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Fire is a natural feature of many ecosystems, with some vegetation types highly adapted to fire. However, very little is known about the effect of fire on spiders, especially as fires have become more frequent owing to human activity. We determine whether different spider functional guilds (web builders vs. wanderers) respond differently to fires in the sclerophyllous fynbos. We determine also the effect of rockiness as refuge for these guilds and whether it influences their post-fire recovery. There were three site categories of time-since-last fire: 3 months, 1 year, and 7 years. We found that fire caused a decline in spider richness and abundance, with the 3-month category supporting the lowest. In sites that were burned within 1 year, abundance of wanderers was as high as in sites that had 7 years to recover, whereas species richness and abundance of web builders in sites that were burned 1 year ago were as low as in recently burned sites. However, assemblages of wanderers differed among categories, while no differences were observed for web builders, highlighting that wanderers took longer time to recover than web builders. Species richness and abundance of both guilds were not affected by different levels of rockiness. However, rockiness is important in shaping assemblages of wanderers. The results emphasize that the assemblages of greatest conservation concern with increased fire frequencies are wanderers and are candidate surrogates for monitoring post-fire recovery. These results highlight the need to allow fynbos vegetation to recover fully between fire intervals and draws attention to the dangers of frequent unplanned fires. [ABSTRACT FROM AUTHOR]

Crown fire is a key selective pressure in Mediterranean-type plant communities. Adaptive responses to fire regimes involve trade-offs between investment for persistence (fire survival and resprouting) and reproduction (fire mortality, fast growth to reproductive maturity, and reseeding) as investments that enhance adult survival lower growth and reproductive rates. Southern hemisphere Mediterranean-type ecosystems are dominated by species with either endogenous regeneration from adult resprouting or fire-triggered seedling recruitment. Specifically, on nutrient-poor soils, these are either resprouting or reseeding life histories, with few intermediate forms, despite the fact that the transition between strategies is evolutionarily labile. How did this strong dichotomy evolve? We address this question by developing a stochastic demographic model to assess determinants of relative fitness of reseeders, resprouters and hypothetical intermediate forms. The model was parameterised using published demographic data from South African protea species and run over various relevant fire regime parameters facets. At intermediate fire return intervals, trade-offs between investment in growth versus fire resilience can cause fitness to peak at either of the extremes of the reseeder-resprouter continuum, especially when assuming realistic non-linear shapes for these trade-offs. Under these circumstances, the fitness landscape exhibits a saddle which could lead to disruptive selection. The fitness gradient between the peaks was shallow, which may explain why this life-history trait is phylogenetically labile. Resprouters had maximum fitness at shorter fire-return intervals than reseeders. The model suggests that a strong dichotomy in fire survival strategy depends on a non-linear trade-off between growth and fire persistence traits. [ABSTRACT FROM AUTHOR]

The significance of soil water redistribution by roots and nocturnal transpiration for nutrient acquisition were assessed for deep-rooted 3-year-old leguminous Aspalathus linearis shrubs of the Cape Floristic Region (South Africa). We hypothesised that hydraulic redistribution and nocturnal transpiration facilitate nutrient acquisition by releasing moisture in shallow soil to enable acquisition of shallow-soil nutrients during the summer drought periods and by driving water fluxes from deep to shallow soil powering mass-flow nutrient acquisition, respectively. A. linearis was supplied with sub-surface (1-m-deep) irrigation rates of 0, 2 or 4 L dayplant. Some plants were unfertilized, whilst others were surface- or deep-fertilized (1 m depth) with NaNO and CaP/FePO. We also supplied deuterium oxide (HO) at 1 m depth at dusk and measured its predawn redistribution to shallow soil and plant stems. Hydraulic redistribution of deep water was substantial across all treatments, accounting for 34-72 % of surface-soil predawn moisture. Fourteen days after fertilization, the surface-fertilized plants exhibited increased hydraulic redistribution and increased N and P acquisition with higher rates of deep-irrigation. Deep-fertilization also increased hydraulic redistribution to surface soils, although these plants additionally accumulated HO in their stem tissue overnight, probably due to nocturnal transpiration. Plants engaged in nocturnal transpiration also increased N and P acquisition from deep fertilizer sources. Thus, both nocturnal transpiration and hydraulic redistribution increased acquisition of shallow soil N and P, possibly through a combination of increased nutrient availability and mobility. [ABSTRACT FROM AUTHOR]

Previous studies in the fynbos biome of the Western Cape, South Africa, have suggested that biological decomposition rates in the fynbos vegetation type, on poor soils, may be so low that fire is the main factor contributing to litter breakdown and nutrient release. However, the fynbos biome also comprises vegetation types on more fertile soils, such as the renosterveld. The latter is defined by the shrub Elytropappus rhinocerotis, while the shrub Galenia africana may become dominant in overgrazed areas. We examined decomposition of litter of these two species and the geophyte Watsonia borbonica in patches of renosterveld in an agricultural landscape. In particular, we sought to understand how plant species identity affects litter decomposition rates, especially through variation in litter stoichiometry. Decomposition (organic matter mass loss) varied greatly among the species, and was related to litter N and P content. G. africana, with highest nutrient content , lost 65% of its original mass after 180 days, while E. rhinocerotis had lost ca. 30%, and the very nutrient poor W. borbonica <10%. Litter placed under G. africana decomposed slightly faster than when placed under E. rhinocerotis. Over the course of the experiment, G. africana and E. rhinocerotis lost N and P, while W. borbonica showed strong accumulation of these elements. Decomposition rates of G. africana and E. rhinocerotis were substantially higher than those previously reported from fynbos vegetation, and variation among the species investigated was considerable. Our results suggest that fire may not always be the main factor contributing to litter breakdown and nutrient release in the fynbos biome. Thus, biological decomposition has likely been underestimated and, along with small-scale variation in ecosystem processes, would repay further study. [ABSTRACT FROM AUTHOR]

The Cape Fynbos region of South Africa, a global biodiversity hotspot, hosted a diverse large mammal fauna till shortly after permanent European settlement (1652). How these animals survived in this exceptionally nutrient-poor environment is puzzling and it is generally believed that they restricted their movements to the more fertile shale areas. We tested the hypothesis that large herbivores avoid nutrient-poor limestone and sandstone fynbos shrublands in favour of shale-derived renosterveld vegetation using strontium (Sr) isotope analysis. If this technique could reconstruct the preferred feeding habitats of the contemporary fauna, it might also be useful for reconstructing the preferred feeding grounds of an extinct fauna. Using the assumption that small rodents have spatially restricted foraging activities, we determined the Sr/Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in the area. We then analysed Sr/Sr isotope ratios in the bones of a number of different large herbivores found in De Hoop Nature Reserve using laser ablation multi-collector inductively coupled plasma mass spectrometry. These values were compared to the bioavailable (rodent) values on the respective geological substrates. The technique identified differences in feeding substrate selection between different species and groups of the same species. The results also showed that shale renosterveld shrubland is not the exclusive source of nutrition for the large herbivores. Strikingly different isotope ratios among individuals in some populations pointed to significant dispersal events from distant sources. However, we were unable to pinpoint the exact feeding areas using Sr isotope analysis probably because some animals use a combination of substrates for feeding and because the geology of the study area is complex with graded isotope signals. We suggest that this technique is a valuable additional tool for exploring large mammal foraging behaviour on habitats associated with contrasting and less complex geology. [ABSTRACT FROM AUTHOR]

The Cape Floristic Region (CFR) is one of the most plant-species-rich regions in the world. It is also a warm temperate region and hypothetically should have high gall-insect species richness, making it interesting to investigate the relationship between the insects of the region and the rich flora. The relationship between gall-insect species richness (GSR) and plant richness was investigated for the Fynbos and for representatives of vegetation of the whole CFR. Samples (of up to 600 plants per transect for Fynbos) of woody shrubs were investigated for the presence of galls. The species richness of these insects was quantified, as well as plant species richness for each transect. GSR for Fynbos was compared to global figures for GSR. Fynbos harboured significantly more gall-insect species than other CFR vegetation types. GSR was positively correlated with CFR plant richness. GSR also closely tracked plant richness in Fynbos. GSR was not significantly influenced by other variables (elevation and aspect), suggesting that plant richness per se was an important factor in generating GSR. Fynbos GSR is comparable to other sclerophyllous regions of high GSR globally, corroborating that this vegetation type is conducive to gall-insect diversification. There is likely to be a high percentage of gall-insect endemism in the Fynbos, as might be expected from the high host fidelity of this insect group. [ABSTRACT FROM AUTHOR]

This study examines the impacts of woody, N-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the δN natural abundance technique. The results confirm earlier reports that invasion by woody shrubs results in organic matter and nutrient enrichment of surface soils of both ecosystems. However, patterns of nutrient availability (phosphorus and nitrogen) were not necessarily enhanced. In the more fertile strandveld both phosphorus and nitrogen (significant at P<0.10) showed trends towards enhanced annual mineralization rates upon invasion, while in the low nutrient fynbos system only phosphorus followed this trend. It is unclear whether this differential response is a consequence of plant- or soil-derived feedbacks on the decomposition processes in each system. The δN values of the soils from the invaded sites of both ecosystems indicated a strong influence of the alien species on the soil nitrogen component. However, as with other studies of natural ecosystems, the contribution of nitrogen from fixation could not be readily quantified with the δN natural abundance method because of problems in selecting suitable non-N-fixing reference plants. A technique of disrupting nodule structure and function, by fumigation with O, to obtain the δN value of a non-N-fixing speciment of the study species was tried and found to overcome some of the problems associated with the lack of suitable reference plants. With this technique it was possible to detect the almost total dependence of A. saligna on N-fixation in the fynbos soils with their low nitrogen mineralization rates. In the strandveld ecosystem with much higher soil nitrogen release rates A. cyclops was only partly dependent on fixation (about half) for its nitrogen. The nutrient enrichment of both ecosystems and trends towards enhanced rates of nutrient mineralization could have profound implications on the long-term success of alien invader clearing operations and the restoration of the indigenous flora at these sites. [ABSTRACT FROM AUTHOR]

Leucospermum conocarpodendron (L.) Buek (Proteaceae) seedlings were excavated several months after a fire in Cape fynbos. Seedlings under burnt parental skeletons had short hypocotyls (mean 25 mm) indicating passive dispersal whereas seedlings in the open were more deeply buried (mean 48 mm) by ants. Soil nutrient concentrations at the site of germination were negatively related to depth of burial and distance from parent. Ant dispersal resulted in seedlings emerging in soils with lower nutrient concentrations than passively dispersed seeds. Tissue analysis supported the soil results with lower P content in seedlings from open (ant dispersed) sites. Seedling survival in the first year of establishment was also lower in open sites, but not significantly so. However seedlings were slightly taller in the open. The results of this study, the first on naturally occurring intraspecific variation in myrmecochory, strongly contradict current explanations for the high incidence of myrmecochory in nutrient poor environments. [ABSTRACT FROM AUTHOR]

The annual growth pattern of male plants of the endemic, dioecious fynbos species, Thamnochortus punctatus, revealed sequential growth of the various below-and above-ground organs. Root and rhizome development were favoured in the wet winter months while culm elongation occurred in the warmer but drier spring to summer period. The reproductive phase of development followed in the hot dry summer and autumn. The asynchronous pattern of growth is suggested to enable the plant to maximize utilization of scarce resources within the confines of the environmental controls determined by the mediterranean-climate. Maximum root and rhizome activity in the rainy season enabled the plant to absorb and store nitrogen in mature culms for later above ground organ development. As the absorption of nitrogen from senscing material is essential for this pattern of organ development to assist in alleviating nutrient scarcity the high degree of nitrogen reabsorption, 35 to 70% for branches and culms respectively, shows the potential importance of asynchronous organ growth in overcoming nitrogen limitation of plant growth. Comparisons of dry mass and nitrogen allocation patterns indicate that developmental strategies employed by evergreen, perennial plants in climatically and edaphically constrained environments cannot be deduced from biomass allocation patterns alone as they do not appear to reflect strategies evolved to overcome nutrient limitation. [ABSTRACT FROM AUTHOR]