Disturbances in semi-arid shrubland and arid grassland in the Karoo, South Africa: mammal diggings as germination sites

Mammals (mainly aardvark Orycteropus ufer , porcupine Hystrix austro-africanae , bat-eared fox Otocyon megalotis and Cape fox Vulpes chama ) which excavate holes in hard-capped soils in Karoo shrubland and inter-dune pans create microsites where seeds, detritus and water accumulate, and seeds germinate. Holes with seedlings were significantly deeper (6.7 ± 0.4 cm) than holes without seedlings (4.5 ± 0.3 cm). In open, inter-shrub sites, significantly more seedlings germinated in diggings than on the flat soil surface, but there was no difference in the proportion of seedlings germinating under shrubs and in diggings. In inter-dune pans, 96% of all seedlings found were growing in diggings.

Résumé

Les mammifères (surtout l'oryctérope Orycreropus afer , le porcépic Hystrix austro-ajricanae , l'otocyon Otocyion megalotis , et le renard du Cap Vulpes chama ) qui creusent des trous dans les régions buissonneuses du Karoo et dans les creux entre les dunes créent des microsites où les semences, les déchets et l'eau se rassemblent, et les semences germent. Les trous où elles germent sont significativement plus profonds (6,7 ± 0,4 cm) que ceux où elles ne germent pas (4,5± 0,3 cm). Aux endroits buissonneux ouverts, il pousse plus de jeunes plantes dans des creux qu'à la surface du sol, mais il n'y a pas de différence entre les proportions de celles qui poussent sous les buissons et dans les creux. Dans les creux entre les dunes, 96% des jeunes pousses croissent dans les excavations.     

Rampant drift in artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi)

Habitat fragmentation and its genetic consequences are a critically important issue in evaluating the evolutionary penalties of human habitat modification. Here, we examine the genetic structure and diversity in naturally subdivided and artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi), a small fish restricted to discrete coastal lagoons and estuaries in California, USA. We use five naturally fragmented coastal populations from a 300‐ km spatial scale as a standard to assess migration and drift relative to eight artificially fragmented bay populations from a 30‐ km spatial scale. Using nine microsatellite loci in 621 individuals, and a 522‐base fragment of mitochondrial DNA control region from 103 individuals, we found striking differences in the relative influences of migration and drift on genetic variation at these two scales. Overall, the artificially fragmented populations exhibited a consistent pattern of higher genetic differentiation and significantly lower genetic diversity relative to the naturally fragmented populations. Thus, even in a species characterized by habitat isolation and subdivision, further artificial fragmentation appears to result in substantial population genetic consequences and may not be sustainable.     

A new species of Ilex (Aquifoliaceae) from Espinhaço Range, Bahia, Brazil

A new species, Ilex mucugensis Groppo sp. nov. (Aquifoliaceae), is described and illustrated. The species is known only from 'campos rupestres' (vegetation of rock outcrops at high altitude) in the vicinity of Mucugê, Bahia State, Brazil, in the mountains of the Espinhaço Range. Comments on affinities, geographical distribution and phenology of the new species are also provided.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 153–156.     

Dieback and mortality of South African fynbos shrubs is likely driven by a novel pathogen and pathogen‐induced hydraulic failure

We examined whether extensive dry season dieback and mortality in a South African fynbos community were due to drought or pathogen attack. Plant dieback and mortality have been reported elsewhere in similar plant communities suggesting potential for a widespread climatic or biotic threat to this community. We collected tissue samples from Brunia noduliflora, the dominant plant in the community, and cultured them for potential plant pathogens. We also measured dry season predawn and midday water potentials of healthy and stressed plants and constructed pressure‐volume curves to assess turgor loss point. Plant stress and mortality were monitored over a 2‐year study period. Both healthy plants and plants that displayed moderate signs of stress had dry season predawn water potentials well above their turgor loss point suggesting plants were not water stressed. However, plants displaying >60% crown dieback had much lower water potentials (as low as ?12 MPa). A previously undescribed fungus (Pythium sp.) was isolated from the root vascular tissue of all stressed plants and was not present in healthy plants. The proximate cause of plant stress was likely pathogen‐induced, while the ultimate cause of plant death appears to be extreme water stress. The present study suggests that Brunia (Bruniceae), Leucadendron (Proteaceae) and Erica (Ericaceae), all emblematic and dominant genera within the diverse fynbos community, may be susceptible to Pythium infection. This may pose a serious threat to communities already threatened by climate change.