Consequences of tropical dry forest conversion on diaspore fate of Enterolobium contortisiliquum (Fabaceae)

Habitat conversion is one of the major threats for biodiversity conservation and viability of natural populations. Thus, habitat disturbance alters distinct ecological processes, such as plant reproductive success and diaspore fate. In this study, we determined the effects of seasonally tropical dry forests (STDFs) conversion by anthropogenic disturbance by assessing diaspore fate of Enterolobium contortisiliquum. We compared 20 adult trees present in a STDFs preserved area and 20 adult trees present in a human-converted area. In general, diaspore fates from both areas were similar, i.e., there was no difference in the reproductive success of trees in STDFs and human-converted area. Habitat disturbance did not affect the length or width of fruits; only fruit thickness was larger in trees of STDFs habitat. None of the biometric seed measures differed between different habitat conditions. Likewise, the number of undamaged seeds, aborted seeds, pre-dispersal predated seeds, and seed production were independent of habitat conditions. Besides, we did not observe any effect of habitat disturbance on germination percentage. However, seeds from preserved STDFs germinated faster than seeds from the human-converted area. Even though the effects of human-modified habitats on the diaspore fate have already been studied, tree species exhibit different responses to habitat conversion regarding seed predation, seed dispersal, seed germination, and seedling establishment. Overall, our results show that habitat disturbance does not affect the diaspore fate of E. contortisiliquum. This study also highlights the importance of remnants trees in converted landscapes as the population’s connectors which maintain plant–animal mutualistic and antagonistic interactions that mitigate the effects of habitat disturbance.

     

半附生榕树和非附生榕树的细根性状

榕树作为热带雨林生态系统中的一个关键类群,在维持生物多样性方面发挥着重要作用。本研究以中国科学院西双版纳热带植物园内的榕树专类园区的10种榕属树种(5种半附生,5种非附生)为对象,采用根序法对其细根直径、根长、比根长、比表面积、分枝密度、组织密度、氮含量、碳含量和碳氮比等9个细根功能性状进行了研究,分析了半附生榕树和非附生榕树的细根性状差异;同时结合其原始分布生境,从植物的细根形态功能性状角度阐释其生存策略。结果表明:半附生榕的细根根长、细根直径显著高于非附生榕树(P!0.01),而其比根长和分枝密度显著低于非附生榕树,其余性状之间无显著差异(P>0.05); 10种榕树的细根形态特征与养分特征呈微弱或无相关关系,细根的直径与分枝密度、比根长和比表面积呈显著的负相关。研究认为,不同生活型榕树的根系结构和性状特征差异是对环境的适应表现,分布于山脊干旱环境的半附生榕树细根具有直径较粗、根系长、分枝密度和比根长低的特性,使其具有较好的水分吸收能力,并可能与菌根真菌有更紧密的互利共生关系,从而能适应相对干旱的山脊环境。     

Effects of habitat disruption on the activity of nectarivorous bats (Chiroptera: Phyllostomidae) in a dry tropical forest: implications for the reproductive success of the neotropical tree Ceiba grandiflora

In the tropical dry forest of the central Pacific coast of Mexico the pollination and reproductive success of the bombacaceous tree Ceiba grandiflora was negatively affected by habitat disruption. Two of the three bat species that function as effective pollinators for this species ( Glossophaga soricina and Musonycteris harrisoni) visited flowers found in trees in disturbed habitats significantly less than trees found in undisturbed habitats. A similar pattern was observed for the effective bat pollinator, Leptonycteris curasoae; however the difference was not significant. The three nectarivorous bats that functioned as effective pollinators of C. grandiflora also visited flowers to exclusively feed on pollen by biting or pulling off an anther (see Fig. S1 of Electronic Supplementary Material). The number of pollen grains deposited on stigmas from flowers in undisturbed areas was significantly greater than from flowers in disturbed habitats. The greater visitation rate and the greater number of pollen grains deposited on flowers from trees in undisturbed forest resulted in a significantly greater fruit set for trees in these areas. Our study demonstrates the negative effect that habitat disruption has on bat pollinators in tropical dry forest ecosystems and documents the negative consequences for the plants they pollinate.     

Direct evidence for the cycling of fig wasps within one male fig tree

Fig wasps can only survive when flowering fig trees are present all the year around. Ficus trees can only reproduce if they are pollinated by highly specific wasps. In highly seasonal habitats, when only few trees occur at a specific site, gaps in fruiting may lead to the extinction of the local pollinator population. This paper demonstrates that in a dioecious fig tree, Ficus hirta , the fig wasp population can be maintained successfully within an individual plant, through the strong intra-tree asynchrony in flowering. By experimentally bagging trees, we showed that the pollinating wasps ( Blastophaga javana hilli ) could live for two generations, and the non-pollinating wasps ( Sycoscapter sp.) for up to three generations in a closed intra-tree system. However, there was a sharp decline in wasp abundance, deviating sex ratios and decreasing flower occupancy before their ultimate extinction, indicating that the wasp populations were not sustainable. This phenological strategy may enable dioecious figs, which are not constrained by the cost of selfing, to occupy a wider breadth of niches in both tropical and seasonal habitats.     

Reproductive phenology, life-forms, and habitats of the Venezuelan Central Plain

Reproductive phenology of 171 plant species belonging to 57 families of angiosperms was studied according to life-forms in four habitat types in a savanna-forest mosaic on the Venezuelan Central Plain. Flowering, unripe fruit, and mature fruit patterns were affected significantly according to life-forms and habitats respectively. Production of flowers, unripe fruits, and mature fruits showed marked seasonality for all habitats except for the forest. Flowering peaked during the rainy season, and fruiting peaked toward the end of the rainy season. The savanna and the disturbed area had similar proportions of species that flowered over the year. The percentage of species with unripe fruits produced throughout the year was more seasonal for the disturbed area than for the other habitats. Mature fruit patterns showed an increase during the late rainy season for the ecotone and savanna. A large number of herbaceous (annual and perennial) and liana species flowered during the wet season, and a smaller fraction flowered during the dry season; and trees, shrubs, and epiphytes increased flowering activity during the dry season. Unripe fruit patterns were similar to those of flowering for all life-forms, however, tree species were less seasonal. Mature fruit production by shrubs peaked in the period of maximum rainfall, while the peak for perennial herbs was in the late rainy season and the peak for annual herbs was during the transition between the rainy season and the dry season. The largest proportion of tree and liana species with ripe fruits occurred during the dry season. Differences among phenological patterns in habitats were caused mainly by life-forms and promote a wider distribution of reproductive events in habitats and overall community in the Venezuelan Central Plain.     

Fish habitat association in an Ozark stream

Synopsis Associations of fishes in physically distinct habitats (riffles, inlets and pools) of Flint Creek were studied to evaluate critically the habitat-guild concept — the notion that fishes associate with patches of stream habitat in discrete groups. There was little evidence of significant interspecific association at the habitat level. Most fishes were very generalized in their habitat-use patterns. Faunal similarity between habitats was unrelated to physical-habitat similarity. Assemblages from physically distinct habitats were little different from those from physically similar habitats. The structure of the associations (constancy within groups of commonly occurring species) varied seasonally and from site to site. There were constant associations in pools from summer through fall and this coincided with conditions of high fish density and low food availability, suggesting that the pattern resulted from past or present interaction between species. However, the timing also coincided with recruitment of young. Pools were the favored habitats of young-of-year fishes which dominated assemblages in these areas during summer and fall months. This apparently adaptive pattern of habitat association, operating in tandem with local reproductive success could have been responsible for the constancy observed in pools. Most of the species considered here made use of a variety of habitat conditions over the course of their life histories. Individual patches of habitat satisfied the needs of few fish, and thus, seemed too small a scale for the study of community-assembly mechanisms. There was better evidence of interspecies association at the scale of two or more of these habitat areas combined.     

Do baseline glucocorticoids simultaneously represent fitness and environmental quality in a declining aerial insectivore?

Glucocorticoids (GCs) are often interpreted as indicators of disturbance, habitat quality, and fitness in wild populations. However, since most investigations have been unable to examine habitat variability, GC levels, and fitness simultaneously, such interpretations remain largely unvalidated. We combined a quantification of two habitat types, a manipulation of foraging ability (feather‐clipping just prior to nestling rearing), multiple baseline plasma GC measures, and multi‐year reproductive monitoring to experimentally examine the linkages between habitat quality, GCs, and fitness in female tree swallows Tachycineta bicolor. Control females experiencing the higher early‐season food resources of inland–pasture habitat laid larger clutches, but fledged an equal number but lower mass offspring compared to those in riparian–cropland habitat. Despite these differences in reproductive success, females nesting in the two habitat types did not differ in baseline GC levels at the early‐ or late‐breeding stage. Feather‐clipping reduced provisioning rate in both habitat types. However, baseline GC levels were affected in a habitat‐specific way; only individuals in inland–pasture habitats showed an increase in GCs. Despite this difference in GC levels, the manipulation did not influence offspring mass, reproductive output, adult return rate (a proxy for survival) to the following year, or reproductive success in the subsequent year. Nonetheless, regardless of treatment, individuals with higher GC levels during the late breeding stage returned in the following year with higher GC levels at incubation, indicating a long‐term effect on future GC levels. Our results indicate that environmental changes (e.g. foraging conditions) can have consequences for body condition, behaviour, and current and future baseline GC levels without concomitant influences on fitness, and that differences in fitness components between habitats may not be reflected in baseline GC levels. These results illustrate that baseline GCs may not simultaneously reflect environmental quality and fitness, potentially limiting their application in ecological and conservation settings.     

Complementary fruiting phenologies facilitate sharing of one pollinator fig wasp by two fig trees

Aims Most pollinator fig wasps are host plant specific, with each species only breeding in the figs of one fig tree species, but increasing numbers of species are known to be pollinated by more than one fig wasp, and in rare instances host switching can result in Ficus species sharing pollinators. In this study, we examined factors facilitating observed host switching at Xishuangbanna in Southwestern (SW) China, where Ficus squamosa is at the northern edge of its range and lacks the fig wasps that pollinate it elsewhere, and its figs are colonized by a Ceratosolen pollinator that routinely breeds in figs of F. heterostyla .Methods We recorded the habitat preferences of F. squamosa and F. heterostyla at Xishuangbanna, and compared characteristics such as fig size, location and colour at receptive phase. Furthermore, the vegetative and reproductive phenologies in the populations of F. squamosa and F. heterostyla were recorded weekly at Xishuangbanna Tropical Botanical Garden for 1 year.Important findings Ficus squamosa is a shrub found near fast-flowing rivers, F. heterostyla is a small tree of disturbed forest edges. Although preferring different habitats, they can be found growing close together. Both species have figs located at or near ground level, but they differ in size when pollinated. Fig production in F. squamosa was concentrated in the colder months. F. heterostyla produced more figs in summer but had some throughout the year. The absence of its normal pollinators, in combination with similarly located figs and partially complementary fruiting patterns appear to have facilitated colonization of F. squamosa by the routine pollinator of F. heterostyla. The figs probably also share similar attractant volatiles. This host switching suggests one mechanism whereby fig trees can acquire new pollinators and emphasizes the likely significance of edges of ranges in the genesis of novel fig tree–fig wasp relationships.     

陕北沙地小叶杨“小老树”的水力适应性

以黄土高原"小老树"发生面积最大的树种-小叶杨为例,研究了不同水分生境下(水分相对好的沟道和干旱的梁坡片沙地,分别标记为生境A和生境B)小叶杨的生长、光合、水力学特性等,试图探讨小叶杨"小老树"对干旱生境的适应机制。结果表明:生境B小叶杨树高、地径、1 m树高处直径明显小于生境A,同时其主茎顶端枯枝长度大于生境A;生境B小叶杨叶净光合速率和气孔导度明显低于生境A。两种生境下小叶杨黎明前和正午叶水势无显著差异,生境B小叶杨正午时小枝枝干的比导水率明显低于生境A,但两种生境的比叶导水率则无显著差异,生境B小叶杨的Huber值明显大于生境A。生境B小叶杨枝干的P50(导水率损失50%时所对应的木质部水势)比生境A低约0.76 MPa左右,其气孔关闭的水势比生境A晚0.2 MPa左右,生境B小叶杨水分传输安全距离明显大于生境A。表明干旱生境下小叶杨高Huber值和低气孔导度有助于其叶水分关系维持相对稳定,低光合速率和维持大的水分传输安全距离所需的木质部碳投资增加是小叶杨形成"小老树"的重要原因。     

Mycorrhizas in the Kakadu region of tropical Australia

This research represents the first part of a study which aimed to characterize the role of mycorrhizal associations in undisturbed and disturbed habitats in the Alligator Rivers Region of the Northern Territory of Australia. This is a seasonally dry tropical region with a climate consisting of a long dry season and a monsoonal wet season. Intact soil cores were sampled from 22 sites in this region, representing eucalypt savanna woodland, wetland, rocky hill and rainforest habitats. Clover, sorghum and eucalypt seedlings were grown in these cores in bioassays to measure the inoculum potential of vesicular-arbuscular mycorrhizal (VAM) and ectomycorrhizal (ECM) fungi. Propagules of VAM fungi were concentrated in the surface horizon, and were not adversely affected by 6 months dry storage of soil. Bioassays detected VAM fungus propagules at all sites, but these were less numerous in three sites with sparse herbaceous vegetation (a shrub-dominated woodland site, a sandstone area and a disturbed gravel pit without topsoil), than in other woodland sites. Propagules of VAM fungi were particularly numerous in soil from a rainforest habitat, which had much denser plant cover than any of the savanna sites. Propagules of ECM fungi colonized eucalypt seedling roots in some cores from all sites, except two wetland areas and a disturbed area without eucalypt trees. Physical and chemical properties of soils varied between sites and some properties (texture, organic carbon, etc.) were correlated with the inoculum potential of VAM fungi.     

Seasonal changes in subarctic sea urchin populations from different habitats

This paper documents seasonal variation in certain sea urchin (Strongylocentrotus polyacanthus) characteristics in habitats of varying environmental conditions. At Shemya Island, Alaska, three habitat types [dense kelp beds, intermediate kelp beds, and algal barrens (low to no foliose algal cover)] were monitored seasonally from September 1995 to August 1996, for live and drift foliose algae. In general, drift algal abundance was greater in areas with more attached kelp, but this varied with season. Along with drift algae, sea urchin density, test size diameter, gonad and nutrition indices, and mobility were seasonally sampled within each habitat. Densities were highest in the algal barrens and lowest in the kelp beds. Seasonally, densities varied between summer/fall, and winter/spring, with lower numbers in the winter/spring. Test size was largest in the kelp habitats when compared to the intermediate or barren sites. Test size was seasonally consistent in the kelp habitats but not in the intermediate or barren sites. Here, test size did vary depending on season (larger urchins were found in winter). The gonad index showed much seasonal variation at the kelp and intermediate kelp sites, but was relatively more stable over time in the barren habitats. Between habitats, gonad and nutrition indices were larger in areas with kelp. Urchin movement varied seasonally between habitats, with more overall movement and variation in barren habitats. These results illustrate the importance of small-scale temporal and spatial variation. Monitoring for 1 year demonstrated that certain parameters varied more in areas of higher foliose algal cover (gonad indices), while other parameters varied more in low kelp areas (test size and movement). These results suggest that studies involving urchins should consider both time of year and overall algal community composition when conducting any type of experimental or monitoring work.     

Theoretical habitat templets, species traits, and species richness: 548 plant and animal species in the Upper Rhône River and its floodplain

• 1 For practical reasons, conceptual developments in community ecology are usually based on studies of a restricted systematic group. The cooperation of thirty or so specialists in the synthesis of long-term ecological research on the Upper Rhône River, France, provided a unique occasion to investigate relationships among species traits, the habitat utilization by species, the relationship between species traits and habitat utilization, and trends of species traits and species richness in the framework of spatial-temporal habitat variability for 548 species of plants (Hyphomycetes, aquatic macrophytes, floodplain vegetation) and animals (Tricladida, Oligochaeta, several groups of Crustacea, Insecta and Vertebrata).
• 2 Using correspondence analysis, 100 modalities of eighteen species traits were examined; the resulting typology demonstrates that systematic groups are the most important elements for separating species traits such as size, fecundity of individuals, parental care, mobility, body form, and food type. Small species have an intermediate number of descendants per reproductive cycle and few reproductive cycles both per year and per individual; in contrast, large species have a high number of descendants per reproductive cycle and few reproductive cycles per year but many potential reproductive cycles per individual.
• 3 The analysis of habitat utilization in the Upper Rhône River and its floodplain by the 548 species demonstrated a vertical gradient separating interstitial from superficial habitats; a transverse gradient for superficial habitats from the main channel towards more terrestrial ones is also evident.
• 4 Because of a significant (P < 0.01) relationship between species traits and habitat utilization, traits such as size, fecundity of individuals, parental care, tolerance to variation in humidity, and respiration are arranged along the vertical and transverse habitat gradient. Size, the number of reproductive cycles per individual, and the tolerance to variation of humidity increases from permanent waters to temporary waters, aggrading habitats, and terrestrial habitats.
• 5 Species traits showed significant (P < 0.01) trends in the framework of spatial-temporal habitat variability and were compared with predictions based on the river habitat templet. Although each habitat showed a mixture of species traits at low temporal and spatial variability, and at high variability sites, trends corresponded to predictions for three traits (number of descendants per reproductive cycle, number of reproductive cycles per individual, attachment to soil or substrate) along a gradient of increasing temporal habitat variability.
• 6 The species richness of each habitat within the Upper Rhône River and its floodplain significantly (P = 0.03) increased as the spatial variability of habitats increased but there is no statistical correlation between spedes richness and temporal variability. An altemative hypothesis predicting that fewer spedes per resource occur in temporally stable habitats is also not supported.

     

Environmental effects on variation and covariation in reproductive traits of Western Bluebirds

Summary Environmental conditions can influence the expression and correlations of phenotypic traits. I studied phenotypic plasticity in reproductive traits of Western Bluebirds breeding in northern Arizona. Data collected over 4 years on two contrasting habitats identified significant spatial and temporal variation in bluebird reproduction. Clutch size was similar over different environmental conditions whereas timing of clutch initiation, percent fledging success, and frequency of second nest attempts were flexible. Correlations between traits varied widely—often changing sign—among samples from different years or habitats. Correlations of traits with reproductive success were also dependent on environmental conditions. Variation in traits reflected behavioral responses by nesting adults to differences in time for breeding and feeding conditions. Density of trees differed between habitats and had opposing effects on these environmental variables; breeding seasons were generally longer, but feeding rates to nestlings were lower on the more open habitat. Late Spring snows delayed reproduction and increased the importance of limited time for breeding; feeding conditions were more influential following a dry Spring. This and other studies illustrate that data on phenotypic plasticity are important when evaluating the ecological and evolutionary forces underlying life histories.     

Microdistribution and habitat selection in Drosophila subobscura Collin

Microdistribution and habitat selection were investigated in a population of Drosophila subobscura near Leeds, Yorkshire. Microdistribution was examined along a transect running through a deciduous woodland. Two main types of habitat were recognized, those with dry soil and a closed canopy of mature trees (dry and dark) and those with wet soil and an open canopy of mature trees (wet and light). Flies were much more frequent, judged by their attendance at baited traps, in the dry/dark habitat. Flies taken from both habitat types, marked with different coloured fluorescent dust and released at a point mid-way between the original habitats, tended to return to their area of initial capture.     

Distinct Leaf‐trait Syndromes of Evergreen and Deciduous Trees in a Seasonally Dry Tropical Forest

In seasonally dry tropical forests, tree species can be deciduous, remaining without leaves throughout the dry season, or evergreen, retaining their leaves throughout the dry season. Deciduous and evergreen trees specialize in habitats that differ in water availability (hillside and riparian forest, respectively) and in their exposure to herbivore attack (seasonal and continuous, respectively). We asked whether syndromes of leaf traits in deciduous and evergreen trees were consistent with hypothesized abiotic and biotic selective pressures in their respective habitat. We measured seven leaf traits in 19 deciduous and 11 evergreen tree species in a dry tropical forest in Western Mexico, and measured rates of herbivory on 23 of these species. We investigated the covariance of leaf traits in syndromes related to phenology and associated physiology, and to anti‐herbivory defense. We found evidence for syndromes that separated phenological strategies among four traits: toughness, water content, specific leaf area, and carbon:nitrogen (C:N) ratios. We found a trade‐off between two other traits: trichomes and latex. Overall, evergreen species exhibited lower rates of herbivory than deciduous species. Lower rates of herbivory were explained by a syndrome of higher toughness, lower water content, and higher C:N ratios, which are traits representative of evergreen trees. Phenology and trait syndromes did not exhibit significant phylogenetic signal, consistent with the hypothesis of evolutionary convergence among phenologies and associated leaf‐trait syndromes. Our results suggest that deciduous and evergreen trees could respond to differential water availability and herbivory in their respective habitats by converging on distinct leaf‐trait syndromes. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Diversity of dry forest epiphytes along a gradient of human disturbance in the tropical Andes

Question: Disturbance effects on dry forest epiphytes are poorly known. How are epiphytic assemblages affected by different degrees of human disturbance, and what are the driving forces? Location: An inter‐Andean dry forest landscape at 2300 m elevation in northern Ecuador. Methods: We sampled epiphytic bryophytes and vascular plants on 100 trees of Acacia macracantha in five habitats: closed‐canopy mixed and pure acacia forest (old secondary), forest edge, young semi‐closed secondary woodland, and isolated trees in grassland. Results: Total species richness in forest edge habitats and on isolated trees was significantly lower than in closed forest types. Species density of vascular epiphytes (species per tree) did not differ significantly between habitat types. Species density of bryophytes, in contrast, was significantly lower in edge habitat and on isolated trees than in closed forest. Forest edge showed greater impoverishment than semi‐closed woodland and similar floristic affinity to isolated trees and to closed forest types. Assemblages were significantly nested; habitat types with major disturbance held only subsets of the closed forest assemblages, indicating a gradual reduction in niche availability. Distance to forest had no effect on species density of epiphytes on isolated trees, but species density was closely correlated with crown closure, a measure of canopy integrity. Main conclusions: Microclimatic changes but not dispersal constraints were key determinants of epiphyte assemblages following disturbance. Epiphytic cryptogams are sensitive indicators of microclimate and human disturbance in montane dry forests. The substantial impoverishment of edge habitat underlines the need for fragmentation studies on epiphytes elsewhere in the Tropics.     

Temporal plasticity in thermal‐habitat selection of burbot Lota lota a diel‐migrating winter‐specialist

In this study, animal‐borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter‐specialist diel‐migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12–14° C) optimal for hunting and feeding during non‐reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non‐reproductive periods, respectively, active selection was limited to selection for 4–6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night‐time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal‐habitat selection was a good predictor of night‐time habitat occupancy in a diel‐migrating species. Together, these results show that thermal‐habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.     

The role of dispersal ability, climate and spatial separation in shaping biogeographical patterns of phylogenetically distant plant groups in seasonally dry Andean forests of Bolivia

Aim To assess biogeographical patterns of Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta in Bolivian Andean seasonally dry forest islands and to explain current floristic differences between these islands by means of extrinsic (precipitation, elevation) and intrinsic (dispersal ability) factors. Location Ten isolated and disjunct seasonally dry forest areas in the Bolivian Andes and the adjacent seasonal forest areas of the Chiquitanía and Chaco regions. Methods We collated species data from recently updated and revised taxonomic treatments and herbarium collections for Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta, constructed floristic distance matrices to estimate beta diversity at the study sites and subjected them to Mantel correlation analyses. Multiple regressions on distance matrices allowed us to test the influence of geographical distance and environmental (elevation and precipitation) differences on floristic differentiation. Results Acanthaceae and Bromeliaceae, and to a lesser extent Cactaceae, showed coincident biogeographical patterns and suggested the presence of two seasonally dry forest groups in Andean Bolivia: one including all small isolated northern dry valleys and another including all southern valleys with connections to the lowland seasonal forests of the Chiquitanía and the Chaco. Most of the variation in the floristic distance matrices in these plant groups, with seed dispersal typically restricted to short distances, was explained by spatial separation between habitat islands. In contrast, pteridophytes showed a different biogeographical pattern. Their floristic differences between sites were determined by the environmental variables. The anemochorous and spore‐based dispersal system of this plant group seems to be a highly effective mechanism allowing pteridophytes to easily reach even the isolated dry valleys in inter‐Andean Bolivia. Main conclusions Current biogeographical patterns in dry Andean habitat islands can provide insights into the factors that control the processes of community assembly. We show that differences in community composition of phylogenetically distant plant groups in the understorey of seasonally dry forest islands can be explained by a combination of the habitat characteristics where the group is present (either precipitation, elevation or both) and, more interestingly, by group specific dispersal limitation (as inferred by geographical distance between island habitats).     

Phenology of Ficus variegata in a seasonal wet tropical forest at Cape Tribulation, Australia

Abstract. We studied the phenology of 198 mature trees of the dioecious fig Ficus variegata Blume (Moraceae) in a seasonally wet tropical rain forest at Cape Tribulation, Australia, from March 1988 to February 1993. Leaf production was highly seasonal and correlated with rainfall. Trees were annually deciduous, with a pronounced leaf drop and a pulse of new growth during the August-September drought. At the population level, figs were produced continually throughout the study but there were pronounced annual cycles in fig abundance. Figs were least abundant during the early dry period (June-September) and most abundant from the late dry season (October-November) through the wet season (December-April). The annual peak in reproduction actually reflected two staggered peaks arising from gender differences in fig phenology. In this dioecious species, female and male trees initiated their maximal fig crops at different times and flowering was to some extent synchronized within sexes. Fig production in the female (seed-producing) trees was typically confined to the wet season. Male (wasp-producing) trees were less synchronized than female trees but reached a peak level of fig production in the months prior to the onset of female fig production. Male trees were also more likely to produce figs continually. Asynchrony among male fig crops during the dry season could maintain the pollinator population under adverse conditions through within- and among-tree wasp transfers.     

Spatial and Temporal Distribution of Northern Waterthrushes Among Nonbreeding Habitats in Southwestern Puerto Rico1

We surveyed nonbreeding Northern Waterthrushes (Seiurus noveboracensis) in several coastal habitats in southwestern Puerto Rico, West Indies. Waterthrush abundance was highest (mean = 2.2/point) in well‐developed mangrove habitats characterized by large trees and standing water, and lowest (mean = 0.1/point) in dry coastal scrub and savannah. Within the latter habitats, waterthrushes were more common in moist microhabitats such as temporary ponds and dry washes. Abundance in most habitats declined between October and January, probably a result of the presence of transients during the October surveys, Between January and March, abundance in mature red mangrove (Rhizophora mangle) forests increased dramatically, suggesting that this habitat provides a refuge for birds at the end of the dry season and prior to northward migration. In conjunction with other data demonstrating the use of coastal red mangroves as nocturnal roosting sites, these results suggest that mangroves are the most important nonbreeding habitat for this species. Conservation of this globally threatened habitat may thus be important for the long‐term stability of waterthrush populations.