Native seed dispersal by rodents is negatively influenced by an invasive shrub

Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability of being eaten in situ than cached seeds, while the opposite occurred with animal–dispersed seeds. The latter were removed from the open woodland and edge habitats and cached under Rhododendron. This pattern was expected if predation risk was the main factor influencing the decision to eat or to cach a seed. Enhanced dispersal towards Rhododendron cover did not increase the prospects for seed survival, as density of hazel and oak saplings under its cover was close to zero as compared to open woodland, possibly due to increased cache pilferage or low seedling survival under dense shade, or both. Enhanced seed predation of ash and sycamore seeds close to Rhododendron cover also decreased recruitment of these trees. Rhododendron patches biased rodent foraging behaviour towards the negative (net predation) side of the conditional rodent / tree interaction. This effect will potentially impact native woodland regeneration and further facilitate Rhododendron spread due to refuge–mediated apparent competition.

Untangling the influence of biotic and abiotic factors on habitat selection by a tropical rodent

Understanding how animal populations respond to environmental factors is critical because large-scale environmental processes (e.g., habitat fragmentation, climate change) are impacting ecosystems at unprecedented rates. On an overgrazed floodplain in north-western Australia, a native rodent (Pale Field Rat, Rattus tunneyi) constructs its burrows primarily beneath an invasive tree (Chinee Apple, Ziziphus mauritiana) rather than native trees. The dense thorny foliage of the Chinee Apple may allow high rat densities either because of abiotic effects (shade, in a very hot environment) or biotic processes (protection from trampling and soil compaction by feral horses, and/or predation). To distinguish between these hypotheses, we manipulated Chinee Apple foliage to modify biotic factors (access to horses and predators) but not shade levels. We surveyed the rat population with Elliott traps under treatment and control trees and in the open woodland, in two seasons (the breeding season—January, and the nesting season—May). In the breeding season, we ran giving-up density experiments (GUD) with food trays, to assess the perceived risk of predation by rats across our three treatments. Selective trimming of foliage did not affect thermal regimes underneath the trees but did allow ingress of horses and we observed two collapsed burrows as a consequence (although long term impacts of horses were not measured). The perceived predation risk also increased (GUD values at food trays increased) and was highest in the open woodland. Our manipulation resulted in a shift in rat sex ratios (indicating female preference for breeding under control but not foliage-trimmed trees) and influenced rat behaviour (giving-up densities increased; large dominant males inhabited the control but not treatment trees). Our data suggest that the primary benefit of the Chinee Apple tree to native rodents lies in physical protection from predators and (potentially) feral horses, rather than in providing cooler microhabitat.

Ostracods, Charophytes, and Pollen from the Baynunah Formation

Ostracods, charophytes and pollen were retrieved from sediments of the Baynunah Formation. Autoecological characteristics of the ostracods and the charophytes, together with detailed observations on the taphonomy of ostracod valves, provide a reconstruction of the depositional environments of the Baynunah freshwater system. These microfossil assemblages indicate the presence of a large floodplain with a slow-flowing river with high suspended sediment load, as well as a system of shallow, possibly isolated, water bodies with clear waters and submerged meadows of macroalgae. The water bodies were characterized by fluctuating salinities that could be linked to phases of evaporation-desiccation and regeneration of the freshwater environment, i.e. alternation of humid and dry periods. Pollen remains indicate associations of herbaceous plants typical of open woodland to grassland habitats, with halophytes growing close to the water bodies.

Avifauna in Relation to Habitat Disturbance in Wildlife Management Areas of the Ruvuma Miombo Ecosystem, Southern Tanzania

Understanding of relative distribution of avifauna provides insights for the conservation and management of wildlife in the community managed areas. This study examined relative diversity, abundance, and distribution of avifauna in selected habitat types across five Wildlife Management Areas of the Ruvuma landscape in miombo vegetation, southern Tanzania. Five habitat types were surveyed during the study: farmland, swamps, riverine forest, dense and open woodland. Transect lines, mist-netting, and point count methods were used to document 156 species of birds in the study sites. Descriptive statistics and Kruskal-Wallis tests were used to compare species richness and diversity across habitat types. We found differences in avifaunal species distribution in the study area whereby farmland had the highest abundance of avifauna species and lowest in the riverine forest. These results suggest that variations of avifauna species abundance, diversity, and distribution could be attributed by human activities across habitat types; due to the reason that habitats with less human encroachment had good species diversity and richness. Therefore, to improve avitourism and avoid local extinction of species, we urge for prompt action to mitigate species loss by creating awareness in the adjacent community through conservation education on the importance of protecting such biodiversity resources.

Why Variation in Flower Color May Help Reproductive Success in the Endangered Australian Orchid Caladenia fulva

Caladenia fulva G.W. Carr (Tawny Spider-orchid) is a terrestrial Australian endangered orchid confined to contiguous reserves in open woodland in Victoria, Australia. Natural recruitment is poor and no confirmed pollinator has been observed in the last 30 years. Polymorphic variation in flower color complicates plans for artificial pollination, seed collection and ex situ propagation for augmentation or re-introduction. DNA sequencing showed that there was no distinction among color variants in the nuclear ribosomal internal transcribed spacer (ITS) region and the chloroplast trnT-trnF and matK regions. Also, authentic specimens of both C. fulva and Caladenia reticulata from the reserves clustered along with these variants, suggesting free interbreeding. Artificial cross-pollination in situ and assessment of seed viability further suggested that no fertility barriers existed among color variants. Natural fruit set was 15% of the population and was proportional to numbers of the different flower colors but varied with orchid patch within the population. Color modeling on spectral data suggested that a hymenopteran pollinator could discriminate visually among color variants. The similarity in fruiting success, however, suggests that flower color polymorphism may avoid pollinator habituation to specific non-rewarding flower colors. The retention of large brightly colored flowers suggests that C. fulva has maintained attractiveness to foraging insects rather than evolving to match a scarce unreliable hymenopteran sexual pollinator. These results suggest that C. fulva should be recognized as encompassing plants with these multiple flower colors, and artificial pollination should use all variants to conserve the biodiversity of the extant population.

Physico-Chemical Properties of Soil Under Acacia Senegal (L) Willd Plantation in Sahel Zone of Nigeria

BackgroundAcacia senegal (L) Wild known as gum Arabic tree, is a nitrogen fixing tree and a drought resistant species with potentials to improve infertile soils is planted in Sahel zone of Jigawa State, Nigeria for the production of gum arabic. However, there is dearth of information on the soil physico-chemical properties under plantation. MethodsSoil samples were collected from four 30 x 30m plots in the plantation and another plot in open woodland (control). In each plot, three replicate soil samples were taken from 0-15cm, 15-30cm and 30-60cm soil depths analyzed for micro and macronutrients, while soil acidity was determined both in water and 0.01M CaCl2.ResultsThe general soil texture of the plantation is loamy sand but with slight textural differentiation under the open woodland. Results indicated that physico-chemical properties of soils under the plantation were significantly different at P < 0.05 compared with the control. The mean soil bulk density ranged from 1.6g/cm3 in the plantation to 1.8g/cm3 in the open woodland. The high values of soil bulk density might be ascribed to loss of organic matter as a result of soil erosion and animal grazing which are common occurrences. ConclusionFrom the result of the study soil physico-chemical properties under the plantation are high and have more beneficial effects on the trees unlike the open woodland.

Euphorbia umbellata (African milk bush).

Euphorbia umbellata is a succulent shrub, widely cultivated as an ornamental. It grows in dry open woodland, rocky areas and also in disturbed habitats, where it has escaped from cultivation. Currently it is listed as invasive in India and Cuba, although there is no information available about its environmental impacts in either country. In Australia, it is listed as a minor environmental weed.