Landscape genetics of a tropical rescue pollinator

Pollination services are increasingly threatened by the loss and modification of natural habitats, posing a risk to the maintenance of both native plant biodiversity and agricultural production. In order to safeguard pollination services, it is essential to examine the impacts of habitat degradation on the population dynamics of key pollinators and identify potential “rescue pollinators” capable of persisting in these human-altered landscapes. Using a landscape genetic approach, we assessed the impact of landscape structure on genetic differentiation in the widely-distributed tropical stingless bee Trigona spinipes (Apidae: Meliponini) across agricultural landscape mosaics composed of coffee plantations and Atlantic forest fragments in southeastern Brazil. We genotyped 115 bees at 16 specific and highly polymorphic microsatellite loci, developed using next-generation sequencing. Our results reveal that T. spinipes is capable of dispersing across remarkably long distances, as we did not find genetic differentiation across a 200 km range, nor fine-scale spatial genetic structure. Furthermore, gene flow was not affected by forest cover, land cover, or elevation, indicating that reproductive individuals are able to disperse well through agricultural landscapes and across altitudinal gradients. We also found evidence of a recent population expansion, suggesting that this opportunistic stingless bee is capable of colonizing degraded habitats. Our results thus suggest that T. spinipes can persist in heavily-altered landscapes and can be regarded as a rescue pollinator, potentially compensating for the decline of other native pollinators in degraded tropical landscapes.     

The role of remnant forest trees in tropical secondary succession

This paper emphasizes the contribution of remnant trees to the establishment of woody species during succession on abandoned fields and pastures in the Mexican rain forest area, Los Tuxtlas, Veracruz. Remnant trees, original large forest trees left in the clearings by traditional farmers will become natural perching sites for both passing and resident birds. Frugivorous birds drop or regurgitate seeds and fruits which fall under the canopies of remnant trees during their stay, thus contributing to an accumulation of species, which make these remnant trees into ‘regeneration nuclei’. The species transported into these sites belong chiefly to older stages of successional development and reach these otherwise isolated areas, counteracting the depauperization of tropical land, brought about by both intensive and extensive clearing. In a study of seven remnant trees, 29 woody species and two climbers were found, 86% of which are bird dispersed. The total number of species per tree varied from 6 to 15 and was higher under remnant trees with fruits attractive to birds. Floristic variations of the understorey as detected by detrended correspondence analysis was correlated with the relative amount of shade-tolerant primary and late secondary trees versus light dependent pioneers and early successional trees.     

Little evidence for negative effects of an invasive alien plant on pollinator services

Many invasive alien plants occur in large populations with abundant flowers which are highly attractive to pollinators, and thus might affect pollination of co-occurring native species. This study focuses on the invasive Heracleum mantegazzianum and distance-dependent effects on pollination of Mimulus guttatus in abandoned grassland over 2 years. First, we examined pollinator abundance in yellow traps at 0, 10, 30 and 60–200 m from H. mantegazzianum. We then placed M. guttatus plants at the same distances to monitor effects of the invasive species on pollinator visitation and seed set of neighbouring plants. Finally, we conducted a garden experiment to test if deposition of H. mantegazzianum pollen reduces seed set in M. guttatus. No distance effect was found for the number of bumblebees in traps, although the invasive species attracted a diverse assemblage of insects, and visitation of M. guttatus was enhanced close to H. mantegazzianum. This positive effect was not reflected by seed set of M. guttatus, and heterospecific pollen decreased seed set in these plants. Overall there is little evidence for negative effects of the invasive species on pollination of neighbouring plants, and flower visitation even increases close to the invaded patches. The functional role of the invader and suitable control strategies need further clarification, since removal of H. mantegazzianum may actually damage local pollinator populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Oeceoclades maculata, an alien tropical orchid in a Caribbean rainforest

Background and Aims

Undisturbed forest habitat can be relatively impenetrable to invasive, non-native species. Orchids are not commonly regarded as invasive, but some species have become invasive and these generally depend on habitat disturbance. One of the most aggressive orchids is Oeceoclades maculata, a terrestrial species with remarkable ecological amplitude. Originally from tropical Africa, it is now widespread in the neotropics. By associating its local distribution with land-use history and habitat characteristics, it was determined whether O. maculata is dependent on habitat disturbance. It was also investigated whether this exotic orchid occupies the same habitat space as two sympatric native species.

Methods

Six 10 m × 500 m transects were censused in June 2007 on the 16-ha Luquillo Forest Dynamics Plot, located in the Luquillo Mountains, Puerto Rico. The plot had been mapped for historical land use, topography and soil type.

Key Results

Oeceoclades maculata was the most abundant of three orchid species surveyed and was found in all four historical cover classes. In cover class 3 (50–80 % forest cover in 1936), 192 of 343 plants were found at a density of 0·48 plants per 5 × 5 m subplot. Over 93 % of the 1200 subplots surveyed were composed of Zarzal or Cristal soil types, and O. maculata was nearly evenly distributed in both. The orchid was most common on relatively flat terrain. The distribution and abundance of two sympatric orchid species were negatively associated with that of the invasive species.

Conclusions

Oeceoclades maculata does penetrate ‘old growth’ forest but is most abundant in areas with moderate levels of past disturbance. Soil type makes little difference, but slope of terrain can be important. The negative association between O. maculata and native species may reflect differences in habitat requirements or a negative interaction perhaps at the mycorrhizal level.Key words: Oeceoclades maculata, Wullschlaegelia calcarata, Prescottia stachyodes, Orchidaceae, land-use history, tropical forest disturbance, terrestrial orchids, invasive species, Luquillo Experimental Forest, Puerto Rico, forest recovery, Caribbean     

Genetic rescue of an insular population of large mammals

Natural populations worldwide are increasingly fragmented by habitat loss. Isolation at small population size is thought to reduce individual and population fitness via inbreeding depression. However, little is known about the time-scale over which adverse genetic effects may develop in natural populations or the number and types of traits likely to be affected. The benefits of restoring gene flow to isolates are therefore also largely unknown. In contrast, the potential costs of migration (e.g. disease spread) are readily apparent. Management for ecological connectivity has therefore been controversial and sometimes avoided. Using pedigree and life-history data collected during 25 years of study, we evaluated genetic decline and rescue in a population of bighorn sheep founded by 12 individuals in 1922 and isolated at an average size of 42 animals for 10-12 generations. Immigration was restored experimentally, beginning in 1985. We detected marked improvements in reproduction, survival and five fitness-related traits among descendants of the 15 recent migrants. Trait values were increased by 23-257% in maximally outbred individuals. This is the first demonstration, to our knowledge, of increased male and female fitness attributable to outbreeding realized in a fully competitive natural setting. Our findings suggest that genetic principles deserve broader recognition as practical management tools with near-term consequences for large-mammal conservation.     

A gastropod from the tropical Atlantic becomes an established alien in the Mediterranean

We report the occurrence of an established population of the gastropod Mitrella psilla (Duclos, 1846), native on west African coasts of Mauritania, Senegal and Angola, on the shore of La Goulette, Bay of Tunis. The molluscan species of tropical West African affinity hitherto ascertained in the Mediterranean are not aliens, but have a native range which encompasses at least part of the Alboran Sea since historical times. Mitrella psilla appears therefore as the first instance of a mollusc with a tropical Atlantic origin being added to the Mediterranean fauna. The species was found near an important commercial harbour and is presumed to have been introduced by shipping.     

Genetic rescue of an endangered mammal by cross-species nuclear transfer using post-mortem somatic cells

Since the advent of procedures for cloning animals, conservation biologists have proposed using this technology to preserve endangered mammals. Here we report the successful cloning of a wild endangered animal, Ovis orientalis musimon, using oocytes collected from a closely related, domesticated species, Ovis aries. We injected enucleated sheep oocytes with granulosa cells collected from two female mouflons found dead in the pasture. Blastocyst-stage cloned embryos transferred into sheep foster mothers established two pregnancies, one of which produced an apparently normal mouflon. Our findings support the use of cloning for the expansion of critically endangered populations.     

Floral reward production is timed by an insect pollinator

Interval timing--sensitivity to elapsing durations--has recently been found to occur in an invertebrate pollinator, the bumble-bee (Bombus impatiens). Here, bumble-bees were required to time the interval between the start of foraging in a patch of low-quality artificial flowers providing 25% sucrose and the availability of a high-quality flower (HQF) that provided 50% sucrose after a fixed delay. The delay changed after every 20 foraging bouts in the order 30-150-30 s. Bees visited the HQF sooner when the delay was 30 s than when it was 150 s, and visits to the HQF peaked near the end of both delays. When the delay changed to 150 s, bees appeared to time both the previous 30 s delay and the new delay. To examine whether bees also learned what kind of reward was provided at the HQF, its usual reward was replaced with 25% sucrose in a final foraging bout. Bumble-bees rejected the HQF on the reward-replacement test. These results show that bumble-bees remembered both when reward was produced by the HQF and what type of reward was produced. These findings indicate that bumble-bees can learn both the timing and content of reward production.     

Challenges and trade-offs in the management of invasive alien trees

Over 430 alien tree species worldwide are known to be invasive, and the list is growing as more tree species are moved around the world and become established in novel environments. Alien trees can simultaneously bring many benefits and cause substantial environmental harm, very often leading to conflicts over how they should be managed. The impacts grow over time as invasions spread, and societal perceptions of the value of alien trees also change as understanding grows and as values shift. This leads to a dynamic environment in which trade-offs are required to maximise benefits and minimise harm. The management of alien tree populations needs to be strategic and adaptive, combining all possible management interventions to promote the sustainable delivery of optimal outcomes. We use examples, mainly from South Africa (where issues relating to invasive alien trees introduced for forestry have received most attention), to argue for holistic and collaborative approaches to alien tree management. Such approaches need to include bold steps, such as phasing out unsustainable plantation forestry that is based on highly invasive species, and in which the costs are externalised. Furthermore, it would be advisable to impose much stricter controls on the introduction of alien trees to new environments, so that problems that would arise from subsequent invasions can be avoided.     

Systematic bark morphology of some tropical trees

YUNUS, M., YUNUS, D & IQBAL, M., 1990. Systematic bark morphology of some tropical trees. Bark of 103 tropical trees of India has been examined from a systematic viewpoint and macroscopic features for use in field identification are considered. They are broadly categorized on the basis of diverse surface patterns and configurations as: deep fissured, shallow fissured, dippled, and entire. Identification of species is facilitated by the nature of the periderm and expansion tissue. The significance of bark anatomy in relation to systematics is discussed.     

Phenology of temperate trees in tropical climates

Several North American broad-leaved tree species range from the northern United States at 47°N to moist tropical montane forests in Mexico and Central America at 15–20°N. Along this gradient the average minimum temperatures of the coldest month (T_Jan), which characterize annual variation in temperature, increase from –10 to 12°C and tree phenology changes from deciduous to leaf-exchanging or evergreen in the southern range with a year-long growing season. Between 30 and 45°N, the time of bud break is highly correlated with T_Jan and bud break can be reliably predicted for the week in which mean minimum temperature rises to 7°C. Temperature-dependent deciduous phenology—and hence the validity of temperature-driven phenology models—terminates in southern North America near 30°N, where T_Jan>7°C enables growth of tropical trees and cultivation of frost-sensitive citrus fruits. In tropical climates most temperate broad-leaved species exchange old for new leaves within a few weeks in January-February, i.e., their phenology becomes similar to that of tropical leaf-exchanging species. Leaf buds of the southern ecotypes of these temperate species are therefore not winter-dormant and have no chilling requirement. As in many tropical trees, bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength. In tropical climates vegetative phenology is determined mainly by leaf longevity, seasonal variation in water stress and day length. As water stress during the dry season varies widely with soil water storage, climate-driven models cannot predict tree phenology in the tropics and tropical tree phenology does not constitute a useful indicator of global warming.     

Genetic vulnerability of a remnant ant population

Ants are ecologically important species in many environments forming a big proportion of the total animal biomass. However, their special features such as sociality and complementary sex-determination system have received little attention in conservation discussions. We examined the social and genetic structure of the hairy wood ant Formica lugubris in Ireland to evaluate factors relevant to the vulnerability of small, isolated wood ant populations. We also clarified the conservation status of the species in Ireland. Our results showed that the populations are mainly monogynous (one queen per nest). Consequently the effective population size is very low (<100 individuals) in Ireland. We found extremely little genetic variation, signs of inbreeding and inbreeding depression, which can be a consequence of the small effective population size and of the restricted gene flow due to strong isolation of populations. Putatively high genetic diversity at the sex-determining locus can reflect a larger population in the past. The study shows that even though the population may seem stable because of the long life span of queen ants, sociality can impact species conservation by keeping the effective population size small. According to our results, the hairy wood ant can be considered native to Ireland. Hence it needs urgent protection and the genetic issues need to be considered in the future management strategies.     

The influence of climatic seasonality on the diversity of different tropical pollinator groups

Tropical South America is rich in different groups of pollinators, but the biotic and abiotic factors determining the geographical distribution of their species richness are poorly understood. We analyzed the species richness of three groups of pollinators (bees and wasps, butterflies, hummingbirds) in six tropical forests in the Bolivian lowlands along a gradient of climatic seasonality and precipitation ranging from 410 mm to 6250 mm. At each site, we sampled the three pollinator groups and their food plants twice for 16 days in both the dry and rainy seasons. The richness of the pollinator groups was related to climatic factors by linear regressions. Differences in species numbers between pollinator groups were analyzed by Wilcoxon tests for matched pairs and the proportion in species numbers between pollinator groups by correlation analyses. Species richness of hummingbirds was most closely correlated to the continuous availability of food, that of bees and wasps to the number of food plant species and flowers, and that of butterflies to air temperature. Only the species number of butterflies differed significantly between seasons. We were not able to find shifts in the proportion of species numbers of the different groups of pollinators along the study gradient. Thus, we conclude that the diversity of pollinator guilds is determined by group-specific factors and that the constant proportions in species numbers of the different pollinator groups constitute a general pattern.     

Interelement relationships in leaves of tropical montane trees

Chemical concentrations in leaves are reported for 14 elements in 6 tree species of a montane rain forest in Sri Lanka. The plant taxa varied greatly in chemistry and a few taxa appeared to concentrate several elements in high amounts. The chemical variability among taxonomic units was examined by comparing element-by-element concentration ratios in leaves. Several species seemed to have typical patterns of concentration ratios for certain elements and the interelement relationships of different species seemed to be repeated across varying habitat conditions.     

Blind population genetics survey of tropical rainforest trees

Rainforest tree species can be difficult to identify outside of their period of reproduction. Vascular tissues from Carapa spp. individuals were collected during a short field trip in French Guiana and analysed in the laboratory with nuclear and chloroplast markers. Using a Bayesian approach, > 90% of the samples could be assigned to one of two distinct clusters corresponding to previously described species, making it possible to estimate the genetic structure of each species and to identify cases of introgression. We argue that this blind procedure represents a first-choice rather than a fallback option whenever related taxa are investigated.     

A reassessment of carbon content in tropical trees

Accurate knowledge of carbon (C) content in live wood is essential for quantifying tropical forest C stocks, yet generic assumptions (such as biomass consisting of 50% carbon on a weight/weight basis) remain widely used despite being supported by little chemical analysis. Empirical data from stem cores of 59 Panamanian rainforest tree species demonstrate that wood C content is highly variable among co-occurring species, with an average (47.4±2.51% S.D.) significantly lower than widely assumed values. Prior published values have neglected to account for volatile C content of tropical woods. By comparing freeze- and oven-dried wood samples, we show that volatile C is non-negligible, and excluding the volatile fraction underestimates wood C content by 2.48±1.28% (S.D.) on average. Wood C content varied substantially among species (from 41.9-51.6%), but was neither strongly phylogenetically conserved, nor correlated to ecological (i.e. wood density, maximum tree height) or demographic traits (i.e. relative growth rate, mortality rate). Overall, assuming generic C fractions in tropical wood overestimates forest C stocks by ～3.3-5.3%, a non-trivial margin of error leading to overestimates of 4.1-6.8 Mg C ha(-1) in a 50-ha forest dynamics plot on Barro Colorado Island, Panama. In addition to addressing other sources of error in tropical forest C accounting, such as uncertainties in allometric models and belowground biomass, compilation and use of species-specific C fractions for tropical tree species would substantially improve both local and global estimates of terrestrial C stocks and fluxes.