Forest Edges as Nutrient and Pollutant Concentrators: Potential Synergisms between Fragmentation, Forest Canopies, and the Atmosphere

Abstract: Forest fragmentation leads to a dramatic increase in forest edge, and these edges may function as traps and concentrators for wind-borne nutrients and pollutants. We assessed the influence of forest edges on atmospheric deposition and subsequent inputs to the forest floor in deciduous-forest fragments in the eastern United States. To quantify these inputs, we collected throughfall—water that has passed through the forest canopy—from edge and interior zones of forests adjacent to open fields. During the 1995 growing season, atmospheric input (wet and dry deposition) of sulfur to forest edge zones was elevated compared with input to forest interiors. Throughfall fluxes of dissolved inorganic nitrogen and calcium were also greater at edges than interiors. The mean edge increases ranged from 17% to 56% for the nutrients and pollutants we measured. When we manipulated the structure of forest edges by removing all vegetation below half the canopy height, throughfall flux in the edge zone declined sharply and was less than that of the respective interior zone. Changing the vegetation structure of the edge also shifted the zone of highest throughfall flux farther into the interior of the forest. Our data suggest that forest edges can function both as significant traps for airborne nutrients and pollutants from adjoining agricultural or urban landscapes and effective concentrators of below-canopy chemical fluxes. These enhanced fluxes may have cascading effects on soil-nutrient cycling, microbial activity, seedling dominance, and other ecological processes near forest edges.     

Design and validation of a spatially explicit simulation model for bottomland hardwood forests

Species composition in forests depends on the interaction of species traits and species availability. Yet many forest simulation models focus only on interactions of adult trees and saplings, ignoring how species become members of the community. We modify a published forest model for bottomland hardwood forests (program SWAMP [Phipps, R.L., 1979. Simulation of wetlands forest vegetation dynamics. Ecol. Modell. 7, 257–288]) to make it spatially explicit and incorporate explicit seed production and dispersal algorithms. The resulting individual-based, spatially explicit forest simulator (YAFSIM) combines mechanistic seed dispersal with growth and mortality of trees to track forest dynamics over time. We describe the structure of the model and test its validity for dynamics in small bottomland hardwood patches in the Mississippi Alluvial Valley. Dynamics of species composition and basal areas of trees predicted by Yazoo Forest Simulator (YAFSIM) were similar to those of natural second- and old-growth bottomland forests. However, diversity of simulated forest patches declined over time largely because of random dynamics acting on small, isolated populations.     

Introduced Birds and the Fate of Hawaiian Rainforests

Abstract:  The Hawaiian Islands have lost nearly all their native seed dispersers, but have gained many frugivorous birds and fleshy-fruited plants through introductions. Introduced birds may not only aid invasions of exotic plants but also may be the sole dispersers of native plants. We assessed seed dispersal at the ecotone between native- and exotic-dominated forests and quantified bird diets, seed rain from defecated seeds, and plant distributions. Introduced birds were the primary dispersers of native seeds into exotic-dominated forests, which may have enabled six native understory plant species to become reestablished. Some native plant species are now as common in exotic forest understory as they are in native forest. Introduced birds also dispersed seeds of two exotic plants into native forest, but dispersal was localized or establishment minimal. Seed rain of bird-dispersed seeds was extensive in both forests, totaling 724 seeds of 9 native species and 2 exotics with over 85% of the seeds coming from native plants. Without suitable native dispersers, most common understory plants in Hawaiian rainforests now depend on introduced birds for dispersal, and these introduced species may actually facilitate perpetuation, and perhaps in some cases restoration, of native forests. We emphasize, however, that restoration of native forests by seed dispersal from introduced birds, as seen in this study, depends on the existence of native forests to provide a source of seeds and protection from the effects of ungulates. Our results further suggest that aggressive control of patches of non-native plants within otherwise native-dominated forests may be an important and effective conservation strategy.     

Incorporating animal behavior into seed dispersal models: implications for seed shadows

Seed dispersal fundamentally influences plant population and community dynamics but is difficult to quantify directly. Consequently, models are frequently used to describe the seed shadow (the seed deposition pattern of a plant population). For vertebrate-dispersed plants, animal behavior is known to influence seed shadows but is poorly integrated in seed dispersal models. Here, we illustrate a modeling approach that incorporates animal behavior and develop a stochastic, spatially explicit simulation model that predicts the seed shadow for a primate-dispersed tree species (Virola calophylla, Myristicaceae) at the forest stand scale. The model was parameterized from field-collected data on fruit production and seed dispersal, behaviors and movement patterns of the key disperser, the spider monkey (Ateles paniscus), densities of dispersed and non-dispersed seeds, and direct estimates of seed dispersal distances. Our model demonstrated that the spatial scale of dispersal for this V. calophylla population was large, as spider monkeys routinely dispersed seeds >100 m, a commonly used threshold for long-distance dispersal. The simulated seed shadow was heterogeneous, with high spatial variance in seed density resulting largely from behaviors and movement patterns of spider monkeys that aggregated seeds (dispersal at their sleeping sites) and that scattered seeds (dispersal during diurnal foraging and resting). The single-distribution dispersal kernels frequently used to model dispersal substantially underestimated this variance and poorly fit the simulated seed-dispersal curve, primarily because of its multimodality, and a mixture distribution always fit the simulated dispersal curve better. Both seed shadow heterogeneity and dispersal curve multimodality arose directly from these different dispersal processes generated by spider monkeys. Compared to models that did not account for disperser behavior, our modeling approach improved prediction of the seed shadow of this V. calophylla population. An important function of seed dispersal models is to use the seed shadows they predict to estimate components of plant demography, particularly seedling population dynamics and distributions. Our model demonstrated that improved seed shadow prediction for animal-dispersed plants can be accomplished by incorporating spatially explicit information on disperser behavior and movements, using scales large enough to capture routine long-distance dispersal, and using dispersal kernels, such as mixture distributions, that account for spatially aggregated dispersal.     

Vegetation Responses along Edge-to-Interior Gradients in the Mixed Hardwood Forests of the Roanoke River Basin, North Carolina

Compared with forest interiors, forest edges typically have a different plant species composition and community structure, a phenomenon known as "edge effect." Edge effects make the functional interior area of a forest smaller than its actual area. The objective of this study was to estimate how far the effects of agriculturally maintained edges penetrate the mixed hardwood forests of the Roanoke River Basin, North Carolina. I determined percentage cover for all vascular plant species in 10-by-100-meter belt transects on north-facing or south-facing edges of four relatively undisturbed forests. Changes in the percentage cover of individual species, the relative cover of exotic species, and species richness all indicated that edge effects penetrate deeper on south-facing edges (to 60 meters) than on north-facing edges (to 20 meters). Analyses of species responses to the edge showed a number of species to be edge oriented, but no species was found to be interior oriented. The results of multivariate analyses (ordination and cluster analysis) suggested that edge effects could be detected to 50 meters on south-facing edges and 10–30 meters on north-facing edges. These results allow us to better understand the difference between a forest's actual area and its functional interior area.     

The importance of seed dispersal in the Alexandria Coastal Dunefield, South Africa

The endozoochorous dispersal of seeds by mammals and birds between distinct vegetation communities was assessed to determine the importance of these processes in coastal dune field management. Isolated pockets of thicket vegetation (bush-pockets) within a large coastal dune field provided the opportunity to study vertebrate seed dispersal and its contribution to their origin and maintenance. Mammalian and avian faeces were collected for the quantification of seeds dispersed via endozoochory. Birds and mammals showed considerable overlap, dispersing intact seeds of 17 and 29 plant species, respectively, but mammals dispersed a greater diversity and size range than birds. Extrapolation of mammalian faecal data indicates an annual input of 23 million intact seeds to the dune field. Significantly more seeds are deposited by mammals and birds in the bush-pockets than on open sand, and birds deposited greater numbers of seeds nearer the seed source. Zoochory appears to be critical for the maintenance of the bush-pocket habitats through the dispersal of climax woody plant species into the dune field. Directional dispersal by birds and mammals to the bush-pockets is considered to be responsible for the maintenance and possible origin of these bush-pockets. The high number of exotic plant propagules dispersed by both avian and mammalian zoochory highlights the importance of management of the Alexandria Coastal Dunefield (ACD) beyond the reserve boundaries. In a dynamic system such as the ACD which is within a declared nature reserve, the continued existence of the bush-pockets may depend on the maintenance, beyond the reserve boundaries, of a reservoir of not only plant material but vertebrate dispersers as well.     

Effects of Pioneer Tree Species Hyperabundance on Forest Fragments in Northeastern Brazil

Abstract: Despite many studies on fragmentation of tropical forests, the extent to which plant and animal communities are altered in small, isolated forest fragments remains obscure if not controversial. We examined the hypothesis that fragmentation alters the relative abundance of tree species with different vegetative and reproductive traits. In a fragmented landscape (670 km²) of the Atlantic Forest of northeastern Brazil, we categorized 4056 trees of 182 species by leafing pattern, reproductive phenology, and morphology of seeds and fruit. We calculated relative abundance of traits in 50 1‐ha plots in three types of forest configurations: forest edges, small forest fragments (3.4–83.6 ha), and interior of the largest forest fragment (3500 ha, old growth). Although evergreen species were the most abundant across all configurations, forest edges and small fragments had more deciduous and semideciduous species than interior forest. Edges lacked supra‐annual flowering and fruiting species and had more species and stems with drupes and small seeds than small forest fragments and forest interior areas. In an ordination of species similarity and life‐history traits, the three types of configurations formed clearly segregated clusters. Furthermore, the differences in the taxonomic and functional (i.e., trait‐based) composition of tree assemblages we documented were driven primarily by the higher abundance of pioneer species in the forest edge and small forest fragments. Our work provides strong evidence that long‐term transitions in phenology and seed and fruit morphology of tree functional groups are occurring in fragmented tropical forests. Our results also suggest that edge‐induced shifts in tree assemblages of tropical forests can be larger than previously documented.     

Spatial and temporal patterns of seed dispersal: an important determinant of grassland invasion.

We measured spatial and temporal patterns of seed dispersal and seedling recruitment for 58 species in a grassland community to test whether seed dispersal could predict patterns of invasion after disturbance. For the 12 most abundant grasses, recruitment of native species was dependent on the propagule supply of both native and exotic species. Variability in seed rain on small spatial (1-10 m) and temporal (within season) scales led to qualitative differences in the outcome of disturbance colonization such that native species dominated disturbances when exotic seed supply was low but failed to establish when exotic seed supply was high. Local dispersal and spatial heterogeneity in species composition promoted coexistence of native and exotic species by creating refuges from high exotic seed supply within native dominated patches. Despite this, copious exotic seed production strongly limited recruitment of native species in exotic dominated patches. Most grasslands in California are presently dominated by exotic species, suggesting that competition at the seedling stage is a major barrier to native species restoration.     

森林土壤种子库研究进展

土壤种子库与物种多样性存在密切相关性,森林土壤种子库是植被天然更新的物质基础。文章阐述了森林土壤种子库的内涵、森林生态系统土壤种子库的基本特征及其主要研究方法,探讨了影响种子库的基本因素及当前极为关注的热点问题。在受损森林生态系统目标树种培养、植被群落快速恢复和生态系统科学管理等领域仍存在一些理论和实践急待解决的问题,如随着群落进展演替土壤种子库种子数量在增加而质量却在逐渐下降,面临如何解决生态系统健康稳定发育和物种多样性长期维持问题。文章认为今后应加强土壤种子库与生物多样性保护、防止外来物种入侵乡土物种利用及对全球变化的响应等领域的研究工作,以期为从事森林土壤种子库研究和退化森林植被群落恢复实践提供理论指导。     

Distribution of Carabid Beetles (Coleoptera, Carabidae) across a Boreal Forest–Clearcut Ecotone

Abstract: We studied the occurrence of carabid beetles (Coleoptera, Carabidae) in boreal forest fragments, their edges, and adjacent clearcuts in central Finland. Beetles were collected with pitfall traps along transects extending 60 m from the edge into clearcuts and 60 m into forest interior. Our main findings were that (1) species richness was significantly higher in the clearcut than in the forest fragments, (2) clearcuts hosted many open-habitat species, which increased overall species richness in these sites, (3) carabid assemblages in the edges were more similar to forest assemblages than to those found in the clearcuts, (4) no edge specialists were found, and (5) open-habitat species did not penetrate into the forest fragments from the clearcut. Because forest specialists occurred all the way to the edge on the forest side, it seems that edge effects per se do not adversely affect these species, at least in the short term. In the long term, however, habitat conditions in the edges may deteriorate for interior species because of trees falling over in strong winds, thereby reducing the size of the fragments and widening the edge zone.     

Meta‐Analysis of the Effects of Human Disturbance on Seed Dispersal by Animals

Animal‐mediated seed dispersal is important for sustaining biological diversity in forest ecosystems, particularly in the tropics. Forest fragmentation, hunting, and selective logging modify forests in myriad ways and their effects on animal‐mediated seed dispersal have been examined in many case studies. However, the overall effects of different types of human disturbance on animal‐mediated seed dispersal are still unknown. We identified 35 articles that provided 83 comparisons of animal‐mediated seed dispersal between disturbed and undisturbed forests; all comparisons except one were conducted in tropical or subtropical ecosystems. We assessed the effects of forest fragmentation, hunting, and selective logging on seed dispersal of fleshy‐fruited tree species. We carried out a meta‐analysis to test whether forest fragmentation, hunting, and selective logging affected 3 components of animal‐mediated seed dispersal: frugivore visitation rate, number of seeds removed, and distance of seed dispersal. Forest fragmentation, hunting, and selective logging did not affect visitation rate and were marginally associated with a reduction in seed‐dispersal distance. Hunting and selective logging, but not fragmentation, were associated with a large reduction in the number of seeds removed. Fewer seeds of large‐seeded than of small‐seeded tree species were removed in hunted or selectively logged forests. A plausible explanation for the consistently negative effects of hunting and selective logging on large‐seeded plant species is that large frugivores, as the predominant seed dispersers for large‐seeded plant species, are the first animals to be extirpated from hunted or logged forests. The reduction in forest area after fragmentation appeared to have weaker effects on frugivore communities and animal‐mediated seed dispersal than hunting and selective logging. The differential effects of hunting and selective logging on large‐ and small‐seeded tree species underpinned case studies that showed disrupted plant‐frugivore interactions could trigger a homogenization of seed traits in tree communities in hunted or logged tropical forests. Meta Análisis de los Efectos de la Perturbación Humana sobre la Dispersión de Semillas por Animales     

Edge Effects on the Understory Bird Community in a Logged Forest in Uganda

Abstract: Understanding how the fauna of logged tropical rainforests responds to fragmentation and the creation of edges is vital to ensure conservation of biodiversity. We studied the composition of the understory bird community from the edge of a 15-ha clearing toward the interior of the forest in a part of Budongo Forest Reserve, Uganda, that was selectively logged about 45 years ago. Mist netting was conducted along five transects from the edge and 500 m into the interior. The total number of individuals captured did not change with distance from the edge, but there was a significant increase in the number of species. We sampled fewer, but more common species near the edge, whereas the interior of the forest had more, and less common species. Guild composition also changed with distance from the edge. Frugivore-insectivores and nectarivores were most common close to the edge. Among insectivores, ground foragers, bark-gleaners, and leaf-gleaners were most common in the interior of the forest, whereas sallying insectivores favored the edge. Graminivores were unaffected by the edge. Analysis of common species showed that Ispidina picta , Andropadus curvirostris , A. latirostris , Camaroptera brachyura , Terpsiphone rufiventer , and Nectarinia olivacea were associated with the edge, but no species showed significant avoidance of the edge. This finding may be explained by the generally low sample sizes of interior species. Our results show that even bird communities in logged forests respond to edges. Estimates of edge effects suggested that changes in bird densities may have occurred several hundred meters from the edge. In conclusion, logged forests provide habitat for bird species avoiding forest edges, and this should be considered in the management of such forests for conservation.     

Plant-Mammal Interactions in Tropical Bolivian Forests with Different Hunting Pressures

Abstract: We studied plant-animal interactions and vegetation structure in two geographically close tropical Bolivian forests subjected to different hunting intensities. We hypothesized that reduction of mammals openface> 1 kg in an "intensively hunted forest," compared with an "occasionally hunted forest," should correlate with decreased seed predation and seedling trampling, increased seedling survival and density, and decreased tree-species diversity at the seedling stage in relation to the adult stage. The occasionally hunted forest held 1.7 times as many mammalian species as the intensively hunted forest. As predicted, predation of Astrocaryum murumuru seeds was 34.2% lower in the intensively hunted forest. Similarly, trampling of model seedlings was 5.4 times lower and seedling survival was 1.15 times greater in the intensively hunted forest than that in the occasionally hunted forest. But the intensively hunted forest displayed lower seedling densities and a higher ratio of seedling diversity to tree diversity than did the occasionally hunted forest. Reduction of peccaries from the intensively hunted forest may explain much of the between-site differences in seed predation, trampling, and seedling survival. Lack of consistent differences in seedling density and diversity could mean that reduced granivory and trampling may be counteracted by reduced seed dispersal. The reduction of mammalian populations may produce a complex mosaic of forest patches with distinct degrees of structural change, depending on the intensity of defaunation.     

A Natural Experiment on the Impact of Overabundant Deer on Forest Invertebrates

Abstract:  In large parts of North America and Europe, deer overabundance threatens forest plant diversity. Few researchers have examined its effects on invertebrate assemblages. In a natural experiment on Haida Gwaii (British Columbia, Canada), where Sitka black-tailed deer ( Odocoileus hemionus sitkensis ) were introduced, we compared islands with no deer, with deer for fewer than 20 years, and with deer for more than 50 years. We sampled invertebrates in three habitat categories: forest edge vegetation below the browse line, forest interior vegetation below the browse line, and forest interior litter. In forest edge vegetation, invertebrate abundance and species density decreased with increasing length of browsing history. In forest interior vegetation, decrease was significant only on islands with more than 50 years of browsing. Insect abundance in the vegetation decreased eightfold and species density sixfold on islands browsed for more than 50 years compared with islands without deer. Primary consumers were most affected. Invertebrates from the litter showed little or no variation related to browsing history. We attributed the difference between vegetation-dwelling and litter-dwelling invertebrates to differences in the effect of browsing on their habitat. In the layer below the browse line deer progressively removed the habitat. The extent of litter habitat was not affected, but its quality changed. We recommend more attention be given to the effect of overabundant ungulates on forest invertebrate conservation with a focus on edge and understory vegetation in addition to litter habitat.     

Edge Effects on Lizards and Frogs in Tropical Forest Fragments

Abstract: We investigated whether forest-pasture edges affect the distribution of an assemblage of small vertebrate ectotherms in a consistent and predictable manner. We describe the abundance and distribution of two species of anoline lizards (   Norops ) and five species of leaf-litter frogs (   Eleutherodactylus ) along the edges and in the interiors of nine forest fragments near Las Cruces, Costa Rica. Over 4 months, we surveyed 44 pairs of plots by visual encounter. In each pair of plots, one was immediately adjacent to the pasture and the second was within the forest "interior." Both plots of a pair were searched simultaneously. This block design controlled for the effects of weather, topography, and searcher ability. The distribution of all species was highly variable with respect to edges. Only two species of frogs, Eleutherodactylus podiciferus and E. cruentus , were significantly more abundant in interior plots than in edge plots, although not consistently so. Both species of Norops lizards were more abundant along forest edges during the dry season. Both Norops species and several Eleutherodactylus species, however, appeared to become more abundant in the forest interior after the onset of the wet season, suggesting a seasonal edge effect. In Norops polylepis , the most abundant anole, rates of ectoparasitism were lower along edges than in forest interiors. The magnitude of the edge effect on any one species was not influenced by the size of fragments or by the distance of the interior plot from the nearest edge. We believe that edge effects should not be defined by the distance to which they are detected. Rather, they should be viewed as highly dynamic in space and time; taxa appear to respond to different components of edge effects according to their particular biological requirements.     

Hunting Increases Dispersal Limitation in the Tree Carapa procera, a Nontimber Forest Product

Abstract:  The sustainability of seed extraction from natural populations has been questioned recently. Increased recruitment failure under intense seed harvesting suggests that seed extraction intensifies source limitation. Nevertheless, areas where more seeds are collected tend to also have more intense hunting of seed-dispersing animals. We studied whether such hunting, by limiting disperser activity, could cause quantitative dispersal limitation, especially for large crops and for crops in years of high seed abundance. In each of four Carapa procera (Meliaceae) populations in French Guiana and Surinam, two with hunting and two without, we compared seed fate for individual trees varying in crop size in years of high and low population-level seed abundance. Carapa seeds are a nontimber forest product and depend on dispersal by scatter-hoarding rodents for survival and seedling establishment. Hunting negatively affected the proportion of seeds dispersed and caused greater numbers of seeds to germinate or be infested by moths below parent trees, where they would likely die. Hunting of seed-dispersing animals disproportionally affected large seed crops, but we found no additional effect of population-level seed abundance on dispersal rates. Consistently lower rates of seed dispersal, especially for large seed crops, may translate to lower levels of seedling recruitment under hunting. Our results therefore suggest that the subsistence hunting that usually accompanies seed collection is at the cost of seed dispersal and may contribute to recruitment failure of these nontimber forest products. Seed extraction from natural populations may affect seedling recruitment less if accompanied by measures adequately incorporating and protecting seed dispersers.     

Meta‐Analysis of the Effects of Forest Fragmentation on Interspecific Interactions

Forest fragmentation dramatically alters species persistence and distribution and affects many ecological interactions among species. Recent studies suggest that mutualisms, such as pollination and seed dispersal, are more sensitive to the negative effects of forest fragmentation than antagonisms, such as predation or herbivory. We applied meta‐analytical techniques to evaluate this hypothesis and quantified the relative contributions of different components of the fragmentation process (decreases in fragment size, edge effects, increased isolation, and habitat degradation) to the overall effect. The effects of fragmentation on mutualisms were primarily driven by habitat degradation, edge effects, and fragment isolation, and, as predicted, they were consistently more negative on mutualisms than on antagonisms. For the most studied interaction type, seed dispersal, only certain components of fragmentation had significant (edge effects) or marginally significant (fragment size) effects. Seed size modulated the effect of fragmentation: species with large seeds showed stronger negative impacts of fragmentation via reduced dispersal rates. Our results reveal that different components of the habitat fragmentation process have varying impacts on key mutualisms. We also conclude that antagonistic interactions have been understudied in fragmented landscapes, most of the research has concentrated on particular types of mutualistic interactions such as seed dispersal, and that available studies of interspecific interactions have a strong geographical bias (arising mostly from studies carried out in Brazil, Chile, and the United States). Meta‐Análisis de los Efectos de la Fragmentación del Bosque sobre las Interacciones Interespecíficas     

Edge effects on trophic cascades in tropical rainforests

The cascading effects of biodiversity loss on ecosystem functioning of forests have become more apparent. However, how edge effects shape these processes has yet to be established. We assessed how edge effects alter arthropod populations and the strength of any resultant trophic cascades on herbivory rate in tropical forests of Brazil. We established 7 paired forest edge and interior sites. Each site had a vertebrate-exclosure, procedural (exclosure framework with open walls), and control plot (total 42 plots). Forest patches were surrounded by pasture. Understory arthropods and leaf damage were sampled every 4 weeks for 11 months. We used path analysis to determine the strength of trophic cascades in the interior and edge sites. In forest interior exclosures, abundance of predaceous and herbivorous arthropods increased by 326% and 180%, respectively, compared with control plots, and there were significant cascading effects on herbivory. Edge-dwelling invertebrates responded weakly to exclusion and there was no evidence of trophic cascade. Our results suggest that the vertebrate community at forest edges controls invertebrate densities to a lesser extent than it does in the interior. Edge areas can support vertebrate communities with a smaller contingent of insectivores. This allows arthropods to flourish and indirectly accounts for higher levels of plant damage at these sites. Increased herbivory rates may have important consequences for floristic community composition and primary productivity, as well as cascading effects on nutrient cycling. By interspersing natural forest patches with agroforests, instead of pasture, abiotic edge effects can be softened and prevented from penetrating deep into the forest. This would ensure a greater proportion of forest remains habitable for sensitive species and could help retain ecosystem functions in edge zones.     

Effects of Roads on Movements by Understory Birds in Mixed-Species Flocks in Central Amazonian Brazil

Abstract: Roads through tropical forest create linear disturbances that have unknown consequences for forest birds. We studied how a narrow, rarely used road through otherwise undisturbed Amazonian forest affected the movements and area requirements of understory birds that form mixed-species flocks. Differences in road maintenance led to two distinct treatments along the same road. Trees along the "closed" road formed a partial canopy connecting the two sides of the road, although the roadway itself was kept open. The "open" road was regularly maintained, making a complete opening 10–30 m wide.We followed 15 flocks, 5 each in interior forest, along the open road, and along the closed road. These flocks were led by Thamnomanes antshrikes, and each flock had a discreet, permanent territory. Flock territory size (mean = 8.5 ha) did not differ among the three locations. The open road formed the territorial boundary for all five flocks, although birds moved within a few meters of the edge of the road. The closed road was less of a barrier: 2 of 5 flocks used both sides of the closed road. Playback experiments showed that flocks readily crossed the closed road to approach agonistic vocalizations. Along the open road, even though birds responded to playback by becoming agitated and moving to the extreme edge of the roadside vegetation, they were less likely to cross the road and did so only after a longer duration of playback. Our results suggest that flocks respond to a road as they would to a long linear gap. They use the vegetation along the edges of the road, but because they are unwilling to cross the open area, it becomes a flock territory boundary. Similarly, as in forest gaps, successional change along the closed road produced suitable habitat for flocks. Although this suggests that roads are a trivial problem, we caution that this result applies only to narrow roads that are not accompanied by deforestation or other disturbance.     

Sequential sampling designs for catching the tail of dispersal kernels

Methods to design a sampling strategy should depend on the research question involved when conducting the experiment. The objective of this study is to design a seed trap configuration surrounding a parent plant when the long distance component of the seed dispersal kernel is of interest. In particular, as a population’s invasion speed depends mainly on the tail of the dispersal kernel, the sampling design in this study is based on calculating this quantity. The optimality criterion is to minimize the mean squared error (MSE) of the estimated invasion speed (using a limited number of traps) with respect to the “true” calculated invasion speed. Detailed procedures are given on how to calculate an invasion speed, both in a 1D and a 2D setting, with examples on how to implement the method to get a local optimal sampling strategy using Calluna vulgaris as a test system. Results show a trade-off between nearby sampling (many seeds, no long-distance dispersal measured) and distant sampling (few seeds, but long-distance dispersal measured).