Focal Tree Research Articles

The effects of soil fertility and scale on competition in ponderosa pine

The intensity of competition between neighboring trees depends on local stand structure, and the influence of stand structure may vary across gradients in soil resource supplies. We used model selection techniques to look for variation in the nature and intensity of interactions between trees along a gradient of soil nitrogen supply in a 9-ha stand of old-growth ponderosa pine (Pinus ponderosa) in Colorado, USA. We used spatially explicit competition indexes to describe the interactions between trees and developed individual tree growth models to look at how soil nitrogen (N) supply affects competition. The growth of focal trees showed an asymmetric influence of neighbors up to 14-m distance. The predictive ability of our growth models more than doubled (to an r 2 = 0.69) as the size of the neighborhood used to calculate the competition indexes increased from a 2-m to a 14-m radius. The supply of soil nitrogen modified competition, with increasing N enhancing competition from neighbors. Neighborhood structure and soil resource supplies jointly influenced the growth of individual trees, but at different scales. Tree interactions are both spatially and temporally complex and may be studied most usefully with explicit evaluation of gradients in resource availability.

Frugivory in Canopy Plants in a Western Amazonian Forest: Dispersal Systems, Phylogenetic Ensembles and Keystone Plants.

Frugivory is a widespread mutualistic interaction in which frugivores obtain nutritional resources while favoring plant recruitment through their seed dispersal services. Nonetheless, how these complex interactions are organized in diverse communities, such as tropical forests, is not fully understood. In this study we evaluated the existence of plant-frugivore sub-assemblages and their phylogenetic organization in an undisturbed western Amazonian forest in Colombia. We also explored for potential keystone plants, based on network analyses and an estimate of the amount of fruit going from plants to frugivores. We carried out diurnal observations on 73 canopy plant species during a period of two years. During focal tree sampling, we recorded frugivore identity, the duration of each individual visit, and feeding rates. We did not find support for the existence of sub assemblages, such as specialized vs. generalized dispersal systems. Visitation rates on the vast majority of canopy species were associated with the relative abundance of frugivores, in which ateline monkeys (i.e. Lagothrix and Ateles) played the most important roles. All fruiting plants were visited by a variety of frugivores and the phylogenetic assemblage was random in more than 67% of the cases. In cases of aggregation, the plant species were consumed by only primates or only birds, and filters were associated with fruit protection and likely chemical content. Plants suggested as keystone species based on the amount of pulp going from plants to frugivores differ from those suggested based on network approaches. Our results suggest that in tropical forests most tree-frugivore interactions are generalized, and abundance should be taken into account when assessing the most important plants for frugivores.

Landscape effects on jay foraging behavior decrease acorn dispersal services in dehesas

Dehesas are savanna-like, oak woodlands with a high conservation value that are threatened by chronic regeneration failure. Acorn dispersal by Eurasian jays (Garrulus glandarius) is vital for oak recruitment although jay preference for continuous forests may condition this mutualism in dehesas. In this study, we evaluated whether the acorn dispersal services provided by jays to oaks differed between both habitats and assessed factors that could potentially drive such differences. We (1) monitored acorn removal rates at feeders located close to focal trees in a holm oak (Quercus ilex) forest and in a nearby dehesa over a 6-year period; (2) measured the spatial traits of focal trees and their acorn production; and (3) monitored dispersal distances and microhabitat selection for acorn caching during 2012.Our results indicated that jays were able to exploit dehesas located close to forest habitats, but did so infrequently and as a secondary food source (acorn removal rates were six times lower in dehesa than in nearby forests). This likely occurred because dehesas did not offer new or more abundant food sources on a landscape scale. In forests, tree choice was driven by crop traits while in dehesas it was driven by spatial location. Jays preferentially foraged at dehesa trees near forest patches and aggregated to other trees, regardless of crop traits. Acorns were mobilized four times closer in dehesas, and seeds were preferentially cached in unsuitable microhabitats for seedling establishment. Our results suggest that (i) distance to forest habitats and tree isolation effects on jay foraging behavior reduces their dispersal services in dehesas as compared to nearby forests, and (ii) practices designed to enhance acorn dispersal by jays in this habitat should focus on the maintenance or creation of forest patches interspersed within dehesa areas.

Implications of Climate Change for Turnover in Forest Composition

Predicting how climate change will influence forests is challenging. Forest communities are expected to lose cold-adapted trees near their low latitude/elevation range limits, while warm-adapted trees should increase in abundance near their high latitude/elevation limits ( i.e., ‘thermophilization’). However, slow-growing and long-lived trees, paired with climatic sensitivities that differ by species could add complexity to these predictions. To address these possibilities, we use demographic data collected from Mount Rainier National Park to examine: 1) the likelihood of rapid population growth or decline near range limits; 2) differences in climatic sensitivities between tree species at juvenile and adult stages; and 3) whether forest communities have already changed in response to recent warming. Our results suggest focal species are unlikely to shift their ranges rapidly with warming because recruit densities are low and time to reproductive maturity slow near upper range limits, while survival of adult trees is high near lower range limits. Additionally, focal tree species differ in the magnitude and strength of responses at seed and adult stages to climatic factors likely to be altered by warming. Consistent with these findings, shifts in forest community composition over the last 35 years were small, and not consistent with thermophilization predictions. In all, results imply that climate change will only have small, but unpredictable impacts on forest composition in the near-term. We discuss the possibility of much larger changes in forest composition with future climate change, if the drastically different climate regimes projected for the region fundamentally alter demographic processes and disturbance regimes.

Do birds see the forest for the trees? Scale-dependent effects of tree diversity on avian predation of artificial larvae.

The enemies hypothesis states that reduced insect herbivory in mixed-species stands can be attributed to more effective top-down control by predators with increasing plant diversity. Although evidence for this mechanism exists for invertebrate predators, studies on avian predation are comparatively rare and have not explicitly tested the effects of diversity at different spatial scales, even though heterogeneity at macro- and micro-scales can influence bird foraging selection. We studied bird predation in an established forest diversity experiment in SW Finland, using artificial larvae installed on birch, alder and pine trees. Effects of tree species diversity and densities on bird predation were tested at two different scales: between plots and within the neighbourhood around focal trees. At the neighbourhood scale, birds preferentially foraged on focal trees surrounded by a higher diversity of neighbours. However, predation rates did not increase with tree species richness at the plot level and were instead negatively affected by tree height variation within the plot. The highest probability of predation was observed on pine, and rates of predation increased with the density of pine regardless of scale. Strong tree species preferences observed may be due to a combination of innate bird species preferences and opportunistic foraging on profitable-looking artificial prey. This study therefore finds partial support for the enemies hypothesis and highlights the importance of spatial scale and focal tree species in modifying trophic interactions between avian predators and insect herbivores in forest ecosystems.

Single-Species Detection With Airborne Imaging Spectroscopy Data: A Comparison of Support Vector Techniques

Progress in mapping plant species remotely with imaging spectroscopy data is limited by the traditional classification framework, which carries the requirement of exhaustively defining all classes (species) encountered in a landscape. As the research objective may be to map only one or a few species of interest, we need to explore alternative classification methods that may be used to more efficiently detect a single species. We compared the performance of three support vector machine (SVM) methods designed for single-class detection—binary (one-against-all) SVM, one-class SVM, and biased SVM—in detecting five focal tree and shrub species using data collected by the Carnegie Airborne Observatory over an African savanna. Prior to this comparison, we investigated the effects of training data amount and balance on binary SVM and evaluated alternative methods for tuning one-class and biased SVMs. A key finding was that biased SVM was generally best parameterized by crown-level cross validation paired with the tuning criterion proposed by Lee and Liu [1] . Among the different single-class methods, binary SVM showed the best overall performance (average F-scores 0.43–0.78 among species), whereas one-class SVM showed very poor performance (F-scores 0.09–0.46). However, biased SVM produced results similar to those obtained with binary SVM (F-scores 0.40–0.72), despite using labeled training data from only the focal class. Our results indicate that both binary and biased SVMs can work well for remote single-species detection, while both methods, particularly biased SVM, greatly reduce the amount of training data required compared with traditional multispecies classification.

Conspecific and phylogenetic density‐dependent survival differs across life stages in a tropical forest

Summary Ecologists have long recognized that plant performance is affected by the density and composition of neighbouring individuals. With the advent of highly resolved species‐level phylogenies, it has become possible to test whether such density‐dependent neighbourhood interactions are also phylogenetically dependent. Most studies of density dependence have focused on a single life stage; however, the relative importance of different neighbourhood interactions may shift over the lifetime of an individual. We examined effects of conspecific neighbour density, heterospecific neighbour density and average phylogenetic relatedness of heterospecific neighbours on the survival of seedlings, saplings, juveniles and adult trees of 29 focal tree species using long‐term, spatially explicit forest dynamics data and a highly resolved DNA barcode phylogeny from the tropical forest of Barro Colorado Island (BCI), Panama. Our results show a decline in the strength of conspecific negative density dependence across life stages: strong negative conspecific neighbour effects at early life stages gave way to weak positive conspecific neighbour effects for adult trees. In contrast, the effect of heterospecific neighbour density on survival showed no clear trend with life stage. We found evidence of phylogenetic density dependence in the BCI forest, with a significant negative impact of neighbourhood relatedness on focal tree survival, but only for later life stages. In contrast to studies from other tropical forests, neighbourhood relatedness had a significant positive effect on seedling survival. Furthermore, we found that focal species varied much more widely in their sensitivity to conspecific neighbour density than in their reactions to heterospecific neighbour density or phylogenetic relatedness. Synthesis. Overall, our results demonstrate that both conspecific density dependence and phylogenetic density dependence influence tropical tree survival, but that their relative importance varies with life stage and among species. Our study highlights the need to incorporate multiple life stages and multiple species when assessing the factors contributing to individual survival and species coexistence for long‐lived organisms.

Avian frugivory and seed dispersal of a large fruited tree in an Indian moist deciduous forest

Seed dispersal systems in degraded areas can be compromised following the decline of large-bodied frugivore populations responsible for their dispersal. In this context we examined the seed dispersal ecology of a large fruited deciduous tree (Dillenia pentagyna) along a forest degradation gradient in India. We examined the effect of structural components of vegetation and frugivore foraging behavior on D. pentagyna seed dispersal. Depauperate mammalian community and declined large avian frugivores e.g. hornbills in our study site make this system a specialized one and currently dependent on only two large bodied avian frugivores. Seed dispersal followed an overall leptokurtic pattern and the seed dispersal kernels were best explained by an inverse power function. Seed dispersal kernels in dense forest indicated longer dispersal distances than moderately dense forest and degraded forest. In degraded areas, no dispersal away from the crown was recorded for D. pentagyna and it occurred at low density. Canopy foliage abundance of the surrounding vegetation of the focal trees was best explained by quantity of seed dispersal by large avian frugivores. The number of avian frugivore species those are effective disperser of D. pentagyna decreased along the degradation gradient. Avian frugivore behavior in terms of visitation and seed swallowed is a determining factor that controls quantity of seed dispersal. Our study underscores deleterious impact of forest degradation on avian disperser community which in turn would affect regeneration capacity of degraded forest.

Feeding behavior and aggression in wild Siberut macaques (Macaca siberu) living under low predation risk.

Investigating which factors influence feeding competition is crucial for our understanding of the diversity of social relationships. Socio-ecological models differ in their predictions whether predation risk directly influences feeding competition and which factors exactly predict contest competition. We investigated feeding competition in Siberut macaques (Macaca siberu), a species endemic to Siberut Island (West Sumatra, Indonesia). Siberut macaques experience low predation risk, as major predators (felids, raptors) are absent. They are therefore appropriate subjects to test the prediction that low predation risk reduces feeding competition. To estimate contest potential, we quantified size, spatial distribution and density of food plants, and the availability of alternative resources. We recorded behavior in food patches using a modified focal tree method. Food patches, sorted by decreasing average feeding group size, included large trees (40% of focal plant observations), lianas/strangler (16%), medium trees (9%), small (palm) trees (20%), and rattan (15%). Most food patches were clumped but occurred at low densities relative to the area of average group spread. Thus, availability of alternative food patches was low. Although food patch characteristics indicate high contest potential, the observed aggression rate (0.13 bouts between adults/h) was low relative to other primates. Average feeding group size was small relative to total group size, and feeding group size matched crown volume. Perceived predation risk was low, based on spatial and feeding behavior of juveniles. Together, these results suggest that predation risk may influence feeding competition. Social and temporal factors (patch feeding time), but not ecological factors (fruit abundance in patch and forest, alternative resources) predicted aggression frequency in food patches. Overall, comparative data are still relatively scarce, and researchers should collect more data on group spread, sub-grouping, perceived predation risk, and aggression in food patches before we can draw final conclusions about the role of predation risk for feeding competition.

Multiple-pathway succession in coastal Tsuga heterophylla, Thuja plicata, and Abies amabilis forests on northeastern Vancouver Island, British Columbia

Sustainable forest practices are often designed to mimic natural disturbance and successional processes, yet succession is poorly understood in many ecosystems. On northeastern Vancouver Island, the “disturbance hypothesis” is a widely assumed succession model asserting that shade-tolerant western redcedar (Thuja plicata Donn ex D. Don) and the ericaceous shrub salal (Gaultheria shallon Pursh) invade and colonize highly productive western hemlock (Tsuga heterophylla (Raf.) Sarg.) – Pacific silver fir (Abies amabilis Douglas ex J. Forbes) stands (HA) on zonal sites in the absence of stand-replacing wind disturbance. This leads to the development of low-productivity, low-density, uneven-aged, open-crowned redcedar–hemlock–salal stands (CH). In conflict with this model, old, apparently stable HA stands lacking redcedar can be found on such sites as well. We sought evidence for the predicted transition to CH stands by examining stand composition, crown closure, tree size class frequency distributions, salal cover, and redcedar establishment on young HA (∼90 years old), old HA (>160 years), and CH (>160 years) stands. When adjacent to a redcedar stand, young HA stands had fewer redcedar seedlings but more redcedar adult trees than old HA stands. However, redcedar abundance did not differ between young and old HA stands at distances further than 10 m from adjacent redcedar stands. This could indicate that redcedar recruits into HA stands at stand establishment and that redcedar seedling establishment is low under the thick canopy of young HA stands. The chronosequence data also suggest that both old HA and CH stands are self-replacing stand types in these forests, contrary to the disturbance hypothesis. We develop a new, multipathway model for this ecosystem that is based on the chronosequence data and life-history traits of the focal tree species and suggest that disturbance plays a role opposite to the equilibrium model.

Lluvia de semillas bajo especies de árboles nativos y no-nativos en el Refugio de Vida Silvestre de Cabo Rojo, Puerto Rico

Seed dispersal is a fundamental process in plant ecology and is of critical importance for the restoration of tropical communities. The lands of the Cabo Rojo National Wildlife Refuge (CRNWR), formerly under agriculture, were abandoned in the 1970s and colonized mainly by non-native tree species of degraded pastures. Here we described the seed rain under the most common native and non-native trees in the refuge in an attempt to determine if focal tree geographic origin (native versus non-native) influences seed dispersal. For this, seed rain was sampled for one year under the canopies of four native and four non-native tree species common in this refuge using 40 seed traps. No significant differences were found for the abundance of seeds, or their diversity, dispersing under native versus non-native focal tree species, nor under the different tree species. A significantly different seed species composition was observed reaching native versus non-native focal species. However, this last result could be more easily explained as a function of distance of the closest adults of the two most abundantly dispersed plant species to the seed traps than as a function of the geographic origin of the focal species. We suggest to continue the practice of planting native tree species, not only as a way to restore the community to a condition similar to the original one, but also to reduce the distances needed for effective dispersal.

Trophic cascades in bell miner‐associated dieback forests: Quantifying relationships between leaf quality, psyllids and Psyllaephagus parasitoids

AbstractCoteries of the meliphagid bird Manorina melanophrys are associated with a form of eucalypt defoliation and recovery called bell miner‐associated dieback (BMAD). Through their defence of cooperative colony boundaries against other insectivorous birds, bell miners may foster greater abundances of lerp‐forming psyllids (Hemiptera: Aphalaridae), some of which reduce the lifespan of leaves. Trophic cascades in BMAD forests need to be understood to have a complete picture of regulatory processes. We studied relationships between leaf quality, psyllid and Psyllaephagus parasitoid/hyperparasitoid abundances within the Gondwana Rainforest World Heritage Area, NSW, Australia; our focal tree species were Eucalyptus propinqua and E. biturbinata. Eucalyptus biturbinata had tougher leaves than E. propinqua; leaf toughness of both species varied with site and tree. We found a statistically significant, negative relationship between toughness (surrogate for leaf age) and foliar nitrogen content; younger leaves had higher nitrogen contents. Both bell miner abundance and foliar nitrogen were positively correlated with psyllid abundance. The abundance of Glycaspis species (the psyllid that produces lerps with the highest sugar content) was more closely correlated with foliar nitrogen content than was the abundance of all five psyllid genera combined. We identified 14 Psyllaephagus spp./morphospecies, comprising 11 primary parasitoids and three hyperparasitoids. The abundance of all Psyllaephagus combined was positively correlated with the abundance of lerps. However, psyllid parasitism was not correlated with the abundance of lerps. The abundance of the three hyperparasitoids was positively correlated with the abundance of Psyllaephagus hosts. The availability of epicormic foliage (young, morphologically juvenile leaves produced following defoliation) is likely to alter the nutritional ecology underpinning the diversity and abundance of psyllid populations. Higher quality epicormic foliage should favour populations of Glycaspis species (by enhancing nymphal survival) creating lerp hotspots that induce residency by opportunistic bell miners. The positive contribution of induced amelioration, interacting with feedbacks from parasitoids and hyperparasitoids, to BMAD requires longitudinal investigation.

Competitive balance among tree species altered by forest tent caterpillar defoliation

In northern hardwood forests with a closed canopy, tree growth is largely driven by tree size and competition with neighboring trees. Canopy defoliation during insect outbreaks temporarily increases light availability and may decrease light competition among neighboring trees. Defoliation typically reduces tree growth, but canopy defoliation could also stimulate growth of trees that maintain some leaf area. We compared the growth responses of mature trees of non-host species Acer rubrum, and the three host species Acer saccharum, Quercus rubra and Tilia americana, to defoliation by forest tent caterpillar (Malacosoma disstria, Lasiocampidae), a native forest insect with a ∼10-year outbreak periodicity, in a northern hardwood forest in northern lower Michigan.We compared tree growth during the forest tent caterpillar outbreak in 2009, and in the following year, to the average growth before the outbreak in relation to the defoliation level of both the focal tree and its neighbors. Growth responses were related to focal tree defoliation, but we found little direct evidence for effects of neighborhood defoliation; relatively uniform defoliation within sites may have obscured detection of neighborhood effects. Growth of T.americana increased substantially in the year following defoliation, despite the growth reduction during the outbreak in 2009. T.americana rapidly produced new leaves after peak defoliation in 2009, which could explain increased growth in 2010. A.rubrum, which was not defoliated, decreased growth slightly during the outbreak. In 2010, however, one year after peak defoliation, A. rubrum growth was similar to pre-outbreak growth. The two other defoliated species, A. saccharum and Q. rubra, decreased growth in both 2009 and 2010. These strongly species-specific growth responses to canopy defoliation might result in changes in tree species’ interactions and shifts in species advantages over time.

Serotiny in California Oaks

Although prolonged seed retention, or serotiny, is believed to be an adaptation to highly variable environments such as the Mediterranean regions of California, no prior study has systematically investigated the prevalence of seed retention among California oaks (family Fagaceae), the dominant woody taxon in California foothill woodlands. We quantified the extent to which acorns were retained into and through the winter and spring within the canopy of five species of California oaks at Hastings Reservation, Monterey County. Significant serotiny was found in coast live oak (Quercus agrifolia) and, to a lesser extent, valley oak (Q. lobata), but was absent in blue oak (Q. douglasii), canyon live oak (Q. chrysolepis), and California black oak (Q. kelloggii). In both species where serotiny was observed, seed retention was primarily predicted by the size of the focal tree's acorn crop. In addition, serotiny in coast live oaks was more prevalent in dry years and when the overall acorn crop of coast live oaks was large. We found no evidence that acorn fall in these species is triggered by a specific environmental event. Prolonged seed retention in California oaks renders acorns available in the canopy to wildlife throughout the winter in some years with potentially significant effects extending beyond those of acorn abundance per se.

Trends in bird diversity over 12 years in response to large-scale eucalypt plantation establishment: Implications for extensive carbon plantings

Large-scale plantations established for timber production or for carbon sequestration can dramatically transform landscapes, however little is known about the response of biodiversity. We report on trends in bird diversity during a 12year longitudinal study on three large-scale plantations of locally indigenous eucalypts in northern New South Wales, Australia. The study began in a farmland mosaic and has continued to follow bird occupancy rates after the establishment of eucalypt plantations within the paddock areas. Bird surveys were undertaken at focal trees located in different classes of remnant vegetation, which became embedded within the plantations as well as in the plantation matrix itself. Reference sites were also located in adjacent blocks of forest. We found that species richness increased over time in the plantation matrix, as well as remnant vegetation embedded within the plantation (isolated trees, tree patches and remnants, but not riparian locations). When birds were classified as forest-dependent, forest-associated or mosaic generalist, the species richness of forest-associated birds increased and mosaic generalists decreased over time at selected remnant categories. Richness of forest-dependent birds did not change over time. After plantation establishment, bird composition at remnant locations gradually shifted towards that of forest, although all locations remained distinct from forest even after 11years of plantation growth. The response of 36 individual species was assessed with 47% percent of species increasing over the 11years and 31% of species declining. Notably the noisy miner, a hyper-aggressive species, decreased over time. We suggest a reduction in the occurrence of this species could be an important contributor to the increase in the diversity of smaller bird species. These include species of regional concern, such as the eastern yellow robin and the rufous whistler, which increased over the study period. Our results suggest that large-scale plantations of locally indigenous species contribute to ecological restoration of cleared landscapes. However, the plantation matrix after 11years provided less suitable habitat than nearby forest as it supported fewer species, especially for birds that are characteristic of forest. Retention of remnant vegetation at the time of plantation establishment, including large isolated paddock trees, contributed considerably to the biodiversity present in the plantations and is likely to provide key refuge areas during any subsequent harvesting. Continued collection of longitudinal data are needed to describe changes through the full plantation rotation and harvest, while the extent to which other taxa respond to eucalypt plantation establishment also requires documentation.

Does future climate change facilitate expansion of evergreen broad-leaved tree species in the human-disturbed landscape of the Korean Peninsula? Implication for monitoring design of the impact assessment

To quantitatively assess future change of evergreen broad-leaved tree species' distributions in human-disturbed landscapes of the Korean Peninsula under climate change, potential habitats (PHs) were projected for four important evergreen broad-leaved tree species (Quercus acuta, Castanopsis sieboldii, Machilus thunbergii, and Neolitsea sericea) by species distribution models (SDMs). The distribution data (presence/absence) of the target species in Korea and Japan were used as response variables for SDMs, and climatic data were used as explanatory variables. Three general circulation models under A2 emission scenarios were used as future climate scenarios for the years 2070–2099. Potential habitats masked by land-use data (PHLUs) were projected to assess the impact of anthropogenic activities. Highly accurate SDMs were obtained for all the target species. The current PHs were decreased to 21–35 % by the anthropogenic activities. Future PHLUs for all the target species were projected to increase by 2.0–18.5 times of current PHLUs. These results suggest that all the target species are applicable as indicator species for monitoring in the Korean Peninsula, even if anthropogenic effects are incorporated. Variation of the increasing rate was caused by the differences in the response to temperature changes. M. thunbergii responded sensitively to the increase of minimum temperature of coldest month and had a largest increase in PHLUs under future climate. Therefore, M. thunbergii is considered to be most appropriate species for monitoring the changes of horizontal distributions above all focal evergreen broad-leaved tree species.

Ecological Survey of Avifaunal Resources in University of Port Harcourt, Nigeria

A survey of the avifaunal resources was conducted in the three campuses (Choba, Abuja, and Delta) of the University of Port Harcourt, Nigeria to ascertain their bird species composition, abundance, diversity, and affinity for different tree species. Bird census was carried out on twelve focal trees in each of the three campuses for a period of six months. Shannon-Wiener (H) and Simpson (1 – D) diversity indices were used to measure the diversity of bird species in each of the campuses, while similarity in bird species between campuses was ascertained using Sorensen’s similarity index (SI). Paleontological Statistics (PAST) software was used to obtain a hierarchical classification of the tree species in each campus based on the similarity of bird species sighted on them. A total of 5277 birds belonging to 8 species were encountered in Choba Campus; 3937 belonging to 7 species in Abuja Campus; and 3034 belonging to 8 species in Delta Campus. Choba Campus had the highest bird diversity (H = 0.6623; Simpson 1 – D = 0.3370), followed by Abuja Campus (H = 0.4415; Simpson 1 – D = 0.2217), and Delta Campus (H = 0.1656; Simpson 1 – D = 0.05804). Similarity in bird species composition was highest between Abuja Campus and Delta Campus (SI = 93%) and least between Choba Campus and Delta Campus (SI = 63%). Ploceus cucullatus was the most abundant bird species in the three campuses. In Abuja Campus, Cocus nucifera, Polyalthia longifolia and Terminalia catappa were ecologically the most distant tree species with respect to bird species composition; in Delta Campus, Cocus nucifera, Pinus caribaea, and Polyalthia longifolia, were the most ecologically distant; while Hura crepitans and Polyalthia longifolia were the most ecologically distant in Choba Park. Further investigation is required to ascertain why bird species in the various campuses showed no affinity for Cocus nucifera and Polyalthia longifolia.Key words: University of Port Harcourt, avifauna, abundance, diversity, tree-bird interaction

Flowering phenology and its implications for management of big‐leaf mahogany Swietenia macrophylla in Brazilian Amazonia

Flowering phenology is a crucial determinant of reproductive success and offspring genetic diversity in plants. We measure the flowering phenology of big-leaf mahogany (Swietenia macrophylla, Meliaceae), a widely distributed neotropical tree, and explore how disturbance from logging impacts its reproductive biology. We use a crown scoring system to estimate the timing and duration of population-level flowering at three forest sites in the Brazilian Amazon over a five-year period. We combine this information with data on population structure and spatial distribution to consider the implications of logging for population flowering patterns and reproductive success. Mahogany trees as small as 14 cm diam flowered, but only trees > 30 cm diam flowered annually or supra-annually. Mean observed flowering periods by focal trees ranged from 18-34 d, and trees flowered sequentially during 3-4 mo beginning in the dry season. Focal trees demonstrated significant interannual correlation in flowering order. Estimated population-level flowering schedules resembled that of the focal trees, with temporal isolation between early and late flowering trees. At the principal study site, conventional logging practices eliminated 87% of mahogany trees > 30 cm diam and an estimated 94% of annual pre-logging floral effort. Consistent interannual patterns of sequential flowering among trees create incompletely isolated subpopulations, constraining pollen flow. After harvests, surviving subcommercial trees will have fewer, more distant, and smaller potential partners, with probable consequences for post-logging regeneration. These results have important implications for the sustainability of harvesting systems for tropical timber species.

2013 Biotropica Award for Excellence in Tropical Biology and Conservation

THE ASSOCIATION FOR TROPICAL BIOLOGY AND CONSERVATION and the Editors of Biotropica proudly announce the winner of the 2013 Biotropica Award for Excellence in Tropical Biology and Conservation, presented to the author of a paper published in Biotropica during 2012. We recognize an outstanding contribution based on original research conducted in tropical regions. Criteria include clarity of presentation, strong basis in natural history, well-planned experimental and/or sampling design, and novel insights gained into critical processes that influence the structure and functioning of tropical biological systems. The 2013 Award is presented to Jordan Karubian, Renata Dur~aes, Jenny L. Storey and Thomas B. Smith for their paper entitled ‘Mating Behavior Drives Seed Dispersal by the Long-wattled Umbrellabird Cephalopterus penduliger’ published in Biotropica 44(5): 689– 698. Seed dispersal is a critical process shaping many terrestrial ecosystems. Seed dispersal by animals (zoochory) has long attracted the attention of tropical biologists, not least because of the preponderance of tree species in moist tropical forests producing fleshy fruit for animal dispersal. The fascinating mutualisms which have evolved between plants and their animal disperses, and the potential for disruption of these mutualisms— particularly by habitat fragmentation and other human disturbances—present both a fascinating and highly applied field of research. Zoochory is a driving force in forest tree community structure, forest recovery following disturbance, and management of tropical forests. Despite this importance, few studies have effectively evaluated seed dispersal with adequate consideration of both the behavior of the animal dispersal agent and implication for plant species recruitment. Karubian and colleagues address this issue by a very wellconceived study applying novel field techniques (GIS and radio telemetry), traditional ecological approaches (gut retention time), and a solid foundation in natural history to investigate the importance of disperser behavior for seed dispersal in a biodiversity hotspot – the Choc!o rain forests of Northwest Ecuador and West Colombia. Their considerable body of ecological data enabled them to demonstrate the importance of mating behavior (lekking) in shaping seed dispersal and its potential importance for forest community structure. Karubian et al. focus on the charismatic and endemic Longwattled Umbrellabird, which is one of the few large avian frugivores in the Choc!o. Their study reveals that territorial male Umbrellabirds, which congregate in leks, spend a considerable proportion of their time defending small display areas. In contrast, females are solitary and only visit the leks to mate. Using detailed movement and home range data from individual birds and corresponding gut retention times for seeds from different tree species, Karubian et al. elegantly reveal spatially explicit probabilities of seed dispersal—differences in behaviour between males, females, and non-territorial’floater’ males have important implications for seed dispersal. Furthermore, the inclusion of an empirical validation of dispersal patterns by spatial analyses of the density of seed, seedlings, and adults of five forest tree species shows how behavior drives the high density of seedlings around leks. This excellent contribution advances our mechanistic understand of how bird behavior can be important in shaping seed dispersal patterns. It also paves the way for novel studies to explore long-standing questions of tree species coexistence, such as the Janzen-Connell hypothesis. In combination with earlier molecular analysis of one of the five focal tree species (the palm Oenocarpus bataua), Karubian et al., highlight the value of combining multiple empirical approaches in a single study to unravel this cryptic yet critical ecological process.

Effects of plant phylogenetic diversity on herbivory depend on herbivore specialization

Summary Pest regulation is an important ecosystem service provided by biodiversity, as plants growing in species‐rich communities often experience associational resistance to herbivores. However, little is known about the respective influence of the quantity and identity of associated species on herbivory in focal plants. Using a meta‐analysis to compare insect herbivory in pure and mixed forests, we specifically tested the effects of the relative abundance of focal tree species and of phylogenetic distance between focal and associated tree species on the magnitude of associational resistance. Overall, insect herbivory was significantly lower in mixed forests, but the outcome varied greatly depending on the phylogenetic relatedness among tree species and the degree of herbivore feeding specialization. Specialist herbivore damage or abundance was positively related to relative abundance of their host trees, regardless of the phylogenetic distance between host and associated tree species. By contrast, tree diversity triggered associational resistance to generalist herbivores only when tree mixtures included tree species phylogenetically distant to the focal species. Synthesis and applications. Our study demonstrates that the establishment of mixed forests per se is not sufficient to convey associational resistance to herbivores if the identity of tree species associated in mixtures is not taken into account. As a general rule, mixing phylogenetically more distinct tree species, such as mixtures of conifers and broadleaved trees, results in more effective reduction in herbivore damage.