Too close for comfort: spatial patterns in acorn barnacle populations

Spatial patterns in aggregations form as a result of the interplay between costs and benefits experienced by individuals. Such self-organisation of aggregations can be explained using a zonal model in which a short-range zone of repulsion and longer-range zone of attraction surrounding individuals leads to emergent pattern properties. The signal of these processes can be detected using spatial pattern analyses. Furthermore, in sessile organisms, post-settlement mortality reveals the relative costs and benefits of positions within the aggregation. Acorn barnacles are known to require contact with conspecifics for reproduction and are therefore believed to aggregate for this purpose; isolated individuals may also be more susceptible to abiotic stress and predation. At short distances, however, competition for space and resources is likely to occur. In this study spatial patterns of barnacles (Semibalanus balanoides L.) were analysed using pair-correlation functions. Individuals were dispersed at distances below 0.30 cm, but peak relative density occurred at a distance of 0.36 cm from conspecifics. This is much closer than required for reproductive access, implying a strong aggregative drive, up to the point of physical contact with neighbours. Nevertheless, analysis of dead barnacles illustrated that such proximity carries a cost as barnacles with many neighbours were more likely to have died. The inferences obtained from these patterns are that barnacles aggregate as closely as they can, and that local neighbourhood competition is a powerful determinant of mortality. These processes give rise to the observed pattern properties

Geochemical and mineralogical indicators for aqueous processes in the Columbia Hills of Gusev crater, Mars

Water played a major role in the formation and alteration of rocks and soils in the Columbia Hills. The extent of alteration ranges from moderate to extensive. Five distinct rock compositional classes were identified; the order for degree of alteration is Watchtower = Clovis >Wishstone = Peace > Backstay. The rover’s wheels uncovered one unusual soil (Paso Robles) that is the most S-rich material encountered. Clovis class rocks have compositions similar to Gusev plains soil but with higher Mg, Cl, and Br and lower Ca and Zn; Watchtower and Wishstone classes have high Al, Ti, and P and low Cr and Ni; Peace has high Mg and S and low Al, Na, and K; Backstay basalts have high Na and K compared to plains Adirondack basalts; and Paso Robles soil has high S and P. Some rocks are corundum-normative, indicating that their primary compositions were changed by loss and/or gain of rock-forming elements. Clovis materials consist of magnetite, nanophase ferric-oxides (npOx), hematite, goethite, Ca-phosphates, Ca- and Mg-sulfates, pyroxene, and secondary aluminosilicates. Wishstone and Watchtower rocks consist of Fe-oxides/oxyhydroxides, ilmenite, Ca-phosphate, pyroxene, feldspar, Mg-sulfates, and secondary aluminosilicates. Peace consists of magnetite, npOx, Mg- and Ca-sulfates, pyroxene, olivine, feldspar, apatite, halides, and secondary aluminosilicates. Paso Robles consists of Fe3+-, Mg-, Ca-, and other sulfates, Ca-phosphates, hematite, halite, allophane, and amorphous silica. Columbia Hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks, volcaniclastic materials, and/or impact ejecta by solutions that were rich in acid-volatile elements

Population, resources, and environment: Implications of human behavioral ecology for conservation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43481/1/11111_2005_Article_BF02207996.pd

Meso- and macrozooplankton communities in the Weddell Sea, Antarctica

The present paper describes composition and abundance of meso- and macrozooplankton in the epipelagic zone of the Weddell Sea and gives a systematic review of encountered species regarding results of earlier expeditions. Material was sampled from 6 February to 10 March 1983 from RV Polarstern with a RMT 1+8 m (320 and 4500 μm mesh size). In agreement with topography and water mass distribution three distinct communities were defined, clearly separated by cluster analysis: The Southern Shelf Community has lowest abundances (approx. 9000 ind./1000 m3). Euphausia crystallorophias and Metridia gerlachei are predominating. Compared with the low overall abundance the number of regularly occurring species is high (55) due to many neritic forms. Herbivores and omnivores are dominating (58% and 35%). The North-eastern Shelf Community has highest abundances (about 31 000 ind./1000 m3). It is predominated by copepodites I–III of Calanus propinquus and Calanoides acutus (61%). The faunal composition is characterized by both oceanic and neritic species (64). Fine-filter feeders are prevailing (65%). The Oceanic Community has a mean abundance of approximately 23 000 ind./1000 m3, consisting of 61 species. Dominances are not as pronounced as in the shelf communities. Apart from abundant species like Calanus propinquus, Calanoides acutus, Metridia gerlachei, Oithona spp. and Oncaea spp. many typical inhabitants of the Eastwind Drift are encountered. All feeding types have about the same importance in the Oceanic Community