Foraging efficiency of juvenile bluegill, Lepomis macrochirus, among different vegetated habitats

Optimal foraging theory is devoted to understanding how organisms maximize net energy gain. However, both the theory and empirical studies lack critical components, such as effects of environmental variables across habitats. We addressed the hypothesis that energetic returns of juvenile bluegill are affected by environmental variables characteristic of the vegetated habitats. Predicted optimal diet breadths were calculated and compared to prey items eaten by juvenile bluegill to determine if bluegill were foraging to maximize energetic gain. Differences in habitat profitability among vegetated sites were determined by comparing predictions of maximized energetic return rates (cals^-1) with prey contents of bluegill stomachs. Sizes of most prey items eaten by juvenile bluegill throughout the vegetated sites were smaller than the predicted optimal diet breadths. However, inclusion of smaller prey items in the diet did not seem to affect rate of energetic gain. Energetic return rates were maximized at the 1.5 and 2mm prey size classes and declined only slightly with inclusion of smaller prey sizes. Predicted energetic return rates and average mass in bluegill stomachs were related negatively. Average mass in bluegill stomachs also was associated negatively with Elodea canadensis stem densities and percent of light transfer, suggesting that foraging efficiency of bluegill decreased as plant density and percent of light increased. Results of our research indicate that maximization of energetic return rates is dependent upon availability of prey sizes that contribute to optimal foraging. Thus, determination of those habitats that provide the highest availability of benthic invertebrate prey with the least interference by stems is critical. Enhanced foraging capabilities can promote recruitment, faster growth, better body condition and survival.     

Effects of latitude, altitude and climate on the habitat and conservation of the endangered butterfly Maculinea arion and its Myrmica ant hosts

Analyses were made of the habitats of the endangered myrmecophilous butterfly, Maculinea arion, and its host ant, Myrmica sabuleti, in five regions, spanning most of the climatic range of the butterfly in west Europe. Near their altitudinal or north latitudinal limits, both species are confined to warm south-facing slopes where the turf is grazed <3 cm tall, but at low altitudes further south, where the summer climate is 4°C warmer, the butterfly and ant inhabit ground with any aspect other than south-facing, and the butterfly is restricted to swards >20 cm tall. Intermediate types of habitat were used in regions with intermediate summer climates. The implications for conservation management are discussed. The fact that M. arion has a narrow niche and occupies very early successional stages near its range-edge makes it difficult to conserve in regions with cool climates. A successful example is described from one site in the UK. During 20 years of intensive management the sward structure was altered from being tall and dense to that predicted as optimal for M. arion at its range-edge. The species of Myrmica changed greatly during this period, with thermophilous ants, including M. sabuleti, supplanting cool-loving non-host species. A population of M. arion now inhabits this site. We predict that the conservation of M. arion will be easier and cheaper to achieve under the warm climates of central lowland Europe where different, less intensive, management is required. © Rapid Science Ltd. 1998     

Determinants of local abundance in a major radiation of Australian passerines (Aves: Meliphagoidea)

Aim  To identify the factors that contribute to variation in abundance (population density), and to investigate whether habitat breadth and diet breadth predict macroecological patterns in a suborder of passerine birds (Meliphagoidea).
Location  Australia (including Tasmania).
Methods  Mean abundance data were collated from site surveys of bird abundance (the Australian Bird Count); range size and latitudinal position data from published distribution maps; and body mass and diet breadth information from published accounts. A diversity index of habitats used (habitat breadth) was calculated from the bird census data. We used bivariate correlation and multiple regression techniques, employing two phylogenetic comparative methods: phylogenetic generalized least squares and independent contrasts.
Results  Body mass and latitude were the only strong predictors of abundance, with larger-bodied and lower-latitude species existing at lower densities. Together, however, body mass and latitude explained only 11.1% of the variation in mean abundance. Range size and habitat breadth were positively correlated, as were diet breadth and body mass. However, neither range size, nor habitat breadth and diet breadth, explained patterns in abundance either directly or indirectly.
Main conclusions  Levels of abundance (population density) in meliphagoid birds are most closely linked to body mass and latitudinal position, but not range size. As with many other macroecological analyses, we find little evidence for aspects of niche breadth having an effect on patterns of abundance. We hypothesize that evolutionary age may also have a determining effect on why species tend to be rarer (less abundant) in the tropics.     

Occurrence of an invasive coral in the southwest Atlantic and comparison with a congener suggest potential niche expansion

Tubastraea tagusensis, a coral native to the Galapagos Archipelago, has successfully established and invaded the Brazilian coast where it modifies native tropical rocky shore and coral reef communities. In order to understand the processes underlying the establishment of T. tagusensis, we tested whether Maxent, a tool for species distribution modeling, based on the native range of T. tagusensis correctly forecasted the invasion range of this species in Brazil. The Maxent algorithm was unable to predict the Brazilian coast as a suitable environment for the establishment of T. tagusensis. A comparison between these models and a principal component analysis (PCA) allowed us to examine the environmental dissimilarity between the two occupied regions (native and invaded) and to assess the species' occupied niche breadth. According to the PCA results, lower levels of chlorophyll‐a and nitrate on the Atlantic coast segregate the Brazilian and Galapagos environments, implying that T. tagusensis may have expanded its realized niche during the invasion process. We tested the possible realized niche expansion in T. tagusensis by assuming that Tubastraea spp. have similar fundamental niches, which was supported by exploring the environmental space of T. coccinea, a tropical‐cosmopolitan congener of T. tagusensis. We believe that the usage of Maxent should be treated with caution, especially when applied to biological invasion (or climate change) scenarios where the target species has a highly localized native (original) distribution, which may represent only a small portion of its fundamental niche, and therefore a violation of a SDM assumption.     

Unique biomechanical interactions between myeloma cells and bone marrow stroma cells

We observed that BMSCs (bone marrow stromal cells) from myeloma patients (myeloma BMSCs) were significantly stiffer than control BMSCs using a cytocompression device. The stiffness of myeloma BMSCs and control BMSCs was further increased upon priming by myeloma cells. Additionally, myeloma cells became stiffer when primed by myeloma BMSCs. The focal adhesion kinase activity of myeloma cells was increased when cells were on stiffer collagen gels and on myeloma BMSCs. This change in myeloma stiffness is associated with increased colony formation of myeloma cells and FAK activation when co-cultured with stiffer myeloma BMSCs or stiffer collagen. Additionally, stem cells of RPMI8226 cells became stiffer after priming by myeloma BMSCs, with concomitant increases of stem cell colony formation. These results suggest the presence of a mechanotransduction loop between myeloma cells and myeloma BMSCs to increase the stiffness of both types of cells via FAK activation. The increase of stiffness may in turn support the growth of myeloma cells and myeloma stem cells.     

Human CD133-derived bone marrow stromal cells establish ectopic hematopoietic microenvironments in immunodeficient mice

Cultured adherent bone marrow stromal cells (BMSCs) are capable of forming ectopic hematopoietic microenvironments (HMEs) in immunodeficient mice. However, the cell surface phenotype of the native bone marrow stem/progenitor cell that gives rise to BMSCs that support hematopoiesis remains poorly defined. We recently reported the derivation of human BMSC-like cells (CD133BMSCs) by magnetic cell sorting against Prominin-1 (CD133), an epitope expressed by embryonic, fetal, and adult stem cells. Here we demonstrate that CD133BMSCs are capable of forming ectopic HMEs. Cultured adherent CD133BMSCs derived from sorted CD133-positive cells lacked CD133 expression, but were uniformly positive for CD146, an epitope recently described to identify self-renewing osteoprogenitor cells that could transfer the HME. CD133BMSCs were genetically-tagged by lentivirus, expanded, and seeded into HA/TCP/fibrin constructs that were implanted subcutaneously. After 60 days, CD133BMSCs produced human osteocytes, osteoblasts, adipocytes, and reticular cells that supported murine hematopoiesis. CD133BMSCs that were not transduced with lentivirus also formed HMEs. Control constructs seeded with human dermal fibroblasts formed connective tissue, but failed to form HMEs. Our data indicate that CD133 expression identifies a native human bone marrow stem/progenitor cell that gives rise to BMSCs capable of forming the HME.     

Niche diversity in crustacean cryptic species: complementarity in spatial distribution and predation risk

Recent genetic studies indicate that species with very close phenotypic similarity (“cryptic species”) are a common feature of nature, and that such cryptic species often coexist in communities. Because traditional views of species coexistence demand that species differ in phenotype to coexist stably, the existence of sympatric cryptic species appears to challenge traditional perspectives of coexistence. We evaluated niche diversity in three recently discovered species of Hyalella amphipods that occur sympatrically in lakes and share close phenotypic similarity. We found that, in some cases, these species exhibited strong complementary spatial distributions within the littoral zone of lakes, both across a distance-from-shore gradient, and a vertical depth gradient. Additionally, we compared fish stomach contents with habitat samples and found that species differed in their vulnerability to predation from sunfish (Lepomis spp.). Complementarity among species across axes of spatial distribution and predation risk, two important niche components, suggests that species with close phenotypic similarity may differ appreciably along ecologically relevant axes. Our results, considered in the light of previous studies, suggest a community structured by predator-mediated coexistence or sequential dominance across environmental gradients in the littoral zone.     

Natural selection on ecophysiological traits of a fern species in a temperate rainforest

Unlike other species of the genus Blechnum, the fern Blechnum chilense occurs in a wide range of habitats in Chilean temperate rainforest, from shaded forest understories to abandoned clearings and large gaps. We asked if contrasting light environments can exert differential selection on ecophysiological traits of B. chilense. We measured phenotypic selection on functional traits related to carbon gain: photosynthetic capacity (A _max), dark respiration rate (R _d), water use efficiency (WUE), leaf size and leaf thickness in populations growing in gaps and understorey environments. We assessed survival until reproductive stage and fecundity (sporangia production) as fitness components. In order to determine the potential evolutionary response of traits under selection, we estimated the genetic variation of these traits from clonally propagated individuals in common garden experiments. In gaps, survival of B. chilense was positively correlated with WUE and negatively correlated with leaf size. In contrast, survival in shaded understories was positively correlated with leaf size. We found positive directional fecundity selection on WUE in gaps population. In understories, ferns of lower R _d and greater leaf size showed greater fecundity. Thus, whereas control of water loss was optimized in gaps, light capture and net carbon balance were optimized in shaded understories. We found a significant genetic component of variation in WUE, R _d and leaf size. This study shows the potential for evolutionary responses to heterogeneous light environments in functional traits of B. chilense, a unique fern species able to occupy a broad successional niche in Chilean temperate rainforest.