Granitic Rock Outcrops Research Articles

Structural analysis of the vegetation on a highland granitic rock outcrop in Southeast Brazil

Granitic rock outcrops of the Brazilian southeast are either coastal or inland. The latter can often have high altitudes, such as in the summits of do Mar and da Mantiqueira, where they are known as Campos de Altitude. The landscape on these high altitude plateaux is often a mosaic of shrubs and treelets within a bunchgrass matrix, with sparse pteridophytes and other herbs, interspersed with variable extensions of rock outcrops. Despite the pervasiveness of rock outcrops in the Brazilian landscape, studies on the structural analysis of the vegetation on such formations are scarce. This study aimed to analyze the structure of the vegetation on a highland granitic rock outcrop in Parque Estadual da Serra do Brigadeiro, state of Minas Gerais, Southeast Brazil (42°20' - 42°40' S and 20°20' - 21°00' W, 1,722 m of elevation ). Quantitative parameters of absolute and relative frequency and dominance (cover) were estimated. The group analysis used the Jaccard similarity index. Trilepis lhotzkiana, Panicum sp. 1, and Vellozia variegata presented the highest relative frequencies, relative dominances and importance values. These three species, along with Dyckia bracteata, Rhynchospora emaciate, and Tibouchina cf. manicata, represented 98.3% of the relative dominance. The remaining 1.7% referred to 22 remaining species. The distinction among quadrats within formed groups by cluster analysis was due to the great number of low frequency species.

Population differentiation and species cohesion in two closely related plants adapted to neotropical high‐altitude ‘inselbergs’,Alcantarea imperialisandAlcantarea geniculata(Bromeliaceae)

Isolated granitic rock outcrops or 'inselbergs' may provide a window into the molecular ecology and genetics of continental radiations under simplified conditions, in analogy to the use of oceanic islands in studies of species radiations. Patterns of variability and gene flow in inselberg species have never been thoroughly evaluated in comparison to related taxa with more continuous distribution ranges, or to other species in the same kingdom in general. We use nuclear microsatellites to study population differentiation and gene flow in two diploid, perennial plants adapted to high-altitude neotropical inselbergs, Alcantarea imperialis and Alcantarea geniculata (Bromeliaceae). Population differentiation is pronounced in both taxa, especially in A. imperialis. Gene flow in this species is considerably lower than expected from the literature on plants in general and Bromeliaceae in particular, and too low to prevent differentiation due to drift (N(e)m < 1), unless selection coefficients/effect sizes of favourable alleles are great enough to maintain species cohesion. Low gene flow in A. imperialis indicates that the ability of pollinating bats to promote gene exchange between inselbergs is smaller than previously assumed. Population subdivision in one inselberg population of A. imperialis appears to be associated with the presence of two colour morphs that differ in the coloration of rosettes and bracts. Our results indicate a high potential for inselbergs as venues for studies of the molecular ecology and genetics of continental radiations, such as the one that gave rise to the extraordinary diversity of adaptive strategies and phenotypes seen in Bromeliaceae.

The vegetation of granite rock outcrops in Rio de Janeiro, Brazil, and the need for its protection

Rock outcrop communities usually receive very little attention from scientists and environmentalists. We examined the vegetation occurring in eight gneiss-granite rock outcrops at Rio de Janeiro State (Brazilian Atlantic coast) which exists in natural associations on soil islands. A total of 86 vascular plant species, belonging to 30 families, was found on 347 soil islands. Bromeliaceae, Asteraceae and Velloziaceae species were the most frequent plants, many of them endemic to these habitats. Ordination and cluster analyses using species frequency on each site made evident some major distinctions related to local influences, most probably the proximity to the sea. Each outcrop presented high values of the Shannon-Wiener index of species diversity. Species richness was very dependent on the total area, and high beta diversity was observed amongst sites. Similarities with the South American and African rock-outcrop communities were found. Despite their uniqueness as habitats, their possession of several endemic species and the fragility of the ecosystem involved, Brazilian rock outcrops are not protected by specific environmental legislation and we propose urgent actions for their protection.

Orthotrichum shevockii (Orthotrichaceae), a New Moss Species from the Southern Sierra, California

Orthotrichum shevockii from dry granitic boulders in the southern Sierra of California is described as a new species belonging to subgen. Pulchella (Schimp.) Vitt sect. Diaphana Vent. It grows in small, dark green to blackish tufts and is characterized by having highly papillose leaf cells, bito tristratose leaf margins, immersed to shortly emergent capsules, double peristomes without prostomes, with 8 exostome teeth, and 8 or 16 endostome segments, and strongly hairy calyptra with papillose hairs. During field work in the southern Sierra in some of the driest desert areas of southern California a small, dark green to blackish Orthotrichum was collected from granitic rock outcrops. Even with a hand-lens the moss looked quite distinct and different from any North American Orthotrichum species described so far. The assumption that is was something new was further supported by microscopical studies, which for example revealed the bito tristratose leaf margins, a rare character state within the genus. Among the North American species completely or partially bistratose leaves are known from Orthotrichum strangulatum P. Beauv., O. cupulatum Brid., O. hallii Sull. & Lesq., and O. pellucidum Lindb., all members of subgen. Orthotrichum, and from O. bolanderi Sull. from subgen. Phaneroporum Delogn. The species from subgen. Orthotrichum all have erect or spreading dry exostome teeth and thus differ from the plants from the southern Sierra having the dry teeth clearly reflexed. Orthotrichum bolanderi, a species found in the dry, mountainous regions of western and central California, has the dry exostome teeth reflexed-recurved, but differs in having superficial stomata, completely bistratose leaves in the upper 23, and subsheathing leaf bases. The new species was first collected by James Shevock, phanerogamic taxonomist extraordinaire, who is opening the eyes of the junior author to the bryophyte riches of the southern Sierra in California, and is named in his honor. ORTHOTRICHUM SHEVOCKII Lewinsky-Haapasaari & Norris, sp. nov. FIGS. 1-23 O. alpestri affine, sed fuscantius et minus, papillis foliorum minoribus, capsulis profunde immersis, foliis aliquantum rigidis margines bivel tristriatos habentibus. Clos ly related to O. alpestre B.S.G., but darker and smaller, with deeply immersed to emergent capsules and rather rigid leaves with bito tristratose margins. TYPE: U.S.A. CALIFORNIA. Kern Co., along California hig way 178, 1.12 km east of Chimney Peak Road, north base of Scodie Mountains, 1,150 m, Shevock 13072 (holotype, UBC; isotypes ALTA, KUO). U.S.A. CALIFORNIA. Kern Co., off the Pacific Crest Trail about 3.6 km south of Walker Pass to fork of Jack Creek, Kiavah Wilderness, Scodie Mountains, 1,600 m, Shevock 13398, 13404 (paratypes, ALTA, KUO, UBC). Plants erect in small dark green to blackish tufts, to 1.5 cm high. Leaves spreading when moist, when dry rather rigidly erect. Leaves to 5 mm long, about 4:1, ligulate-lanceolate to elliptic-lanceolate, broadest near the middle, with obtuse to rounded acute apices. Median laminal cells isodiametric with rounded lumens, thick-walled with strong corner thickenings, to 16 psm wide, high pluri-papillose with papillar salients simple to forked, extending to 14 as high as the leaf thickness. Basal juxtamarginal cells short rectangular, 1.2-2:1, pellucid and thinwalled with corner thickenings, to 16 pm wide. Basal juxtacostal cells pellucid and short rectangular, 1.5-3:1, to 18 pLm wide with lateral walls straight but mostly with corner thickenings. Abaxial cells of costa base rectangular, 2-4:1, with forked papillae mostly restricted to the distal and proximal cell ends. Margins recurved from above the base to near the apex, mostly papillose-crenate. Costa ending within 5-10 cells of apex, distally placed in welldefined keel, in transverse section homogeneous, at mid-leaf 3-4 cells thick with about 4-5 cells on abaxial perimeter. Abaxial and adaxial cells of costa si ilar to the adjacent laminal cells. Axillary hairs to 5 cells and 150 pxm long, of essentially uniform 0007-2745/98/435-438$0.55/0 This content downloaded from 207.46.13.25 on Mon, 12 Sep 2016 04:47:32 UTC All use subject to http://about.jstor.org/terms 436 THE BRYOLOGIST [VOL. 101

Mammifères, taille et climat:Les faunes “locales” de mammifères sont-elles au plan de la taille une collection d'espèces prises au hasard dans l'intervalle souris-éléphant ou sont-elles des communautés structurées par le milieu?

Characteristic plant assemblages of rock outcrops were recorded in Northern Western Chats and Konkan region of Maharashtra. Twenty-one endemic species were restricted in distribution to specific rocky habitats. The vegetation has close phytogeographic affinities with natural herbaceous vegetation on granitic rock outcrops and ferricretes in Africa.

Biodiversity and vegetation of small‐sized inselbergs in a West African rain forest (Taı, Ivory Coast)

The vegetation of small granitic rock outcrops (geomorphologically small‐sized inselbergs) which do not reach the canopy was studied in the Taı rain forest (southwestern Ivory Coast) under aspects of species diversity and phytogeographical affinities. Rock outcrops form edaphically arid (due to absent or very sparse soil cover) and microclimatologically xeric (i.e. low air humidity, temperature regularly exceeding 50°C) islands with cryptogamic crusts, succulents and poikilohydric vascular plants as characteristic elements of their vegetation which differs totally from the surrounding forest. Altogether sixty‐six species of vascular plants out of twenty‐nine families occur, the number of species correlates positively with inselberg size. Compared with large inselbergs the microclimatic attributes of small‐sized rock outcrops are less pronounced. This is accompanied by a decrease of typical inselberg taxa (i.e. species mainly occurring on inselbergs). Low beta diversity between inselbergs indicates deterministic influences as important regulators of species composition. Annual Poaceae and Cyperaceae are richly represented. It can be hypothesized that inselbergs may represent natural growing sites of widely distributed tropical weeds today. Inselbergs might provide habitat resources for savanna elements in rain forest zones.

Ecology of isolated open-formation Tropidurus (Reptilia: Tropiduridae) in Amazonian lowland rain forest

Ecological, morphological, and life-history characteristics of three as yet undescribed populations of open-formation Tropidurus species in Rondônia and a population of Tropidurus oreadicus in Pará, Brazil, that are isolated on rock outcrops completely surrounded by lowland tropical forest were compared with similar characteristics of a eurytopic open-formation close relative, Tropidurus hispidus, and a crevice-adapted close relative, Tropidurus semitaeniatus, from an open-formation (caatinga) habitat in northeastern Brazil. Individuals of the isolated Amazonian populations do not enter the forest, but escape into narrow crevices on rock outcrops when disturbed. They are restricted to the only habitat patch in tropical forest similar to open-formation habitats, granitic rock outcrops. The outcrops maintain cerrado and caatinga vegetation and published paleoecological data indicate that the forested area surrounding the outcrops in Rondônia was cerrado in the recent past. Individuals in the isolated Tropidurus populations are morphologically flattened compared with T. hispidis, clutch size is reduced, and relative clutch mass is reduced, as is observed in other crevice-adapted species of lizards. Females deposit eggs under granitic cap rocks, like the flattened lizard T. semitaeniatus. The most parsimonious explanation for the set of characteristics shared by these four isolated lizard populations is that natural selection has led to an adjustment of behavior, morphology, and certain life-history characteristics in response to the high ecological risks associated with entering surrounding forest. It remains unclear whether this occurred once (which assumes a common ancestor), followed by canalizing selection, or the populations converged independently on similar morphology and ecology (which assumes different ancestors). The direction of divergence in behavior, morphology, clutch size, relative clutch mass, and nesting behavior in isolated populations of Tropidurus species remains unknown.

Distribution and Genetic Structure of Two Allopatric Beetle (Coleoptera: Melyridae) Species on Rock Outcrops in the Southeast

This study compares the population genetic structure of two spatially subdivided species that differ in the average distance separating their populations. Collops georgianus Fall and C. tricolor Say are allopatrically distributed on granitic rock outcrops of the southeastern United States. C. georgianus is distributed on a dense cluster of outcrops in northcentral Georgia, and C. tricolor is found on outcrops farther apart to the east, north, and west. Populations within the ranges of each species were analyzed using protein electrophoresis. The more geographically isolated species ( C. tricolor ) is genetically more diverse, with a significantly higher average within-species genetic distance. Its populations tend to be fixed, or nearly so, for alternate alleles and contain more alleles per locus. C. tricolor is more highly substructured, its FST value (0.485) being higher than those generally reported for other spatially subdivided species. A Mantel analysis showed the genetic distances between populations to be related more to their contiguity than to the geographic distances between them.

MACRO- AND MICROGEOGRAPHIC STRUCTURE OF A SPATIALLY SUBDIVIDED BEETLE SPECIES IN NATURE.

Spatial subdivision of species can affect their population structure by allowing processes such as limited dispersal, spatial heterogeneity in selective pressures, small population sizes, and random events to operate. By studying species restricted to islands or "island" habitats, one can attempt to determine which of these factors have affected the current structure of the population. Collops georgianus (Coleoptera: Melyridae), a beetle species endemic to the "island" habitat of granitic rock outcrops, was chosen to see how its spatially subdivided distribution has affected its genetic structure. Its genetic structure was examined on both a macrogeographic and a microgeographic level using protein electrophoresis. Macrogeographically, 12 populations throughout its range were sampled. The discontinuous distribution of outcrops, and thus populations, throughout its range, has determined the connectivity of the populations. Significant variation in allele frequencies and substructuring (FST = 0.192) was found throughout the range, but there was no spatial autocorrelation. Microgeographically, in the central part of the range, where outcrops are denser and more continuously distributed in space, there was evidence of isolation by distance. Very little variation in allele frequencies was found, but a low but significant level of substructuring occurred among the populations. Comparison of disjunct and continuous populations microgeographically revealed no effect of disjunct distributions, although a significant effect of distance was detected. Effective population size variation among populations and between years, compounded with the effects of local extinctions, suggest that random processes such as drift and founder effects are important determinants of the population's genetic structure.

Evidence of Plant Succession on Granite Outcrops of the Georgia Piedmont

Successional changes are taking place in the vegetation of certain on granitic rock outcrops in the Lithonia, Georgia, area (Piedmont Plateau). The floristic composition and maximum soil depths of 34 communities, first studied in 1957, were re-examined in 1968 and 1976-1978. Maximum soil depth tended to increase over time. Sixteen of the 34 communities studied showed successional changes in floristic composition, confirming the earlier hypothesis that lichen-annual, annual-perennial and herb-shrub communities represent seral stages as soil depth increases. There are characteristic plants and maximum soil depths for each stage, with overlapping depth ranges. Diamorpha communities, which occur on the shallowest soils, have remained unchanged floristically and maximum soil depths have changed only slightly. With 1-12 cm increases in soil depths, three lichen-annual communities became annual-perennial communities, four annual-perennial communities progressed to an herb-shrub or shrub-tree stage, and one herb-shrub community became a shrubtree community. Shrub-tree communities may represent an edaphic climax subject to periodic regression to earlier seral stages. INTRODUCTION Plant communities on exposed granitic rock to the E and SE of Atlanta, Georgia, and the life histories of characteristic species of these communities have been the subject of scientific study for many years. McVaugh (1943) included the portion of the Piedmont near Atlanta in his comprehensive study of the vegetation of granitic flatrocks in the southeastern United States and suggested two types of succession on rock surfaces, mat formation and succession in soil-filled depressions in the exposed rock. In 1964, Burbanck and Platt published an analysis of the vegetation of 40 communities of plants located on three geologically similar granite outcrops. The communities were termed since each occurred on soil in depressions surrounded by exposed rock. These communities were classified into four types based on maximum soil depth and type of vegetation in each community. Burbanck and Platt suggested that the four types of communities represented seral stages related to the edaphic conditions; the greater the soil depth, the more advanced was the seral stage. Since the original observations were made in 1957, 1958 and 1959, the communities have been examined periodically and data collected pertaining to depth of soil and floristic changes to determine whether or not plant succession is taking place and whether the four types of communities represent seral stages. This paper presents some of the results of a 22-year study of communities on three different granite outcrops in the Georgia Piedmont near the town of Lithonia, SE of Atlanta, Georgia. MATERIALS AND METHODS Burbanck and Platt (1964) selected 40 communities for study in 1957: 17 on Arabia Mountain, 16 on Rock Chapel Mountain and seven on Mount Rollaway. These communities occurred in irregularly circular or elliptic depressions in exposed rock surfaces, ranged from 1.3 to 56.9 m2 in area but usually had a diam of 5 m or less, and the depth of soil ranged from 2-50 cm at the deepest part of each island community. Communities were chosen which had intact bottoms; that is, there was no evidence of cracks or crevices in the rock beneath the community. Four types of communities were recognized by Burbanck and Platt (1964) based on characteristic vegetation and maximum soil depth: diamorpha (a succulent annual) (2-9 cm); lichen-annual herb (7-15 cm); annual-perennial herb (14-39 cm); herb-shrub

Distribution and Trends of Discordant Ages of the Plutonic Rocks of Northeastern Washington and Northern Idaho

K-Ar dating of granitic rocks in northeastern Washington and northern Idaho indicates four distinct periods of intrusion at about 200+ m.y., 170 m.y., 93 to 101 m.y., and 45 to 51 m.y. The two oldest events are each represented by only one pluton in the region. Plutons of the 93- to 101-m.y. event are numerous in the eastern and western parts of the region and may have occupied much of the intervening area before the youngest event. Except for a group of unrooted plutons in the upper plate of a thrust fault, no plutonic rocks between the west edge of the Pend Oreille River valley and the Purcell Trench south of lat 48° 15′ N. yielded an age outside the 45- to 51-m.y. bracket. Westward from the Pend Oreille River valley, the plutonic rocks yield successively older ages over a zone 8 to 25 km wide. All coexisting mineral pairs from rocks within this zone yield discordant ages. West of the zone, mineral pairs yield concordant ages in the 93- to 101-m.y. range. The apparent ages were contoured over about 15,000 km 2 , and the position and trend of discordant ages have been delineated. East of the Purcell Trench, a partly preserved mirror image of the Pend Oreille River zone of discordance is disrupted by faults in the trench and in places appears to have been removed. In the vicinity of the Purcell Trench, the apparent ages suggest a complex thermal history probably complicated by faults concealed in the trench. The apparent ages can be contoured at least two different ways, one interpretation assuming that the contours are disrupted by a large fault or fault system in the trench, the other assuming either that no faults exist or that the faults predate the 45 to 51 m.y. intrusions. The contours can also be drawn either being offset by the Hope fault or crossing the fault without interruption. The distribution of granitic rock outcrops around the Purcell Trench and Hope fault is such that a unique solution cannot be determined for either area.

Numerical Densities of Algal Cells and Growth in the Lichen Genus Cladonia

This study relates population density patterns of the phycobiont Trebouxia throughout the mycobiont during different seasons in very similar species of Cladonia that occupy granitic rock outcrops. Algal cells were most abundant near the tips of the thalli; they were most abundant also on the S and W sides of each mound-like clump of thalli; and they were more abundant within the clump in May than in February. Densities of the phycobiont in each of three species of Cladonia were essentially similar at the same places in the thalli and in the same seasons, and densities decreased with distance from the edges of the clumps.