mobile species is strongly influenced by landscape disturbance. Maintaining landscape connectivity with forest corridors may be important for enhancing movement, and thus in facilitating pollen transfer.

Variation in pollinator assemblages in a fragmented landscape and its effects on reproductive stages of a self-incompatible treelet, Psychotria suterella (Rubiaceae)

Few studies of plant-pollinator interactions in fragmented landscapes evaluate the consequences of floral visitor variation on multiple stages of plant reproduction. Given that fragmentation potentially has positive or negative effects on different organisms, and that self-incompatible plant species depend on pollinators for sexual reproduction, differences in floral visitor assemblages may affect certain plant reproductive stages. We evaluated how pollinator assemblage, availability of floral resources, pollination, reproductive output, and seed and seedling performance of Psychotria suterella Muell. Arg. varied among three fragmentation categories: non-fragmented habitats, fragments connected by corridors, and isolated fragments. Richness and frequency of floral visitors were greater in fragments than in non-fragmented sites, resulting mainly from the addition of species typically found in disturbed areas. Although 24 species visited Psychotria suterella flowers, bumblebees were considered the most important pollinators, because they showed the highest frequency of visits and were present in eight out of ten sites. Additionally, the number of pollen tubes per flower per visit was lower in areas without bumblebees. The increased visitation in fragments seemed to enhance pollination slightly. However, fruit and seed output, germination, and seed and seedling mass were similar in non-fragmented sites, connected sites, and isolated fragments. Our results suggested that, even for a self-incompatible species, responses to habitat fragmentation at different stages of plant reproduction might be decoupled from the responses observed in floral visitors, if fruit set is not pollen limited. If all reproductive stages were considered, variation on the small scale was more important than the variation explained by fragmentation category. In spite of its self-incompatible breeding system, this plant-pollinator system showed resilience to habitat fragmentation, mainly as a result of high availability of potential mates to P. suterella individuals, absence of pollen limitation, and the presence of bumblebees (Bombus spp.) throughout this highly connected landscape.

Long-term landscape change and bird abundance in Amazonian rainforest fragments

The rainforests of the Amazon basin are being cut by humans at a rate >20,000 km2/year leading to smaller and more isolated patches of forest, with remaining fragments often in the range of 1-100 ha. We analyzed samples of understory birds collected over 20 years from a standardized mist-netting program in 1- to 100-ha rainforest fragments in a dynamic Amazonian landscape near Manaus, Brazil. Across bird guilds, the condition of second growth immediately surrounding fragments was often as important as fragment size or local forest cover in explaining variation in abundance. Some fragments surrounded by 100 m of open pasture showed reductions in insectivorous bird abundance of over 95%, even in landscapes dominated by continuous forest and old second growth. These extreme reductions may be typical throughout Amazonia in small (< or =10 ha), isolated fragments of rainforest. Abundance for some guilds returned to preisolation levels in 10- and 100-ha fragments connected to continuous forest by 20-year-old second growth. Our results show that the consequences of Amazonian forest loss cannot be accurately described without explicit consideration of vegetation dynamics in matrix habitat. Any dichotomous classification of the landscape into 'forest" and "nonforest" misses essential information about the matrix.

Avian community response to lowland tropical rainforest isolation: 40 years of change at La Selva Biological Station, Costa Rica

Since 1960, most of the forest surrounding the La Selva Biological Station, an intensively studied tropical research facility in Costa Rica, has been converted to agricultural uses. We used quantitative censuses and analysis of previously published categorical abundances to assess changes in the bird community, and we evaluated potential causes of species-specific changes by assessing their association with habitat, diet, participation in mixed-species flocks, and nest type. Approximately the same percentage of species increased as decreased in abundance from 1960 to 1999 (10-20% of all species, depending on method of assessment). Diet was the single most important trait associated with declining species. At least 50% of the species that declined have insectivorous diets. Use of forest habitat and participation in mixed-species flocks were also significant factors associated with declines, but nest type was unrelated to change in abundance. The species that increased in abundance tended to occur in open habitats and have omnivorous diets. These results reinforce the importance of several population risk factors associated with tropical understory insectivory and mixed-species flocking: patchy spatial distribution, low population density, large home range, and dietary specialization. La Selva's protected area (1611 ha), despite a forested connection on one boundary with a higher elevation national park, is apparently too small to maintain at least one major guild (understory insectivores). This first quantitative assessment of bird community change at La Selva highlights the need to intensify study of the mechanisms and consequences of biological diversity change in tropical forest fragments.

Effects of fragmentation on Thamnophilus stictocephalus (Aves, Thamnophilidae) in semideciduous forest of Alter-do-Chão, Pará

Effects of fragmentation on biodiversity have received much attention in recent decades, as fragmentation can greatly reduce viable areas for living organisms. We studied its effect on Thamnophilus stictocephalus (Thamnophilidae), an understory bird, in semideciduous forest fragments in Alter-do-Chão, Santarém, Pará. We tested whether the density of Thamnophilus stictocephalus was a function of fragment size and shape, density of vegetation, or arthropod biomass. Density of Thamnophilus was positively related to fragment size, but not to the other factors analyzed. Arthropod biomass was positively related to fragment size. The density of T. stictocephalus in fragments was significantly higher than it was in continuous forest. Fragmentation processes had a pronounced effect on the relative density of T. stictocephalus.

Distribution of sandflies (Diptera: Phlebotominae) in forest remnants and adjacent matrix habitats in Brazilian Amazonia

We studied the distribution of sandflies (Diptera: Phlebotominae) - insect vectors of several diseases, including leishmaniasis - at the interface between primary forest and cattle pasture and between primary forest and secondary forest (< 15 yr old) in Southern Brazilian Amazonia. Sandflies were collected by using a combination of light traps and traps having vertebrates as baits. Strong differences in abundance and species richness were found between primary forests and pastures. Very few sandfly species were found in the pastures, and those that were found generally occurred at lower densities when compared to the adjacent forest. At least one species (Lutzomyia lainsoni), however, can become extremely abundant in pastures, possibly depending on the presence of cattle and water bodies. Differences between primary forests and secondary forests were not so strong, although the latter usually had fewer species and lower population abundances. No species were exclusively found in pastures or secondary forests; the species present in these two habitats were a subset of those found in primary forests. The distance to the edge did not affect the abundance, richness and composition of sandfly species in primary forests. The abundance and richness of sandflies, however, was greater in forest edges facing pastures than those facing secondary forests. This pattern could not be explained by an influx of species and individuals from the adjacent pasture, suggesting the existence of in situ differences between the different types of forest edges studied.

Bird communities in two fragments of semideciduos forest in rural São Paulo state

A quali-quantitative survey was done in two fragments (75 and 100 ha) of semideciduous forest in rural São Paulo State. The aim was to characterize the bird community according to richness, abundance, and occurrence frequency in these areas. The qualitative survey showed 145 species in the Estação Ecológica de São Carlos - EESCar (Brotas) - and 173 in the Fazenda Santa Cecília - FSC (Patrocínio Paulista), while the quantitative survey showed the presence of 60 and 72 species in EESCar and FSC respectively. The isolation and the lower environmental quality of the EESCar fragment may be responsible for the lower number of species in this area compared to that of FSC. Abundance index value analysis (IPA) showed that both areas have a large number of species with low IPA and few species with intermediate or high IPA compared to the pattern observed in other surveys. At FSC, a larger number of occurrences of species in danger of extinction in São Paulo State was also observed. Apparently, the FSC fragment had better environmental quality for sheltering a larger number of species, including the endangered ones. The study of the community of birds is important in planning management and conservation of natural areas.