ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

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Biogeography of prostrate-leaved geophytes in semi-arid South Africa: hypotheses on functionality (1999)

Esler, Karen J. ; Rundel, Phillip W. ; Vorster, Piet

Springer

Plant ecology 142 (1999), S. 105-120

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ISSN: 1573-5052

Keywords: Amaryllidaceae ; Biogeography ; Geophylly ; Leaf Orientation ; Succulent Karoo

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Nowhere is the species diversity of geophytes greater than in the five mediterranean-climate ecosystems of the world. Of these, the Cape mediterranean zone of South Africa is the most speciose. While the relative diversity and importance of geophytes of all of the other four mediterranean regions of the world drops off sharply as one moves into adjacent winter-rainfall desert regions, geophytes in the semi-arid to arid Succulent Karoo (including Namaqualand) remain a very important component of the flora, both in terms of abundance and diversity (comprising 13 to 29% of the regional floras in this region). Apart from species richness, there are also a number of interesting geophyte growth forms in this region. One unusual growth form is geophytes with flattened leaves that lie prostrate on the soil surface. At least eight families (Amaryllidaceae, Colchicaceae, Eriospermaceae, Geraniaceae, Hyacinthaceae, Iridaceae, Orchidaceae and Oxalidaceae) exhibit this growth form. While this growth form is relatively common in many geophyte lineages in the Succulent Karoo biome and the Cape mediterranean zone (Fynbos biome), and occurs infrequently through the summer-rainfall temperate regions of Africa, it is virtually absent in other regions worldwide. A null hypothesis is that the prostrate leaved trait is a neutral characteristic, however biogeographical data do not support this. A neutral trait would be unlikely to show such a clear pattern of distribution. Several alternative hypotheses on the adaptive significance of this growth form are discussed. These include: avoidance of herbivory, reduction in competition from neighbors, creation of a CO2 enriched environment below the leaves, reduction of water loss around the roots, reduction of water loss through transpiration, precipitation of dew on the leaves and maintenance of optimal leaf temperatures for growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1009822311708

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Comparative patterns of phenology and growth form diversity in two winter rainfall deserts: the Succulent Karoo and Mojave Desert ecosystems (1999)

Esler, Karen J. ; Rundel, Philip W.

Springer

Plant ecology 142 (1999), S. 97-104

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ISSN: 1573-5052

Keywords: Convergent evolution ; Desert annual ; Leaf succulent ; Namaqualand ; Rooting depth

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract A comparative study of community structure and seasonal growth dynamics in the arid winter rainfall regions of the Succulent Karoo in South Africa and the Mojave Desert of the United States suggests that remarkably divergent patterns of resource use and resultant growth form diversity exist in regions with outwardly similar climatic regimes. An understanding of these divergent patterns in the two winter rainfall deserts allows predictions to be made on vegetation response to global change. Above-ground plant growth in the Succulent Karoo begins with the first significant rains in late summer and continues through winter because moderate minimum temperatures allow continued growth. These communities have low structural diversity above-ground, but also below-ground, where root systems commonly do not exceed 20 cm in depth. These shallow root systems harvest water from upper soil horizons soon after rain falls, and growth declines as rainfall decreases in late spring. In contrast, low temperatures during winter inhibit growth in the Mojave Desert until early spring at a time when a mean 74% of the hydrologic year precipitation (July-June) has already occurred. Thus species in this structurally diverse system rely on deeper stores of water for growth in spring and early summer. A global change scenario of a 2 to 4 °C increase in mean annual temperature and increased summer rainfall in the Mojave desert would be expected to produce similar conditions in the Mojave Desert to those that exist in the Succulent Karoo today. Assuming no genetic constraints on phenotypic plasticity, this would suggest increased species diversity and a decline in structural diversity in the Mojave Desert over evolutionary time. Increased summer rainfall in the Succulent Karoo would be expected to lead to invasions of grasses and thus increased competitive pressure reducing community diversity.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1009830513525

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Ecological and phylogenetic patterns of carbon isotope discrimination in the winter-rainfall flora of the Richtersveld, South Africa (1999)

Rundel, Philip W. ; Esler, Karen J. ; Cowling, Richard M.

Springer

Plant ecology 142 (1999), S. 133-148

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ISSN: 1573-5052

Keywords: Crassulacean acid metabolism ; Mesembryanthema ; Aizoaceae ; Succulent Karoo ; Succulent leaves

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Leaf tissues of vascular plant species from the arid Richtersveld of northern Namaqualand (Succulent Karoo), South Africa, show a great range of variation in carbon isotope discrimination. Analyses of Δ values for species with obligate C3 metabolism demonstrated that the water use efficiency indicated by these values varies between species and within a species population both between seedlings and mature shrubs and between sites along an aridity gradient. An expected pattern of increasing water use efficiency with greater longevity in these species was not present, however. Only among ephemerals were there taxa with high Δ values associated with low water use efficiency, but these high values were balanced by other ephemeral species with low Δ values comparable to those typical of moderate to long-lived shrubs. The extent to which putative CAM species in the succulent flora rely entirely on nocturnal carbon fixation is highly variable. Species of Crassulaceae and Aloe (Asphodelaceae) relied almost exclusively on CAM photosynthesis, although Crassulaceae from more mesic environments may be CAM-flexible. Succulent-leaved species of Senecio and leaves of stem-succulent Euphorbia were CAM-flexible in their Δ values, while shrubby species of Ceraria (Portulacaceae) appeared to rely primarily on C3 photosynthesis. Variable patterns of reliance on CAM photosynthesis were present in the ecologically dominant Mesembryanthema of the Aizoaceae. Shrubby species of the subfamily Mesembryanthemoideae, although capable of CAM-flexibility in less xeric habitats, relied largely on CAM fixation of carbon in our field sites. Within the subfamily Ruschioideae, there was a wide range of Δ values indicating species with CAM, CAM flexibility, and primary reliance on C3 photosynthesis. Low Δ values indicative of typical CAM fixation were associated with species with greater longevity, suggesting that a positive correlation may exist between the degree of reliance on CAM photosynthesis and plant life span.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1009878429455

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A preliminary study of the responsiveness to seasonal atmospheric and rainfall patterns of wash woodland species in the arid Richtersveld (1999)

Wand, Stephanie J.E. ; Esler, Karen J. ; Rundel, Philip W. ; [et al.]

Springer

Plant ecology 142 (1999), S. 141-160

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ISSN: 1573-5052

Keywords: Photosynthesis ; Phreatophyte ; Stable carbon isotope composition ; Water relations ; Winter rainfall desert

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Seasonal carbon and water relations were compared among seven tree or shrub wash woodland species in the winter rainfall desert of the Richtersveld National Park, South Africa. Plants were generally aseasonal with respect to gas exchange, but responsive to rainfall events with respect to water relations and phenology. Relatively narrow annual ranges in potential evapotranspiration due to the maritime influence could explain why these plants respond more to fluctuations in water acquisition potential than to evaporative demand. Two species were summer-deciduous, but one of them (Ozoroa concolor) responded to aseasonal summer rainfall by leafing out and flowering. These two species had high shoot xylem water potentials when in leaf. All other species were sclerophyllous evergreens with low water potentials, particularly the shallow-rooted shrub Zygophyllum prismatocarpum, and Boscia albitrunca which may have a different rooting pattern to the other phreatophytes. The latter species was also unique due to its high leaf nitrogen contents, photosynthetic rates and stomatal conductances, despite very low leaf water potentials. Leaf stable carbon isotope composition C13δC) varied between species (−22 to −27‰), but was lower than the mean for arid regions worldwide. The values indicated moderately high levels of water use efficiency, but a less conservative strategy in two species, including Boscia albitrunca. The affinities of these species to summer rainfall biomes, their apparent decline in the western arid regions in recent geological history following aridification, and their absence southwards in the winter rainfall regions, suggest that these wash species rely on sporadic summer rainfall events to some extent. They may be at risk if predicted increases in temperature and changes in rainfall patterns alter their effective moisture availability.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1009882530364

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5

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Live fast, die young: estimating size-age relations and mortality pattern of shrubs species in the semi-arid Karoo, South Africa (2000)

Wiegand, Thorsten ; Milton, Suzanne J. ; Esler, Karen J. ; [et al.]

Springer

Plant ecology 150 (2000), S. 115-131

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ISSN: 1573-5052

Keywords: Growth models ; Karoo ; Mortality ; Size-age relation ; Shrub community

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We present a technique for estimating size-age relations and size-dependent mortality patterns of long-lived plants. The technique requires two sets of size data of individual (non-marked) plants that should be collected with a time-lag of several years in the same area of a study site. The basic idea of our technique is to assume general (three parameter) families of size-dependent functions which describe growth and mortality that occurred between the two data gathering events. We apply these growth and mortality functions to the size data of the early data set and construct predicted size-class distributions to compare it, in a systematic way, to the size-class distribution of the later data set. In a next step we calculate the size-age relations from the resulting growth functions, which yield the smallest difference between observed and predicted size-class distribution. Applying this technique to size data of five dominant shrub species at the Tierberg study site in the semiarid Karoo, South Africa produced new insight into the biology of these species which otherwise cannot be obtained without frequent measurements of marked plants. We could relate characteristics of growth behavior and mortality, for certain subgroups of the five species, to the life-history attributes evergreen vs. deciduous, succulent vs. woody, and early reproductive vs. late reproductive. The results of our pilot-study suggest a broad applicability of our technique to other shrublands of the world. This requires at least one older record of (individual) shrub-size data and performance of resampling.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1026526419886

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The impact of anthropogenically induced degradation on the vegetation and biochemistry of South African palmiet wetlands (2018)

Rebelo, Alanna J. ; Emsens, Willem-Jan ; Meire, Patrick ; [et al.]

Springer

In: Wetlands Ecology and Management. 2018; 26(6): 1157-1171. Published 2018 Nov 02. doi: 10.1007/s11273-018-9638-3.

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Publication Date: 2018-11-02

Print ISSN: 0923-4861

Electronic ISSN: 1572-9834

Topics: Biology

Published by Springer

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Mismatches between demographic niches and geographic distributions are strongest in poorly dispersed and highly persistent plant species (2020)

Pagel, Jörn ; Treurnicht, Martina ; Bond, William J. ; [et al.]

National Academy of Sciences

In: PNAS - Proceedings of the National Academy of Sciences of the United States of America. 2020; 117(7): 3663-3669. Published 2020 Feb 06. doi: 10.1073/pnas.1908684117.

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Publication Date: 2020-02-06

Description: The ecological niche of a species describes the variation in population growth rates along environmental gradients that drives geographic range dynamics. Niches are thus central for understanding and forecasting species’ geographic distributions. However, theory predicts that migration limitation, source–sink dynamics, and time-lagged local extinction can cause mismatches between niches and geographic distributions. It is still unclear how relevant these niche–distribution mismatches are for biodiversity dynamics and how they depend on species life-history traits. This is mainly due to a lack of the comprehensive, range-wide demographic data needed to directly infer ecological niches for multiple species. Here we quantify niches from extensive demographic measurements along environmental gradients across the geographic ranges of 26 plant species (Proteaceae; South Africa). We then test whether life history explains variation in species’ niches and niche–distribution mismatches. Niches are generally wider for species with high seed dispersal or persistence abilities. Life-history traits also explain the considerable interspecific variation in niche–distribution mismatches: poorer dispersers are absent from larger parts of their potential geographic ranges, whereas species with higher persistence ability more frequently occupy environments outside their ecological niche. Our study thus identifies major demographic and functional determinants of species’ niches and geographic distributions. It highlights that the inference of ecological niches from geographical distributions is most problematic for poorly dispersed and highly persistent species. We conclude that the direct quantification of ecological niches from demographic responses to environmental variation is a crucial step toward a better predictive understanding of biodiversity dynamics under environmental change.

Print ISSN: 0027-8424

Electronic ISSN: 1091-6490

Topics: Biology , Medicine , Natural Sciences in General