How complex do models need to be to predict dispersal of threatened species through matrix habitats?

Persistence of species in fragmented landscapes depends on dispersal among suitable breeding sites, and dispersal is often influenced by the "matrix" habitats that lie between breeding sites. However, measuring effects of different matrix habitats on movement and incorporating those differences into spatially explicit models to predict dispersal is costly in terms of time and financial resources. Hence a key question for conservation managers is: Do more costly, complex movement models yield more accurate dispersal predictions? We compared the abilities of a range of movement models, from simple to complex, to predict the dispersal of an endangered butterfly, the Saint Francis' satyr (Neonympha mitchellii francisci). The value of more complex models differed depending on how value was assessed. Although the most complex model, based on detailed movement behaviors, best predicted observed dispersal rates, it was only slightly better than the simplest model, which was based solely on distance between sites. Consequently, a parsimony approach using information criteria favors the simplest model we examined. However, when we applied the models to a larger landscape that included proposed habitat restoration sites, in which the composition of the matrix was different than the matrix surrounding extant breeding sites, the simplest model failed to identify a potentially important dispersal barrier, open habitat that butterflies rarely enter, which may completely isolate some of the proposed restoration sites from other breeding sites. Finally, we found that, although the gain in predicting dispersal with increasing model complexity was small, so was the increase in financial cost. Furthermore, a greater fit continued to accrue with greater financial cost, and more complex models made substantially different predictions than simple models when applied to a novel landscape in which butterflies are to be reintroduced to bolster their populations. This suggests that more complex models might be justifiable on financial grounds. Our results caution against a pure parsimony approach to deciding how complex movement models need to be to accurately predict dispersal through the matrix, especially if the models are to be applied to novel or modified landscapes.     

Flux by fin: fish-mediated carbon and nutrient flux in the northeastern Gulf of Mexico

Seagrass meadows are among the most productive ecosystems in the marine environment. It has been speculated that much of this production is exported to adjacent ecosystems via the movements of organisms. Our study utilized stable isotopes to track seagrass-derived production into offshore food webs in the northeastern Gulf of Mexico. We found that gag grouper (Myctereoperca microlepis) on reefs as far as 90 km from the seagrass beds incorporate a significant portion of seagrass-derived biomass. The muscle tissue of gag grouper, a major fisheries species, was composed on average of 18.5–25% seagrass habitat-derived biomass. The timing of this annual seagrass subsidy appears to be important in fueling gag grouper egg production. The δ³⁴S values of gag grouper gonad tissues varied seasonally and were δ³⁴S depleted during the spawning season indicating that gag utilize the seagrass-derived biomass to support reproduction. If such large scale trophic subsidies are typical of temperate seagrass systems, then loss of seagrass production or habitat would result in a direct loss of offshore fisheries productivity.     

Multiple lineages and absence of panmixia in the “circumpolar” crinoid <Emphasis Type="Italic">Promachocrinus kerguelensis</Emphasis> from the Atlantic sector of Antarctica

Despite considerable interest in physiology, evolution and life history of Antarctic marine invertebrates, only a limited number of studies have examined the genetic variability and diversity patterns of these organisms. Moreover, understanding and characterizing patterns of Antarctic biodiversity has taken on a degree of urgency because of potential impacts of global warming. To expand an understanding of the evolutionary history of Antarctic marine invertebrates, the genetic diversity of the crinoid Promachocrinuskerguelensis Carpenter, 1888 was investigated, which is documented to have a circumpolar distribution extending to subantarctic islands. Specimens of P. kerguelensis were collected from the western side of the Antarctic Peninsula, and the subantarctic islands South Georgia, South Sandwich and Bouvetøya Island from 2001 to 2004. P. kerguelensis was previously subject to morphological review that confirmed the taxonomic recognition of only one species. The wide distribution and reported high dispersal capability for P. kerguelensis predicts one large panmictic population. In contrast, nucleotide sequence data from mitochondrial cytochrome oxidase subunit I and cytochrome b genes, collected herein, reveal distinct genetic structure and cryptic speciation within P.kerguelensis. In the Antarctic Atlantic sector alone, there were at least five “species-level” clades. Some of these clades are geographically limited, and most exist in sympatry. The largest and most widespread of these clades was examined to help elucidate connectivity along the subantarctic islands of the Scotia Arc and the Antarctic Peninsula. Within this clade, most genetic diversity was contained within populations, but significant differences were present between regions (Antarctic Peninsula, South Sandwich Is., South Georgia, Bouvetøya Is.), suggesting a corresponding lack of gene flow. Given that P. “kerguelensis” is a well-studied taxon, the finding of considerable genetic diversity within the Atlantic sector alone suggests that the recognized diversity of Antarctica’s benthic marine life may be underestimated, and will rise dramatically with phylogeographic analyses of putative widespread species.     

Competition, resources, and vegetation during 10 years in native grassland

A 10-year experiment tested for variation in competition intensity over time in a natural grassland at the northern edge of the Great Plains. Growing-season precipitation varied fivefold during the study. All ecosystem-level variables varied significantly among years, and most covaried in expected ways. The covers of all common grasses possessing the C3 photosynthetic pathway varied significantly among years; in contrast, all common species with traits associated with drought tolerance (a C4 grass, a lichen, a spikemoss, and a subshrub) did not vary. Annual transplant experiments measured the competitive effects of neighbors on the growth of individuals of the native grass Bouteloua gracilis. A significant interaction between year and competition showed that competition intensity varied among years. The size of this effect, however, was small (eta2 = 0.074) relative to the size of the direct effect of competition (eta2 = 0.20) or the year in which the experiment was conducted (eta2 = 0.51). Further, competition intensity was not significantly related to any variable describing standing crop or resources, or species richness. Species richness was highest in years with high precipitation, standing crop, and individual growth, due to the recruitment of rare species that were absent from dry years. In summary, variation in competition intensity was statistically significant but had small effects relative to the direct effects of climate.     

Safety in numbers and the spatial scaling of density-dependent mortality in a coral reef fish

In coral reef fishes, density-dependent population regulation is commonly mediated via predation on juveniles that have recently settled from the plankton. All else being equal, strong density-dependent mortality should select against the formation of high-density aggregations, yet the juveniles of many reef fishes aggregate. In light of this apparent contradiction, we hypothesized that the form and intensity of density dependence vary with the spatial scale of measurement. Individual groups might enjoy safety in numbers, but predators could still produce density-dependent mortality at larger spatial scales. We investigated this possibility using recently settled juvenile bluehead wrasse, Thalassoma bifasciatum, a small, aggregating reef fish. An initial caging experiment demonstrated that juvenile bluehead wrasse settlers suffer high predation, and spatial settlement patterns indicated that bluehead wrasse juveniles preferentially settle in groups, although they are also found singly. We then monitored the mortality of recently settled juveniles at two spatial scales: microsites, occupied by individual fish or groups of fish and separated by centimeters, and sites, consisting of approximately 2400-m2 areas of reef and separated by kilometers. At the microsite scale, we measured group size and effective population density independently and found that per capita mortality decreased with group size but was not related to density. At the larger spatial scale, however, per capita mortality increased with settler density. This shift in the form of density dependence with spatial scale could reconcile the existence of small-scale aggregative behavior typical of many reef fishes with the population-scale density dependence that is essential to population stability and persistence.     

Direct and indirect methods for chromium identification in industrial wastes

The examinations of selected wastes and stream sediments from the vicinity of a chemical plant by sequential extraction procedures and direct methods, SEM/EDX and XRD, were carried out in order to identify the different forms of chromium, particularly as they are released to potential mobility. The results show that the top and bottom waste samples contain 37,756 and 53,650 μg g¹ Cr, respectively, but about 7% and 2% of the total chromium type Cr(VI). The chemical extraction results show that the mobility of Cr in the upper part of the waste pile is significantly higher than in the bottom section; the exchangeable form of Cr accounts for 25% and < 1%, respectively, the last one irrespective of redox conditions. About 50% of Cr is associated with the reducible fraction of the top waste, and similar with the residual fraction in the bottom waste. Oxidation of the bottom waste shift some portion of Cr from residual to the moderately reducible fraction. The major Cr-forms in the river sediments are compounded with Fe-oxides. The < 2 μm size fraction of the selected sediment sample, particular enriched in chromium contained up to 73,000 μg g¹ Cr with about 95% of this in the moderately reducible fraction, predominantly bound with oxyhydroxides. SEM/EDX and XRD analysis of wastes and river sediment indicate that the main insoluble Cr-phase is ferroan — (Mg, Fe) (Cr, Al)²O⁴ which would be dissolved mainly in the residual fraction.     

Spawning and development in <Emphasis Type="Italic">Osedax</Emphasis> boneworms (Siboglinidae,Annelida)

We report observations on spawning and early development in bone-eating worms of the genus Osedax. Individual females of Osedax rubiplumus were observed at 1820 m depth freely spawning hundreds of oocytes, and females of an undescribed species, Osedax “orange collar”, were observed spawning in laboratory aquaria. Cytological and molecular analysis of the spawned oocytes of two Osedax species revealed no evidence for the bacterial endosymbionts that the female worms require for their nutrition, suggesting that the bacteria must be acquired later from the environment, as they are in other siboglinids. Individual O. “orange collar” females released an average of 335 (±130) eggs per day, but the number of oocytes spawned per day varied greatly, suggesting that not all the females spawned daily. Fertilization rates of the spawned oocytes varied from 0 to 100%, though most females showed nearly 100% fertilization rates. Oocytes spawned in the laboratory at 4–6°C were negatively buoyant. If fertilized, these oocytes extruded polar bodies and then after at least four hours cleaved unequally. Subsequent cleavages occurred in a spiral pattern at roughly 2-h intervals, resulting in free-swimming trochophore larvae after 24 h. These lecithotrophic trochophores swam for 9–16 days before settling with several hooked chaetae, similar to those of dwarf Osedax males. The larval life span of the Osedax species studied in the laboratory appears to be shorter than in closely related Vestimentifera. Osedax rubiplumus, on the other hand, has much larger oocytes and so may have greater dispersal potential than these other Osedax species. The high fecundity and apparently continuous reproduction of Osedax boneworms permits the opportunistic exploitation of sunken vertebrate bones. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Aggressive mating as a tragedy of the commons in the water strider Aquarius remigis

The tragedy of the commons usually refers to the overexploitation of resources such as food or water. Here, we show in a laboratory study that competition among males for females can also result in a tragedy of the commons’ situation. Male water striders (Aquarius remigis) vary widely in their aggressiveness toward pursuing females. The most aggressive males prevent females from feeding and cause them to leave the water surface, where they are unavailable to all males. Groups of nonaggressive males are collectively three times more fit than groups of hyperaggressive males, but hyperaggressive males are more successful than nonaggressive males within mixed groups. This is the classic tragedy of the commons’ situation, and it is likely to occur in many species that exhibit sexual conflict. We have also shown that individual differences in male aggression are stable across time and are not influenced by food or light regime, although all individuals become nonaggressive in the presence of fish predators.     

Organisational resilience following the Darfield earthquake of 2010

This paper presents the preliminary findings of a study on the resilience and recovery of organisations following the Darfield earthquake in New Zealand on 4 September 2010. Sampling included organisations proximal and distal to the fault trace, organisations located within central business districts, and organisations from seven diverse industry sectors. The research captured information on the challenges to, the impacts on, and the reflections of the organisations in the first months of recovery. Organisations in central business districts and in the hospitality sector were most likely to close, while organisations that had perishable stock and livestock were more heavily reliant on critical services. Staff well‐being, cash flow, and customer loss were major concerns for organisations across all sectors. For all organisations, the most helpful factors in mitigating the effects of the earthquake were their relationship with staff members, the design and type of buildings, and critical service continuity or swift reinstatement of services.     

The Effects of Liming On Soil Chemistry at Loch Fleet,Scotland

An experiment to investigate how the water quality of acid lakes can be improved by liming the surrounding catchment was begun at Loch Fleet, Scotland in 1984. the effects on the soils of three sectors of the catchment where limestone was added in 1986 are reported here, following analysis of soils sampled in 1987, 1988 and 1991. the effect of the lime on soil chemistry was still evident in 1991, with about 15% of free lime remaining in the hydrochemical reaction zone of sectors IV and VI and nearly 50% in sector VII. However, this free lime appeared to be dissolving too slowly to maintain large amounts of exchangeable calcium in the soils, indicating that the treatment is starting to become less effective. the fall in the mean exchangeable calcium in the reaction zone between 1988 and 1991 was mirrored by a drop in mean soil pH over the 5 years post-liming from 6.1 to 5.6 on sector IV and from 5.9 to 5.4 on sector VI, whereas mean pH remained constant at about 6.0 in the limed areas of sector VII. Using soil data to predict longevity suggests that the exchangeable calcium remaining on the catchment at the end of 1991 will maintain target water quality in the loch until sometime during 1994. the soil pH is likely to fall to between 5.2 and 5.3 by this time. If the region of hydrochemical reaction is assumed to extend to a depth of 20 cm rather than 5 cm, target water quality is predicted to be maintained until the end of 1995. When the free lime remaining on the catchment is included as a source of acid neutralising capacity, calculations show that treatment may remain effective until around the year 2000.