The effects of two parasitoids on the life history and metapopulation structure of the intertidal snail Littoraria filosa in different-sized patches of mangrove forest

We describe differences in life history of the intertidal arboreal snail, Littoraria filosa, among patches of mangroves ranging in size from isolated trees to large stands several square kilometres in area. Recruitment of L. filosa occurred from mid spring (October) to early winter (June), recruits grew rapidly and copulating adults were found during the following September–April. Populations within large patches of forest were annuals; all or most individuals died between October–January (spring–midsummer). In contrast, those in smaller peripheral patches were more likely to survive over the summer but survival differed among patches and years. These differences in life history were caused by a parasitoid fly (genus Sarcophaga) that attacked L. filosa 10 mm and longer and was present in all large patches, but absent from, or rare, in smaller peripheral patches. Experimental introductions to isolated trees confirmed that the fly could kill L. filosa. Another sarcophagid parasitoid that attacked L. filosa from 4 to less than 10 mm long was also found in every patch. The combined effects of these parasitoids appear to determine the metapopulation structure of L. filosa. Most adults in large patches were killed by the larger fly during early summer. Summer recruits were often killed by the smaller fly within a month of settlement and when this happened effective recruitment of L. filosa was reduced to autumn. The planktotrophic larval stage of L. filosa lasts less than 1 month, so the source of autumn recruits to all patches must have been adults that survived the early summer, most of which were in small patches or on isolated trees. Consequently these ”peripheral sources” are likely to be important for persistence of the metapopulation of L. filosa. The results of this study demonstrate that metapopulation structure may be determined by complex interactions and that common models cannot be assumed to apply in all habitats. Received: 15 September 1999 / Accepted: 31 January 2000     

Life history of the ghost shrimp, Callianassa japonica Ortmann (Decapoda: Thalassinidea), on an intertidal sandflat in western Kyushu, Japan

Growth, density, survival, and reproduction were examined for the population of the ghost shrimp, Callianassa japonica Ortmann, inhabiting an intertidal sandflat in western Kyushu, Japan, based on samples collected from May, 1989 to April, 1991. During the breeding season (June–October) each year, there were two discrete periods of egg production by females. The post-larval settlement, with a time-lag of 1–1.5 months (brooding plus larval developmental periods), generated two major recruitment cohorts, occurring in July–August (1st cohort) and September–November (2nd cohort). The higher growth rate of individuals after recruitment in the 1st cohort enhanced the separation of the two cohorts. Between sexes, the subsequent life history patterns and population characteristics were, for the most part, similar. In females, the majority of individuals of each of the two cohorts matured after approximately one year, respectively, at around a 20-mm total body length, and a portion of these cohorts survived as a fused cohort until June of the second year, breeding again prior to dying off by the end of September. The pattern of growth was an indeterminate type. For each of the two cohorts, the growth rates changed at two transition points of their life history, at around the beginning of their two breeding seasons. The growth rate for the 1st cohort slowed down at the first transition point, while that for the 2nd cohort speeded up there. This led to the approach and fusion of the two cohorts near the second transition point, when growth stopped. During periods other than the breeding seasons, high survival rates were exhibited by the two cohorts. During the first breeding season, a significantly low survival rate was observed for the 1st cohort, but not for the 2nd cohort. The degree of participation in breeding activity may be responsible for the above differences between cohorts. In the two male cohorts, while the cost of reproduction did not reduce the growth rates during the first breeding season, it lowered their survival rates more severely compared to those of females. This may be responsible for the slightly female-biased sex ratio in the population (1.06:1). The density of the population as a whole was stable throughout the study period, with the mean ± SD being 901 ± 157/m² (n = 27); the adult population declines during the breeding seasons were effectively replenished by recruitment each year.     

Gradation in Nutrient Composition and Photosynthetic Pathways Across the Restinga Vegetation of Brazil

The restinga comprises coastal vegetation formations which dominate the Atlantic seaboard of Brazil. Exposed sand ridges and associated lagoon systems have poorly developed soils subject to pronounced water deficits. Distinct vegetation zones support a high diversity of life forms, and a comparative study has been undertaken to investigate interactions between degree of exposure, nutrient supply and photosynthetic pathway (C₃, or CAM) in selected species across the restinga. A number of species occurring throughout the restinga were chosen as representative species of different life forms, comprising C₃ pioneer shrubs (Eugenia rotundifolia and Erythroxylum ovalifolium), impounding (tank) terrestrial bromeliad (Neoregelia cruenta: CAM) and the atmospheric epiphyte (Tillandsia stricta: CAM). Comparisons of plant and soil nutrient composition, and airborne deposition were conducted for each zone. Soil nutrient content and organic matter were closely related, reaching a maximum in zone 4, the seaward face of the inner dune. Salt concentration in leaves was independent of atmospheric deposition for the terrestrial species, in contrast to the atmospheric epiphyte T. stricta. In the slack area, vegetation formed characteristic “islands” with the soil beneath enriched in nutrients, suggesting a complex interplay between plants and soil during the development of vegetation succession. Here, two additional trees were investigated, C₃ and CAM members of the Clusiaceae, respectively Clusia lanceolata and C. fluminensis. Stable isotope composition of nitrogen (δ¹⁵N) was generally more negative (depleted in ¹⁵N) in plants with low total nitrogen content. This was exemplified by the atmospheric bromeliad, T. stricta, with an N content of 2.91 g/kg and δ¹⁵N of ?12.3 per mil. Stable isotopes of carbon (δ¹³C) were used to identify the distribution of photosynthetic pathways, and while the majority of bromeliads and orchids were CAM, analysis of the soil organic matter suggested that C₃ plants made the major contribution in each zone of the restinga. Since δ¹³C of plant material also suggested that water supply was optimal in zone 4, we conclude that succession and high diversity in the restinga is dependent on exposure, edaphic factors, and perhaps a critical mass of vegetation required to stabilize nutrient relations of the system.     

Ecology of Foliicolous Lichens at the “Botarrama” Trail (Costa Rica), a Neotropical Rain Forest. I. Species Composition and its Ecogeographical Implications1

A total of 217 species of typically foliicolous lichens were found at the “Botarrama” trail, a premontane rain forest in the Braulio Carrillo National Park, Costa Rica. The species composition confirmed the classification of this study sice as transitional between lowland wet and montane rain forest. In terms of species tichness, the foliicolous lichen flora was dominated by the families Gomphillaceae (Calenia, Echinoplaca, Gyalideopsis, and Tricharia), Trichotheliaceae (Porina and Tricbothelium), and Pilocarpaceae (Byssoloma and Fellhanera). The most frequent species were Porina mirabilis (including its supposed anamorph Phyllophiale alba), Gyalectidium filicinum, Porina rufula, and Strigula platypoda. A large proportion of the species was rare. Frequency distributions based on area cover corresponded well to general community models by closely fitting a log-normal approximation. Half of the species had narrow ecological amplitudes while more than 70 percent exhibited a wide geographical distribution, thus making che study site representative of a Neotropical rain forest. The use of foliicolous lichens as indicators of altitudinal zonation is discussed.     

REACTIVE OXYGEN PRODUCTION AND DAMAGE IN INTERTIDAL FUCUS SPP. (PHAEOPHYCEAE)

The research described in this paper was designed to test the hypothesis that the differential stress tolerance associated with the vertical zonation of intertidal seaweeds is attributable to reactive oxygen metabolism. To do so, we measured the production of, and damage caused by, reactive oxygen in three species of intertidal brown seaweeds— Fucus spiralis L., F. evanescens C. Ag., and F. distichus L.— that differ in their ability to withstand freezing, desiccation, and high light stress. Fucus spiralis is the most stress-tolerant species and F. distichus the least. Reactive oxygen production was determined by measuring the production of H₂O₂ and the oxidation of dichlorohydrofluorescein diacetate to dichlorofluorescein. Damage caused by freezing, desiccation, and high-light stress was assessed by measuring variable fluorescence (F_v/F_m) and lipid peroxidation. Production of reactive oxygen increased following freezing, desiccation, or high-light stress. In general, the data were consistent with the hypothesis that reactive oxygen metabolism is involved in stress tolerance. The production of reactive oxygen was relatively low in unstressed seaweeds, and there was little difference between species. Fucus distichus showed the greatest increase in reactive oxygen production after desiccation and freezing stress. Fucus evanescens produced more reactive oxygen production after desiccation than F. spiralis. Although F. evanescens and F. spiralis produced similar amounts of reactive oxygen after freezing, this treatment resulted in an increase in lipid peroxidation only in F. evanescens (and F. distichus ).     

Interspecific relationships and biogeography of some Bornean tree shrews (Tupaiidae: Tupaia), based on DNA hybridization and morphometric comparisons1

The interspecific relationships and biogeography of seven southeast Asian tree shrew species in the genus Tupaia were examined by DNA hybridization and multivariate morphometric analysis. Urogale everetti served as the outgroup. DNA hybridization data indicate that T. tana is most closely related to T. tnontana, and they form a clade with T. minor. Morphometric comparisons indicate that T. tana and 77 minor, and 7. montana and T palawanensis, form groups that, together, are most similar to T. glis. T. javanica and U. everetti cluster outside the rest of Tupaia. The DNA hybridization data support a model of Bornean speciation driven by sea‐level changes. They also indicate either (1) that there is a large variation in the rate of tree shrew evolution or (2) that U. everetti may in fact be a member of the ingroup. When considered in light of the phylogenetic results, the morphometric data suggest substantial convergence in body size or correlation in character changes.     

The role of macroinvertebrates for conservation of freshwater systems

Freshwater ecosystems are the most threatened ecosystems worldwide. Argentinian‐protected areas have been established mainly to protect vertebrates and plants in terrestrial ecosystems. In order to create a comprehensive biodiverse conservation plan, it is crucial to integrate both aquatic and terrestrial systems and to include macroinvertebrates. Here, we address this topic by proposing priority areas of conservation including invertebrates, aquatic ecosystems, and their connectivity and land uses. Location: Northwest of Argentina. We modeled the ecological niches of different taxa of macroinvertebrates such as Coleoptera, Ephemeroptera, Hemiptera, Megaloptera, Lepidoptera, Odonata, Plecoptera, Trichoptera, Acari, and Mollusca. Based on these models, we analyzed the contribution of currently established protected areas in the conservation of the aquatic biodiversity and we propose a spatial prioritization taking into account possible conflict regarding different land uses. Our analysis units were the real watersheds, to which were added longitudinal connectivity up and down the rivers. A total of 132 species were modeled in the priority area analyses. The analysis 1 showed that only an insignificant percentage of the macroinvertebrates distribution is within the protected areas in the North West of Argentina. The analyses 2 and 3 recovered similar values of protection for the macroinvertebrate species. The upper part of Bermejo, Salí‐Dulce, San Francisco, and the Upper part of Juramento basins were identified as priority areas of conservation. The aquatic ecosystems need special protection and 10% or even as much as 17% of land conservation is insufficient for species of macroinvertebrates. In turn the protected areas need to combine the aquatic and terrestrial systems and need to include macroinvertebrates as a key group to sustain the biodiversity. In many cases, the land uses are in conflict with the conservation of biodiversity; however, it is possible to apply the connectivity of the watersheds and create multiple‐use modules.     

Contrasting spatial heterogeneity of sessile organisms within mussel (Perna perna L.) beds in relation to topographic variability

We examined the spatial heterogeneity in three sessile rocky shore organisms, the mussel Perna perna, the barnacle Octomeris angulosa (Sowerby) and the red alga Gelidium pristoides (Turn.) at a range of continuous local scales along horizontal transects within mid- and upper mussel beds of South African shores. We also examined the relationships between variability of organisms and topographic features (rock depressions, slope, aspect), and between mussel, barnacle and algal variability over the same scales. To estimate spatial heterogeneity, we analyzed scaling properties of semivariograms using a fractal approach. Relationships between different variables at the different scales were examined by cross-semivariograms. Spatial dependence of P. perna variability increased with spatial dependence of topographic variability, so that scaling regions of mussel and topographic distributions corresponded well. This relationship often improved with larger local scales (mussel cover increased with depressions, steeper slope and aspect towards waves), while at smaller spatial scales, variability in mussel cover was less well explained by variability in topography. The variability of the barnacle O. angulosa exhibited spatial dependence, even on topographically unstructured shores. In contrast, the distribution of the alga G. pristoides revealed high fractal dimensions, showing spatial independence on topographically unstructured shores. Algae also showed a very strong negative relationship with mussels at most local scales, and a negative relationship with barnacles in upper zones, especially at larger local scales. Barnacles may show clear spatial dependence because of hydrodynamics (at larger local scales) and the need to find a future mate in close proximity (at smaller local scales), while algae may show a strong negative relationship with mussels because of competition for space.     

Population biology of the intertidal kelp, Alaria marginata Postels and Ruprecht: A non-fugitive annual

Persistence of annual plant populations requires sufficient seeds and suitable habitat for development and growth each year. Competition with perennials may prevent within site persistence and result in “fugitive” annual populations. Comparisons have been made between the population biology of annual macroalgae and terrestrial plants, but demographic information necessary to make strong comparisons is lacking for most of these algae, and life history differences may make such comparisons questionable. We studied population dynamics of the kelp Alaria marginata to determine if it was an annual and, if so, how populations persisted. This kelp is the dominant macroalga on exposed mid to low rocky intertidal shores along the Big Sur coast of California. Experimental clearings at two sites were used to assess recruitment timing and survivorship. Sporophytes were collected monthly to determine growth and fecundity. Recruitment occurred in late winter to early spring, primarily on geniculate corallines and residual A. marginata holdfasts. Thinning was inversely related to density, and occurred during the February through July growing season as larger thalli rapidly increased in length (up to 1.4 m month^− 1) and formed a thick canopy. Sorus development was positively related to size, began as early as March, peaked in late August-October, and decreased as adults were removed by winter surf. Spore release was generally highest (10⁸-10⁹ spores individual^− 11 h^− 1) between October and January and associated with high water motion. Survivorship of sporophytes beyond one year was < 1%, showing the populations were annual.Field observations and experiments on effects of canopy clearing, season of clearing, and influence of substrate type on recruitment were done to assess how these annual populations persist. Massive spore production at the onset of fall storms, survival of microscopic stages for 3-4 months facilitated by microhabitat refuges, rapid growth, large size and rapid maturation of sporophytes contributed to persistence. Furthermore, the dense stands with thick canopies may suppress potential competitors via shading and abrasion. Rather than being a fugitive, this combination of growth and life history features enables A. marginata and perhaps other large, annual kelps to maintain perennial populations.