Max Edkins

Bio: Max Edkins is an academic researcher from University of Cape Town. The author has contributed to research in topics: Feed-in tariff & Allopatric speciation. The author has an hindex of 6, co-authored 7 publications receiving 340 citations.

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic, abbreviated and direct development

Abstract: The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.

Baobabs and elephants in Kruger National Park: nowhere to hide

Abstract: Baobab size class distributions were surveyed in the Limpopo National Park (LNP), Mozambique, and the Kruger National Park (KNP), South Africa. There are very few elephants in the LNP and the baobab population there had a reverse J-shaped size class distribution with many small baobabs. In contrast, the elephant-impacted baobab population of KNP displayed a mono-modal size-class distribution, with a lack in recruitment. Within KNP, elephant impact (percentage bark stripped up to the height of 3 m) decreased with increasing rockiness and slope steepness. We interpret this to suggest that steep rocky slopes are inaccessible to elephants and therefore these sites may act as a refuge for baobabs. In such inaccessible areas, the baobab population has a similar size-class distribution to that of the populations in the LNP. However, these baobab refugia are restricted in the northern KNP landscape and are therefore probably not large enough to sustain a viable baobab population.

Morphological and genetic analyses suggest that southern African crown crabs, Hymenosoma orbiculare , represent five distinct species

Abstract: The crown crab, Hymenosoma orbiculare, occurs all along the coast of southern Africa and displays great morphological variation across this range. To determine whether the species comprises several distinct taxonomic units, H. orbiculare were collected from 18 estuaries and lagoons between Walvis Bay in Namibia and Kosi Bay in north-eastern South Africa. Open ocean individuals were also obtained from False Bay in south-western South Africa. Morphological and genetic (using mitochondrial DNA) comparisons were carried out between individuals from all locations. Five monophyletic clusters were identified on the basis of genetic data, each confined to specific portions of the distribution range. Morphological data supported the distinctness of each of these clusters. The typical H. orbiculare, characterized by large size (maximum carapace width 28 mm) and absence of the characteristic ornamentations of other morphotypes, occurred in estuaries and lagoons all along the west and south coasts. False Bay deep-water individuals were of two forms. The first small, granulose, and setose morph appears to represent the previously synonymized species, H. geometricum, and is distinguished by a long rostrum, a raised setaceous gastric region on the carapace, and post-branchial projections. The second False Bay form represents a new, undescribed species, identified primarily by genetic characters. Estuarine forms from the southeast and east coast formed two more clusters, distinguished by their small size (carapace width <10 mm), relatively large eyes, long walking legs, projections on the abdomen, and small anterior spikes on the coxae of the legs. Specimens from south-eastern sites differed from more northern samples by their longer second walking legs and darker colour. We propose that South African crown crabs in fact represent five distinct species: the true H. orbiculare, the form previously described as H. geometricum (to be re-established as a valid species), and three new species that remain to be formally described. Die Kronenkrabbe, Hymenosoma orbiculare, kommt uberall entlang der Kuste des sudlichen Afrikas vor und zeichnet sich in diesem Verbreitungsgebiet durch betrachtliche morphologische Variation aus. Um festzustellen, ob es sich bei der Art um verschiedene taxonomische Einheiten handeln konnte, wurden Proben von H. orbiculare in 18 Flussmundungen und Lagunen zwischen Walvis Bay in Namibia und Kosi Bay im nordostlichen Sudafrika gesammelt sowie in tieferem Wasser der False Bay im Sudwesten von Sudafrika. Die Tiere der verschiedenen Fundstellen wurden sowohl morphologisch als auch genetisch (mitochondriale DNS) miteinander verglichen. Mit Hilfe der genetischen Analyse konnten funf monophyletische Einheiten identifiziert werden, jede davon beschrankt auf einen bestimmten Bereich des Verbreitungsgebietes der Art. Dieses Resultat wird durch morphologische Unterschiede unterstutzt. Die eigentliche H. orbiculare wurde in Flussmundungen und Lagunen der West- und Sudkuste gefunden. Sie lasst sich von anderen Morphotypen durch Grosse (maximale Carapaxweite 28 mm) und Fehlen einiger fur andere Morphotypen typischer Ornamentierungen unterscheiden. Zwei Morphotypen wurden in tieferem Wasser der False Bay gefunden. Der erste davon ist kleiner, granuloser und beborsteter und scheint die fruher einmal synonymisierte Art H. geometricum zu reprasentieren. Diese unterscheidet sich von anderen Kronenkrabben der False Bay durch ein langeres Rostrum, eine beborstete Vorwolbung der gastrischen Region des Carapax und post-branchiale Vorsprunge. Der zweite Morphotyp aus der False Bay stellt eine neue, noch unbeschriebene Art dar, deren Eigenstandigkeit hauptsachlich auf genetischen Daten beruht. Die in den Flussmundungen der Sudost- und Ostkuste vorkommenden Kronenkrabben reprasentieren zwei weitere Morphotypen, die sich durch ihre geringe Korpergrosse (Carapaxweite <10 mm), die relative Grosse der Augen, die Lange der Schreitbeine, durch Vorsprunge auf dem Pleon und kleine anteriore Dornen auf den Coxae der Beine auszeichnen. Individuen der Sudostkuste unterscheiden sich von weiter nordlich vorkommenden Krabben durch ihr langeres zweites Beinpaar und ihre dunklere Farbung. Wir sind der Meinung, dass es sich bei den sudafrikanischen Kronenkrabben um funf eigenstandige Arten handelt: die eigentliche Art H. orbiculare, die Art, die vormalig als H. geometricum beschrieben wurde (und als eigene Art wieder etabliert werden sollte), sowie drei weitere Arten, die noch beschrieben werden mussen.

The Political Economy of Energy Transitions: The Case of South Africa

Abstract: This paper explores the political economy of energy transition in South Africa. An economic model based around a powerful ‘minerals-energy complex’ that has previously been able to provide domestic and foreign capital with cheap and plentiful coal-generated electricity is no longer economically or environmentally sustainable. The paper analyses the struggle over competing energy visions, infrastructures and political agendas in order to generate insights into the governance and financing of clean energy transitions in South Africa. It provides both a rich empirical account of key policy developments aimed at enabling such a transition and provides reflections on how best to theorise the contested politics of energy transitions.

Savanna woody plant dynamics: the role of fire and herbivory, separately and synergistically

Abstract: Althoughthedemographyofwoodyplantsinsavannashaslongbeenshowntobeduetomanyfactors,therestill is no consensus as to the relative importance of the top-down processes of fire and herbivory, nor on how fire and herbivory affect plant demography. We review the recent literature and suggest that further progress depends on the following: (i) a demographic framework with clear terminology and which focuses on recruitment, transitions and mortality, (ii) an understandingofmechanismsofhow fireactuallydamagesplantsandhowplantssurviveandout-growthisdamage,mainly throughheight,barkthicknessordiametergrowth,(iii)anunderstandingofhowlossesinbiomassduetoherbivorymayaffect plant demography and, (iv) a consideration of interactions between fire and herbivory. Our synthesis suggests (i) strong recruitment limitation as well as some evidence of transition limitation by both fire and herbivory, (ii) that in some cases herbivory alone, notably by elephants and impala, can be more significant than fire alone, on woody plant population size, (iii) that fire and herbivory together are a lethal combination for woody plants and, (iv) that differences in strategies and responses of savanna plants to fire and herbivory are poorly explored.

The estuaries of South Africa

Abstract: 1. Fifteen years on! One hundred and fifty years on! B. R. Allanson and D. Baird 2. Geomorphology and sedimentology J. A. G. Cooper, C. I. Wright and T. R. Mason 3. Estuarine hydrodynamics E. H. Schumann, J. L. Largier and J. H. Slinger 4. Chemistry B. R. Allanson and D. Winter 5. Primary producers J. B. Adams, G. C. Bate and M. O'Callaghan 6. Mangroves T. D. Steinke 7. Estuarine zooplankton T. Wooldridge 8. Estuarine macro invertebrates C. J. De Villiers, A. N. Hodgson and A. T. Forbes 9. The Ichthyofauna A. K. Whitfield and J. F. K. Marais 10. Estuarine birds P. A. R. Hockey and J. K. Turpie 11. Estuaries as ecosystems D. Baird 12. Man and management P. D. Morant and N. W. Quinn 13. Perspectives B. R. Allanson, D. Baird and A. E. F Heydorn Index.