Post-dispersal fate of Acacia seeds in an African savanna

African Acacia species are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. In Hluhluwe-iMfolozi Park, the numbers of adult Acacia nilotica (L.) Willd. Ex Del. subsp. kraussiana (Benth.) Brenan trees per hectare far exceed those of A. karroo Hayne adults. The relative dominance is reversed in the juvenile stage with A. karroo outnumbering A. nilotica threefold outside closed woodlands. We experimentally investigated the effects of location, structural habitat type, species, predator type and rodent presence on the level of post-dispersal seed predation in an attempt to explain species dominance in HluhluweiMfolozi Park. Post-dispersal predation of A. karroo seeds (21.8%) was higher than that of A. nilotica (12.7%). Predation levels depended on site, structural habitat type, level of protection from different predator types and rodent presence/absence. There was more rodent predation in tall grass areas (26.0%) than grazing lawn (10.7%) or canopy areas (15.2%), and most seeds (19.7%) were lost from unprotected control groups. Rodent presence was a significant factor in a model aiming to determine reasons for unexplained seed disappearance.Post-dispersal predation of seeds could not account for the differences in success between A. karroo and A. nilotica in Hluhluwe-iMfolozi Park

Alien plant species list and distribution for Camdeboo National Park, Eastern Cape Province, South Africa

Protected areas globally are threatened by the potential negative impacts that invasive alien plants pose, and Camdeboo National Park (CNP), South Africa, is no exception. Alien plants have been recorded in the CNP since 1981, before it was proclaimed a national park by South African National Parks in 2005. This is the first publication of a list of alien plants in and around the CNP. Distribution maps of some of the first recorded alien plant species are also presented and discussed. To date, 39 species of alien plants have been recorded, of which 13 are invasive and one is a transformer weed. The majority of alien plant species in the park are herbaceous (39%) and succulent (24%) species. The most widespread alien plant species in the CNP are Atriplex inflata (= A. lindleyi subsp. inflata), Salsola tragus (= S. australis) and cacti species, especially Opuntia ficus-indica. Eradication and control measures that have been used for specific problematic alien plant species are described

Road verges as invasion corridors? A spatial hierarchical test in an arid ecosystem

CITATION: Kalwij, J. M., Milton, S. J. & McGeoch, M. A. 2008. Road verges as invasion corridors? A spatial hierarchical test in an arid ecosystem. Landscape Ecology, 23: 439-451. doi:10.1007/s10980-008-9201-3The original publication is available at https://www.springer.com/journal/10980Disturbed habitats are often swiftly colonized by alien plant species. Human inhabited areas may act as sources from which such aliens disperse, while road verges have been suggested as corridors facilitating their dispersal. We therefore hypothesized that (i) houses and urban areas are propagule sources from which aliens disperse, and that (ii) road verges act as corridors for their dispersal. We sampled presence and cover of aliens in 20 plots (6 x 25 m) per road at 5-km intervals for four roads, nested within three localities around cities (n = 240). Plots consisted of three adjacent nested transects. Houses (n = 3349) were mapped within a 5-km radius from plots using topographical maps. Environmental processes as predictors of alien composition differed across spatial levels. At the broadest scale road-surface type, soil type, and competition from indigenous plants were the strongest predictors of alien composition. Within localities disturbance-related variables such as distance from dwellings and urban areas were associated with alien composition, but their effect differed between localities. Within roads, density and proximity of houses was related with higher alien species richness. Plot distance from urban areas, however, was not a significant predictor of alien richness or cover at any of the spatial levels, refuting the corridor hypothesis. Verges hosted but did not facilitate the spread of alien species. The scale dependence and multiplicity of mechanisms explaining alien plant communities found here highlight the importance of considering regional climatic gradients, landscape context and road-verge properties themselves when managing verges.DST-NRF Center of Excellence for Invasion Biology.Publisher’s versio

Interdisciplinary and multi-institutional higher learning : reflecting on a South African case study investigating complex and dynamic environmental challenges

Complex social-ecological problems need sustained interdisciplinary engagements across multiple disciplines, yet academic offerings continue to reflect disciplinary silos. To address this, a five-year program, within a developing country context, was conceived to follow an interdisciplinary research mode using a team of students and supervisors from various institutions across the disciplines of ecology, hydrology and economics. By using a flexible student training model, regional/ site specific knowledge was developed while simultaneously developing a shared vision and a model to combine information from each student project. Graduates felt enabled by the program that actively encouraged interdisciplinary interactions and engagements while simultaneously furthering disciplinary development. Cross disciplinary communication, was achieved through multiple engagement opportunities and common research outputs, all facilitated by an external boundary organization. While lengthy time frames are required for such collaborative interdisciplinary programs, researchers, higher learning institutions and funding agencies should not avoid this type of program and investment.The Water Research Commission of South Africahttp://www.journals.elsevier.com/current-opinion-in-environmental-sustainability2017-04-30hb2016Economic

Planet Hunters TESS. V. A Planetary System Around a Binary Star, Including a Mini-Neptune in the Habitable Zone

We report on the discovery and validation of a transiting long-period mini-Neptune orbiting a bright (V = 9.0 mag) G dwarf (TOI 4633; R = 1.05 R ⊙, M = 1.10 M ⊙). The planet was identified in data from the Transiting Exoplanet Survey Satellite by citizen scientists taking part in the Planet Hunters TESS project. Modelling of the transit events yields an orbital period of 271.9445 ± 0.0040 days and radius of 3.2 ± 0.20 R ⊕. The Earth-like orbital period and an incident flux of 1.56−0.16+0.20 F ⊕ places it in the optimistic habitable zone around the star. Doppler spectroscopy of the system allowed us to place an upper mass limit on the transiting planet and revealed a non-transiting planet candidate in the system with a period of 34.15 ± 0.15 days. Furthermore, the combination of archival data dating back to 1905 with new high angular resolution imaging revealed a stellar companion orbiting the primary star with an orbital period of around 230 yr and an eccentricity of about 0.9. The long period of the transiting planet, combined with the high eccentricity and close approach of the companion star makes this a valuable system for testing the formation and stability of planets in binary systems