Spatial structure and genetic diversity of three tropical tree species with different habitat preferences within a natural forest

Analyses of the spatial distribution pattern, spatial genetic structure and genetic diversity were carried out using a 33-ha plot in a hill dipterocarp forest for three dipterocarps with different habitat preferences, i.e. Shorea curtisii on the ridges, Shorea leprosula in the valleys and Shorea macroptera both on the ridges and in the valleys. The significant spatial aggregation in small-diameter trees of all the three species was explained by limited seed dispersal. At the large-diameter trees, only S. macroptera showed random distribution and this might further prove that S. macroptera is habitat generalist, whilst S. curtisii and S. leprosula are habitat specific. The levels of genetic diversity estimated based on five microsatellite loci were high and comparable in all the three studied species. As the three studied species reproduced mainly through outcrossing, the observed high levels of genetic diversity might support the fact that the plant mating system can be used as guideline to infer the levels of genetic diversity, regardless of whether the species is habitat specific or habitat generalist. The lack of spatial genetic structure but significant aggregation in the small-diameter trees of all the three species might indicate limited seed dispersal but extensive pollen flow. Hence, if seed dispersal is restricted but pollen flow is extensive, significant spatial aggregation but no spatial genetic structure will be observed at the small-diameter trees, regardless of whether the species is habitat specific or habitat generalist. The inferred extensive pollen flow might indicate that energetic pollinators are involved in the pollination of Shorea species in the hill dipterocarp forests.     

Changes in tree reproductive traits reduce functional diversity in a fragmented Atlantic forest landscape

Functional diversity has been postulated to be critical for the maintenance of ecosystem functioning, but the way it can be disrupted by human-related disturbances remains poorly investigated. Here we test the hypothesis that habitat fragmentation changes the relative contribution of tree species within categories of reproductive traits (frequency of traits) and reduces the functional diversity of tree assemblages. The study was carried out in an old and severely fragmented landscape of the Brazilian Atlantic forest. We used published information and field observations to obtain the frequency of tree species and individuals within 50 categories of reproductive traits (distributed in four major classes: pollination systems, floral biology, sexual systems, and reproductive systems) in 10 fragments and 10 tracts of forest interior (control plots). As hypothesized, populations in fragments and control plots differed substantially in the representation of the four major classes of reproductive traits (more than 50% of the categories investigated). The most conspicuous differences were the lack of three pollination systems in fragments--pollination by birds, flies and non-flying mammals--and that fragments had a higher frequency of both species and individuals pollinated by generalist vectors. Hermaphroditic species predominate in both habitats, although their relative abundances were higher in fragments. On the contrary, self-incompatible species were underrepresented in fragments. Moreover, fragments showed lower functional diversity (H' scores) for pollination systems (-30.3%), floral types (-23.6%), and floral sizes (-20.8%) in comparison to control plots. In contrast to the overwhelming effect of fragmentation, patch and landscape metrics such as patch size and forest cover played a minor role on the frequency of traits. Our results suggest that habitat fragmentation promotes a marked shift in the relative abundance of tree reproductive traits and greatly reduces the functional diversity of tree assemblages in fragmented landscapes.     

High genetic diversity and contrasting fine-scale spatial genetic structure in four seasonally dry tropical forest tree species

In this study we compared population structure, genetic diversity and fine-scale spatial genetic structure (SGS) in four Bignoniaceae tree species, Handroanthus chrysotrichus, H. impetiginosus, Tabebuia roseoalba and H. serratifolius in a remnant of seasonally dry tropical forest in Central-West Brazil, based on polymorphisms at six microsatellite loci. All species, except T. roseoalba, presented the inverted ‘J’ population structure indicating recruitment of juveniles. Juveniles presented a clumped distribution suggesting limitation in dispersal or patchy distribution of suitable microhabitat for recruitment. All species showed high levels of polymorphism and genetic diversity but without a clear pattern of distribution among life stages. The SGS was significant for all species, except T. roseoalba, but the pattern and strength of the spatial genetic structure differed among species. Handroanthus serratifolius had stronger SGS with significant kinship until 77 m. For H. impetiginosus and H. chrysotrichus, kinship was significant just until 23 and 6 m, respectively. Despite the high genetic diversity, all species showed low number of adults and high fixation indices suggesting that habitat fragmentation and disturbance have been affecting these populations in Central-West Brazil.     

Clonal structure and genetic diversity of three desert phreatophytes

The objective of this paper was to assess clone sizes of three perennial desert plant species with AFLP markers and to relate them to clonal and genetic diversity and to hydroecology. The study was carried out at the southern rim of the Taklamakan Desert, where sexual regeneration is only possible shortly after rare flooding events, resulting in rarely established cohorts with subsequent extensive vertical growth and horizontal clonal spread. In this environment, repeated seedling establishment is excluded. We expected decreasing clonal and genetic diversity with increasing clone size and increasing distance to the groundwater table and a common response pattern among all study species. Maximum sizes of Populus euphratica and Alhagi sparsifolia clones were 121 ha and 6.1 ha, respectively, while Tamarix ramosissima clones reached a maximum size of only 38 m(2). In P. euphratica and A. sparsifolia, clonal diversity declined with increasing clone size and increasing distance to the groundwater table, while genetic diversity remained unaffected. Tamarix ramosissima differed from the other species because of a much smaller clonality. Clone size and clonal diversity were found to be good proxy variables for clone age. Despite the considerable age of the clones, genetic diversity is maintained in the populations.     

Linking traits to species diversity and community structure in phytoplankton

In addition to answering Hutchinson’s question “Why are there so many species?”, we need to understand why certain species are found only under certain environmental conditions and not others. Trait-based approaches are being increasingly used in ecology to do just that: explain and predict species distributions along environmental gradients. These approaches can be successful in understanding the diversity and community structure of phytoplankton. Among major traits shaping phytoplankton distributions are resource utilization traits, morphological traits (with size being probably the most influential), grazer resistance traits, and temperature responses. We review these trait-based approaches and give examples of how trait data can explain species distributions in both freshwater and marine systems. We also outline new directions in trait-based approaches applied to phytoplankton such as looking simultaneously at trait and phylogenetic structure of phytoplankton communities and using adaptive dynamics models to predict trait evolution.     

Leaf habit does not predict leaf functional traits in cerrado woody species

Plant species with a high leaf life span (LLS) commonly have a low specific leaf area (SLA), leaf nitrogen per unit mass (N), and phosphorous concentration (P), whereas species with low LLS have a high SLA, N and P. However, LLS tends to be longer in species growing in low-nutrient soils and, therefore, differences in LLS and other leaf traits may not be consistent with a plant classification according to leaf habit. Here we investigated whether leaf habit is consistent with leaf economic spectrum trade-offs in cerrado (a Neotropical savanna) woody species. We analyzed the SLA, N and P of 125 woody species with a distinct leaf habit (deciduous, semideciduous, brevideciduous or evergreen). We also gathered data on the LLS (33 species), maximum net photosynthesis per leaf area (A_area, 56 species) and per leaf mass (A_mass, 31 species), comprising the most extensive database analyzed so far for the cerrado. Differences among leaf habit groups were tested using generalized linear mixed models and ANOVA. We did not find differences in SLA and N among species with a distinct leaf habit, but deciduous species had a higher leaf P concentration than evergreens. Species did not differ in LLS and A_mass, but A_area varied among groups. Semideciduous species had higher A_area values than deciduous and brevideciduous species, but all other groups had similar A_area values. Because of the small difference in the LLS, SLA, leaf N, leaf P and maximum net photosynthesis, we argue that deciduous, brevideciduous, semideciduous and evergreen species may not constitute different functional groups in cerrado woody species.     

Impacts of forest gaps on butterfly diversity in a Bornean peat-swamp forest

Forest degradation is leading to widespread negative impacts on biodiversity in South-east Asia. Tropical peat-swamp forests are one South-east Asian habitat in which insect communities, and the impacts of forest degradation on them, are poorly understood. To address this information deficit, we investigated the impacts of forest gaps on fruit-feeding butterflies in the Sabangau peat-swamp forest, Central Kalimantan, Indonesia. Fruit-baited traps were used to monitor butterflies for 3 months during the 2009 dry season. A network of 34 traps (n_gap = 17, n_shade = 17) was assembled in a grid covering a 35 ha area. A total of 445 capture events were recorded, comprising 384 individuals from 8 species and 2 additional species complexes classified to genera. On an inter-site scale, canopy traps captured higher species richness than understory traps; however, understory traps captured higher diversity within each site. Species richness was positively correlated with percent canopy cover and comparisons of diversity indices support these findings. Coupled with results demonstrating morphological differences in thorax volume and forewing length between species caught in closed-canopy traps vs. those in gaps, this indicates that forest degradation has a profound effect on butterfly communities in this habitat, with more generalist species being favored in disturbed conditions. Further studies are necessary to better understand the influences of macro-habitat quality and seasonal variations on butterfly diversity and community composition in South-east Asian peat-swamp forests.     

幕阜山森林群落结构与物种多样性研究

幕阜山地处中亚热带-北亚热带过渡地带,物种资源丰富.通过对其典型样地的调查,分别采用Shannon-Wiener指数、Simpson指数和Pielou均匀度指数作为测度指标,研究了幕阜山地区森林群落结构及其物种多样性特征.结果表明,该地区主要有21个森林群落类型.其中常绿阔叶林中,物种丰富度指数与多样性指数在群落梯度上的总体趋势均为灌木层相对高于乔木层,乔木层相对高于草本层;在落叶阔叶林中,其丰富度指数的趋势为灌木层＞草本层和乔木层,而在草本层与乔木层间是波动的,多样性指数的趋势为灌木层＞草本层＞乔木层;在针叶林中,物种丰富度、多样性指数表现的总趋势基本一致,即灌木层的丰富度相对较高,其次为草本层,乔木层的相对较小.在其他群落类型中,多样性指数、均匀度指数在乔木层、灌木层和草本层则表现出多样化的趋势;另外,从总体上看,各种指数在海拔梯度上并未表现出明显的规律性.     

Contrasting relationships between species diversity and genetic diversity in natural and disturbed forest tree communities

? This study aimed to reveal species-genetic diversity correlations (SGDCs) and their underlying mechanisms in natural and disturbed forests. ? A community survey and molecular analyses were carried out to compare species diversity (SD), the genetic diversity of the dominant tree species Euptelea pleiospermum (GD), the altitudinal patterns of SD and GD, SGDC, genetic differentiation (F(ST) ), community divergence (F(ST) -C), effective population size (N(e) ), and recent migration rate between mountain riparian forests along the Yandu (natural) and Nan (disturbed) rivers. ? In natural forests, both SD and GD showed a unimodal altitudinal pattern and GD was positively correlated with SD, whereas a unimodal pattern and positive SGDC were not found in the disturbed forests. SD and F(ST) at the natural sites were higher than those at the disturbed sites. However, there were no significant differences in GD, F(ST) -C, N(e) or recent migration rate between the natural and disturbed sites. ? A correlation between the patterns of SD and GD along a geographical gradient (e.g. altitude) is an important driver of positive SGDC. The absence of positive SGDC in the disturbed forests may result from reduced SD but unaffected GD, indicating nonparallel changes in SD and GD. This study furthermore cautions against generalizations about changes in SD and GD following disturbance.     

Horizontal, but not vertical canopy structure is related to stand functional diversity in a subtropical slope forest

The aim of this study was to analyse the relation of horizontal and vertical canopy structure to tree functional diversity of a highly diverse subtropical broad-leaved slope forest, stratified for different successional stages. This is of particular interest because many key ecosystem processes and functions are related to the arrangement of forest canopies. We assessed the effect of stand-related functional diversity (FD_Q, measured as Rao’s quadratic entropy of leaf traits), together with other environmental variables on horizontal [measured as relative crown projection areas (CPA_r)] and vertical [relative crown overlap, coefficients of variation (CV) of crown positioning variables] structure of the upper canopy at the local neighbourhood level. The analyses with mixed effects models revealed a negative relation (p = 0.025; estimate −0.07) between FD_Q and CPA_r. No significant effect of FD_Q on vertical canopy structure has been found (p > 0.05). The findings are discussed with regard to resource partitioning and niche differentiation of canopy and sub-canopy species. Successional stage positively impacted the CV of crown length (p = 0.019; estimate 0.03) but did not affect other response variables. The sloping terrain strongly influenced vertical canopy structure as revealed by the significant effect of slope inclination on CV of crown length (p = 0.004; estimate −0.05) and of slope aspect on CV of mean crown height (p = 0.036; estimate −0.03). The high complexity of vertical crown positioning depending on the heterogeneous sloping terrain of the study area may have obscured relations of FD_Q to vertical canopy structure.     

Impacts of silviculture on genetic diversity in the native forest species Eucalyptus sieberi

Potential impacts of regeneration practices ongenetic diversity in the Australian nativeforest species Eucalyptus sieberi L.A.S.Johnson. (silvertop ash) were assessed usingDNA markers. Three different silviculturaltreatments were examined: clear-felling withaerial re-sowing, and the seed tree system withsite preparation by either burning ormechanical disturbance. In addition, twounharvested stands were chosen as controls. Atotal sample of 825 trees were genotyped at 35Mendelian markers: 26 single-copy nuclear RFLPsand 9 microsatellites. No significantdifferences were found among the treatments inany of four population genetic statistics:allelic richness, effective number of alleles,expected heterozygosity and the panmictic index(f). Rare alleles were prevalent, and a MonteCarlo simulation showed that the apparent lossof four rare alleles from the saplingregenerants was highly statisticallysignificant. There was no evidence for recentbottlenecks from analyses of either the levelsof expected heterozygosity relative to thatexpected under mutation drift equilibrium, orthe allele frequency profiles. A dendrogram ofthe relationships between the sampledpopulations suggested that the seed tree systemmay result in the promotion of genetic drift(slight expansion of the dendrogram) whileaerial re-sowing of clear falls with the sameseedlot will lead to genetic homogenisation(contraction of the dendrogram). The apparentgenetic robustness of E. sieberi tonative forest regeneration practices isattributed to its local abundance combined withthe favourable properties of its reproductivebiology, as well as to the limitation that onlya single rotation was examined.     

Comparison of the fine-scale genetic structure of three dipterocarp species

We investigated the fine-scale genetic structure of three tropical-rainforest trees, Hopea dryobalanoides, Shorea parvifolia and S. acuminata (Dipterocarpaceae), in Peninsular Malaysia, all of which cooccurred within a 6-ha plot in Pasoh Forest Reserve. A significant genetic structure was found in H. dryobalanoides, weaker (but still significant) genetic structure in S. parvifolia and nonsignificant structure in S. acuminata. Seeds of all three species are wind dispersed, and their flowers are thought to be insect pollinated. The most obvious difference among these species is their height: S. parvifolia and S. acuminata are canopy species, whereas H. dryobalanoides is a subcanopy species. Clear differences were also found among these species in their range of seed dispersal, which depends on the height of the release point; so taller trees disperse their seed more extensively. The estimates of seed dispersal area were consistent with the degree of genetic structure found in the three species. Therefore, tree height probably had a strong influence on the fine-scale genetic structure of the three species.     

Effects of site and fruit size on the composition of avian frugivore assemblages in a fragmented Afrotropical forest

Factors influencing the interaction between fruiting trees and their frugivorous seed dispersers in fragmented Afrotropical landscapes are poorly known. With the use of Mantel statistics we analysed assemblages of frugivorous birds on 58 individual trees belonging to 11 species growing in seven Kenyan cloud forest fragments. Overall, frugivores showed little specialization on particular trees. Fruit size explained a substantial amount of the variation in frugivore assemblages among different tree species at the same site. In addition, frugivore assemblages on conspecific trees were significantly more similar when the trees occurred at the same site. This location effect was attributable to the different sites and forest fragments (of different sizes and disturbance levels) varying in the densities and composition of their avian frugivores, vegetation composition and tree fruiting phenologies. It was consolidated further by the low mobility of most of these avian frugivores, particularly their reluctance to cross between forest fragments. Habitat disturbance and fragmentation may therefore have affected fruit selection, with implications for both seed dispersal and regeneration.     

Microsatellite analysis reveals the resilience of genetic diversity within extant populations of three Akebia species to chronic forest fragmentation in China

Plant Ecology - The species of Akebia Decne are well-known medicinal plants and have been used in Chinese herbalism for at least 2000 years. The Akebia fruits have a delicious flavor and...     

Competition and species diversity: removal of dominant species increases diversity in Costa Rican butterfly communities

Biological communities are usually dominated by a few species and show characteristically skewed species abundance distributions. Although niche apportionment and resource competition are sometimes implicated in such patterns, few experimental studies have shown direct links between resource limitation, competition with dominant species and their impacts on the overall diversity and composition of large natural communities. Here I report the results of an experiment in which I first studied species diversity and composition in two Costa Rican nectar-feeding butterfly communities numerically dominated by two species of Anartia butterflies. Then I removed Anartia from these communities to study changes in resource availability, species abundance relationships, community diversity and composition as an outcome of the removal of the dominant competitors. In the face of competition with Anartia , nectar was scarce, species abundance distributions were highly skewed, and species diversity was low in both communities. Within two weeks after the removal of Anartia , there were parallel changes in both communities: competition for nectar reduced and the nectar quantity increased substantially, which facilitated increase in community diversity and resulted in significantly less skewed species abundance distributions. Higher nectar quantity also enabled the distribution of body size and proboscis length of constituent species in the communities to expand at both ends. This study thus experimentally showed that resource competition with the dominant species was excluding many species from the communities, lowering their diversity and skewing relative species abundance relationships. These findings are of fundamental importance for competition theory and community ecology because they indicate ways in which diverse communities may be affected by and recover from competition with dominant species.     

Comparative genetic structure reflects underlying life histories of three sympatric small mammal species in continuous forest of south-eastern Australia

There are strong links between habitat fragmentation, population size and genetic structure. However, to fully understand the long‐term effects of fragmentation on population viability, it is necessary to first understand the relationship between life history traits and genetic characteristics in un‐fragmented habitats. This is best done through comparing patterns of genetic diversity in sympatric species, since relative data may be maximally informative. We compared genetic structure and diversity among three sympatric small mammals – of which two were marsupial species – over a small spatial scale (<4 km) using microsatellite genotypic data from individuals sampled from four grids spaced in a linear fashion. Expected heterozygosity was high for all three species (average H_e range: 0.781–0.886), but the smallest species had significantly higher genetic diversity (both heterozygosity and allelic diversity) than the two larger species, possibly due to it having; 1) large effective population size and little overlap in generations, and/or 2) high mutation rates in large alleles. Genotypic isolation by distance (measured as relatedness) was detected only at the smallest distance of 750 m, for any species. In the two marsupial species F_st, relatedness and percentage of individuals assigned to site of capture were significantly lower in males than in females, corroborating previous reports of male‐biased dispersal. However, sex‐biased dispersal was not detected for the third species (the native bush rat Rattus fuscipes), and presence of significant heterozygous deficits suggested this resulted in inbreeding within kin‐structured demes. We speculate that habitat fragmentation will have differing effects on population dynamics, social organisation and mating systems for the two marsupial species compared to the native murid rodent, due to their differing population structure and divergent inbreeding avoidance mechanisms.     

天祝夏玛林区蝶类区系研究

2008-2010年每年7-9月,在天祝夏玛林区按照不同海拔高度及不同植被类型的自然环境,对蝶类进行了系统的采集,共获得蝶类标本2000号,经整理、鉴定出71种蝶类,隶属于8科50属。其中粉蝶科9属20种,占总种数的28.2%,为优势类群;蛱蝶科15属15种,眼蝶科13属14种,分别占总种数的21.1%和19.7%,为次优势类群;绢蝶科(1属9种)和灰蝶科(8属8种)为常见类群;弄蝶科(2属2种)、凤蝶科(1属2种)和蚬蝶科(1属1种)为罕见类群。区系成分分析结果是,属于古北界的种类有51种,占总种数的71.8%;属于东洋界与古北界兼有种类有14种,占总种数的19.7%;广布种6种,占总种数的8.5%;完全属于东洋界的种类无分布。结果表明,该地区分布的蝶类区系成分以古北界的种类为主。