Enhancement of habitat heterogeneity and species richness on rocky shores inundated by sand

Summary Many rocky shores are subject to periodic inundation by sand, which is often thought to reduce species richness by eliminating organisms intolerant of sand scour or sand smothering. However, regular disturbance (e.g. inundation) should promote richness by preventing the development of low diversity climax communities. A study of faunal richness on 10 regularly inundated shores showed that inundation does promote richness, but by increasing habitat heterogeneity. Some species are excluded from parts of the shore by sand, but because of the patchiness of sand deposits they are rarely excluded from the entire shore. Other species are found only on rocks associated with sand, while typically sandy shore animals occur in the sand deposits themselves. Total richness (281 species) was greater than for local noninundated shores and sandy beaches combined.     

Seed dispersal spectra: a comparison of temperate plant communities

Abstract. We compare the dispersal spectra of diaspores from varied plant communities in Australia, New Zealand, and North America, assigning dispersal mode to each diaspore type on the basis of apparent morphological adaptations. Species with ballistic and external dispersal modes were uncommon in most communities we surveyed. Ant dispersal was also rather uncommon, except in some Australian sclerophyll vegetation types. The frequency of vertebrate dispersal ranged up to 60% of the flora, the highest frequencies occurring in New Zealand forests. Wind dispersal ranged as high as 70% of the flora, with the highest values in Alaska, but usually comprised 10–30% of the flora. Many species in most communities had diaspores with no special morphological device for dispersal. Physiognomically similar vegetation types indifferentbiogeographic regions usually had somewhat dissimilar dispersal spectra. The frequency of dispersal by vertebrates often increased and the frequency of species with no special dispersal device decreased along gradients of increasing vertical diversity of vegetation structure. Elevation and moisture gradients also exhibited shifts in dispersal spectra. Within Australia, vertebrate- and wind-dispersal increased in frequency along a soil-fertility gradient, and dispersal by ants and by no special device decreased. Habitat breadths (across plant communities) and microhabitat breadths (within communities) for species of each major dispersal type did not show consistent differences, in general. Ant-dispersed species often had lower cover-values than other species in several Australian vegetation types. We discuss the ecological bases of these differences in dispersal spectra in terms of the availability of dispersal agents, seed size, and other ecological constraints. Seed size is suggested to be one ecological factor that is probably of general relevance to the evolution of dispersal syndromes.     

Crustacean zooplankton species richness and associations in reservoirs and ponds of Aguascalientes State, Mexico

We report the species of crustacean zooplankton found in 19 resevoirs and ponds that were sampled at on at least two occasions in Aguascalientes State, Mexico, at a latitude of about 21°30 North Latitude. We collected a total of 33 cladoceran taxa, 15 calanoid and cyclopoid copepods, an Ergasilus copepod, 2 anostracans, one notostracan species and an amphipod. All these taxa had previously been reported in Mexico. As in more temperate areas, there was a significant correlation between the species richness and lake size. The species-area relationship for Aguascalientes was indistinguishable from that of more northerly lakes. The two most common associations of zooplankton species were (1) those small species that occurred with fish: Daphnia parvula, Diaphanosoma birgei, Leptodiaptomus siciloides, Mastigodiaptomus albuquerquensis, and Thermocyclops inversus, and (2) the large Daphnia schodleri that occurred with the predator Notonecta, in the absence of fish. With minor variations, these two associations also occur throughout temperate North America.     

A native nitrogen-fixing shrub facilitates weed invasion

Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.     

Habitat richness affects home range size in the red fox Vulpes vulpes

The spatial behaviour of the red fox Vulpes vulpes shows a great flexibility (Voigt and Macdonald, 1984). Home range size varies from 10 to over 5000 ha (Macdonald, 1987; Voigt, 1987). In carnivores, variations in home range size, weighed for body mass (Gittleman and Harvey, 1982), are largely related to differences in habitat productivity, but the intraspecific local variation in home range size can be only partially explained by differences in productivity. Macdonald (1981, 1983) suggested that home range size and configuration were determined in the red fox by the dispersion of food-rich patches. More recently, it has been found that

1.

(a) where humans are intolerant to the fox, resting sites are often located peripherally in home ranges (Meia and Weber, 1993);     

Species turnover between Afromontane and eastern African lowland faunas: patterns shown by amphibians

Abstract. Following the recognition of a discrete East African lowland amphibian fauna (Poynton, 1990), this paper investigates the possible recognition of an Afromontane amphibian fauna in southern Africa. Species turnover in a transect from the Mozambique/KwaZulu-Natal border area through Swaziland to the Eastern Transvaal highveld is described, and compared with previously described transects through Mozambique to Zimbabwe, and KwaZulu-Natal to the central Free State. Turnover in the Swaziland transect shows two peaks. Marked turnover at the edge of the interior plateau is taken to indicate an eastern border of an Afromontane fauna; the other peak, at the western edge of the coastal lowland, is taken to mark the border of an East African lowland fauna. A transition zone with a transitional assemblage occurs on the plateau slopes between the two borders. The Zimbabwean transect shows a similar pattern. The KwaZulu-Natal to Free State transect shows a broad transition from upland to lowland assemblages, which parallels the extensive intermingling of upland and lowland floristic elements in that area. A north-south turnover across the three transects shows northern species becoming progressively excluded from highland areas as they extend southwards, while southern species become limited to the highlands as they extend northwards. The cohesive north-south turnover pattern is consistent with the idea of a single Afromontane biogeographical unit, which can be related to a tropical East African lowland unit through a complex pattern of species turnover.     

Prairie plant guilds: a multivariate analysis of prairie species based on ecological and morphological traits

An ecomorphological analysis of the tallgrass prairie of central North America divided representative species of the native grassland flora into eight guilds or groups of species with similar life-form, phenology, and ecology. The guilds, segregated by multivariate analysis, are: (1) warm-season graminoids with Kranz anatomy and the Hatch-Slack photosynthetic pathway (C4 grasses); (2) cool-season graminoids without Kranz anatomy, but with the common Calvin or C3 photosynthetic pathway (C3 grasses and sedges); (3) annuals and biennial forbs; (4) ephemeral spring forbs; (5) spring forbs; (6) summer/fall forbs; (7) legumes; and (8) woody shrubs. The study was based on 158 plant species indigenous to three upland prairie sites in northeastern Kansas. Each species was scored for 32 traits which fall into five broad categories: plant habit, leaf characteristics, stem structures, root structures, and reproductive traits, including phenology. A multivariate, detrended correspondence analysis sorted the 158 species into the eight principal groups or guilds. These groups were further supported by a cluster analysis and discriminant function analysis of the same data set. The discriminant function analysis determined that 94.3% of the species were correctly classified in their respective guilds, and that the guilds were statistically different. Results indicate that guild analysis offers a basis for detailed classification of grassland vegetation that is more ecologically focused than species composition, as the myriad of species (about 1,000 prairie species on the central plains of North America) vary in presence, cover, and importance with their individualistic distribution.Abbreviations C3= C3 photosynthesis - C4= C4 photosynthesis - LSD= least significant difference     

A nested parasite species subset pattern in tropical fish: host as major determinant of parasite infracommunity structure

The number of monogenean gill parasite species associated with fish hosts of different sizes is evaluated for 35 host individuals of the West African cyprinid Labeo coubie. The length of host individuals explains 86% of the total variation in monogenean species richness among individuals. Larger hosts harbour more species than smaller ones. The existence of a hierarchical association of parasite species in individuals of L. coubie is demonstrated. Monogenean infracommunities on larger fish hosts consist of all species found on smaller hosts plus those restricted to the larger size categories, suggesting some degree of compositional persistence among host individuals. The findings provide strong support for an interpretation of the relationship between monogenean parasite species richness and host body size in terms of a nested species subset pattern, thus providing a new record of repetitive structure and predictability for parasite infracommunities of hosts.After 15/01/1995, ORSTOM, BP 165 97323 Cayenne cedex Guyane France     

The soil fauna: the other last biotic frontier

Different approaches to biodiversity yield global totals as small as 3 million or as large as 80 million species. Erwin's calculation and estimation leads to an estimate of ca 30 million species and relies on four assumptions of which one concerns the ratio between the number of canopy insects and those found elsewhere, especially in the soil. A short survey of the microarthropods living in coastal sand dunes and collected with a new flotation method yielded amazing results. In spite of the severity of the habitat (low organic matter content and extreme dryness), the density of microarthropods varied between 175 000 and 1 400 000 individuals per square metre, i.e., densities 3 to 10 times higher than densities usually observed in any other type of soil. A total of 31 species was recorded, most undescribed and smaller than 200 m. The consequences of these findings on the estimation of the number of species are discussed. It is suggested that the soil, including the deepest horizons and the rhizosphere, might constitute a huge reservoir for biodiversity.