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Keystone Resource (keystone + resource)
Selected AbstractsSacoglottis gabonensis, a keystone fruit for forest elephants in the Réserve de Faune du Petit Loango, GabonAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009Bethan J. Morgan Abstract This study suggests that the fruits of Sacoglottis gabonensis (Baill.) Urb. (Humiriaceae) are a keystone resource for forest elephants (Loxodonta cyclotis Matschie) in a coastal rain forest, the Réserve de Faune du Petit Loango, Gabon (now part of Loango National Park). Faecal counts demonstrated that forest elephants used Sacoglottis -dominated forest more when Sacoglottis was abundant and electivity indices suggest that Sacoglottis is a preferred food. The flora of Petit Loango is characterized by the absence of herbaceous vegetation such as Marantaceae and Zingiberaceae, and during the prolonged dry season few fleshy fruits are present other than Sacoglottis fruits, which are produced in a glut during this time. While inter-annual fruiting reliability remains to be confirmed, fruit production in 1998 and high stem density relative to other study sites provide indirect evidence that Sacoglottis fruits are a reliable inter-annual resource at Petit Loango. It is thus proposed that Sacoglottis gabonensis fruits fulfil an important role as a keystone ,fallback' resource for forest elephants during the dry season at Petit Loango. Résumé Cet article suggère que les fruits de Sacoglottis gabonensis (Baill.) Urb. (Humiriaceae) sont une ressource primordiale pour l'éléphant de forêt (Loxodonta cyclotis Matschie) dans une forêt pluviale côtière, la Réserve de Faune du Petit Loango, au Gabon, qui fait partie du Parc National de Loango. Le comptage des excréments a montré que les éléphants de forêt fréquentent les forêts dominées par Sacoglottis davantage lorsque les Sacoglottis sont abondants, et les indices d'électivité suggèrent que c'est leur nourriture préférée. La flore de Petit Loango se caractérise par l'absence de végétation herbacée comme les Marantaceae et les Zingiberaceae, et pendant la longue saison sèche, il y a peu d'autres fruits pulpeux que les Sacoglottis qui sont produits en abondance à cette saison. Même s'il faut encore confirmer que les fruits sont produits en continu d'une année à l'autre, la production des fruits en 1998 et la densité de hautes pousses, comparées aux autres sites étudiés, montrent indirectement que les fruits de Sacoglottis sont une ressource fiable tout au long de l'année à Petit Loango. On pose donc l'hypothèse que les fruits de Sacoglottis gabonensis jouent un rôle important comme aliment ressource pour les éléphants de forêt de Petit Loango pendant la saison sèche. [source] The regulation of ecosystem functions by ecotypic variation in the dominant plant: a Spartina alterniflora salt-marsh case studyJOURNAL OF ECOLOGY, Issue 1 2002Denise M. Seliskar Summary 1Genetic differences among populations of a keystone species may affect ecosystem functional properties. We tested this by planting Spartina alterniflora from different geographical regions in a newly created salt marsh in Delaware, USA. 2Spartina alterniflora plants from morphologically distinct short-form (back marsh) populations were originally collected from Massachusetts (41°34, N), Delaware (38°47, N), and Georgia (31°25, N) in the USA and vegetatively propagated for 6 years in a salt water-irrigated common garden in Delaware before transfer to a newly created salt marsh. 3The magnitude of the expression of marsh functions in the created marsh, measured over 5 years, remained distinct in patches of each ecotype. End of season aerial biomass, below-ground biomass, root and rhizome distribution, canopy height, stem density, and carbohydrate reserves were closer to values reported for the plants' native sites than to those typical of Delaware. Thus, many of the plant features characteristic of particular latitudes appear to be under genetic control. Such ecotypic differentiation influences ecosystem function through keystone resource and keystone modifier activities. 4Respiration of the microbial community associated with either dead shoots or the soil varied with plant ecotype in the created wetland and the patterns reflected those reported for their native sites. High edaphic respiration under the Massachusetts ecotype was correlated with the high percentage of sugar in the rhizomes. Edaphic chlorophyll was greater under the canopies of the Massachusetts and Delaware ecotypes than under the Georgia canopy and exhibited a relationship similar to that of algal production rates reported for the native sites. Larval fish were most abundant in pit traps in the Massachusetts ecotype. [source] Giant Tortoises as Ecological Engineers: A Long-term Quasi-experiment in the Galápagos IslandsBIOTROPICA, Issue 2 2010James P. Gibbs ABSTRACT Giant tortoises were once a megafaunal element widespread in tropical and subtropical ecosystems. The role of giant tortoises as herbivores and seed dispersers, however, is poorly known. We evaluated tortoise impacts on Opuntia cactus (Cactaceae) in the Galápagos Islands, one of the last areas where giant tortoises remain extant, where the cactus is a keystone resource for many animals. We contrasted cactus populations immediately inside and outside natural habitats where tortoises had been held captive for several decades. Through browsing primarily and trampling secondarily tortoises strongly reduced densities of small (0.5,1.5 m high) cacti, especially near adult cacti, and thereby reduced densities of cacti in larger size classes. Tortoises also caused a shift from vegetative to sexual modes of reproduction in cacti. We conclude that giant tortoises promote a sparse and scattered distribution in Opuntia cactus and its associated biota in the Galápagos Islands. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] Fig-eating by vertebrate frugivores: a global reviewBIOLOGICAL REVIEWS, Issue 4 2001MIKE SHANAHAN ABSTRACT The consumption of figs (the fruit of Ficus spp.; Moraceae) by vertebrates is reviewed using data from the literature, unpublished accounts and new field data from Borneo and Hong Kong. Records of frugivory from over 75 countries are presented for 260 Ficus species (approximately 30% of described species). Explanations are presented for geographical and taxonomic gaps in the otherwise extensive literature. In addition to a small number of reptiles and fishes, 1274 bird and mammal species in 523 genera and 92 families are known to eat figs. In terms of the number of species and genera of fig-eaters and the number of fig species eaten we identify the avian families interacting most with Ficus to be Columbidae, Psittacidae, Pycnonotidae, Bucerotidae, Sturnidae and Lybiidae. Among mammals, the major fig-eating families are Pteropodidae, Cercopithecidae, Sciuridae, Phyllostomidae and Cebidae. We assess the role these and other frugivores play in Ficus seed dispersal and identify fig-specialists. In most, but not all, cases fig specialists provide effective seed dispersal services to the Ficus species on which they feed. The diversity of fig-eaters is explained with respect to fig design and nutrient content, phenology of fig ripening and the diversity of fig presentation. Whilst at a gross level there exists considerable overlap between birds, arboreal mammals and fruit bats with regard to the fig species they consume, closer analysis, based on evidence from across the tropics, suggests that discrete guilds of Ficus species differentially attract subsets of sympatric frugivore communities. This dispersal guild structure is determined by interspecific differences in fig design and presentation. Throughout our examination of the fig-frugivore interaction we consider phylogenetic factors and make comparisons between large-scale biogeographical regions. Our dataset supports previous claims that Ficus is the most important plant genus for tropical frugivores. We explore the concept of figs as keystone resources and suggest criteria for future investigations of their dietary importance. Finally, fully referenced lists of frugivores recorded at each Ficus species and of Ficus species in the diet of each frugivore are presented as online appendices. In situations where ecological information is incomplete or its retrieval is impractical, this valuable resource will assist conservationists in evaluating the role of figs or their frugivores in tropical forest sites. [source] | ||||||||||