Quantifyingα-diversity as a continuous function of location——a case study of a temperate forest

α-diversity describes species diversity at local scales.The Simpson’s and Shannon-Wiener indices are widely used to characterizeα-diversity based on species abundances within a fixed study site(e.g.,a quadrat or plot).Although such indices provide overall diversity estimates that can be analyzed,their values are not spatially continuous nor applicable in theory to any point within the study region,and thus they cannot be treated as spatial covariates for analyses of other variables.Herein,we extended the Simpson’s and Shannon-Wiener indices to create point estimates ofα-diversity for any location based on spatially explicit species occurrences within different bandwidths(i.e.,radii,with the location of interest as the center).For an arbitrary point in the study region,species occurrences within the circle plotting the bandwidth were weighted according to their distance from the center using a tri-cube kernel function,with occurrences closer to the center having greater weight than more distant ones.These novel kernel-basedα-diversity indices were tested using a tree dataset from a 400 m×400 m study region comprising a 200 m×200 m core region surrounded by a 100-m width buffer zone.Our newly extendedα-diversity indices did not disagree qualitatively with the traditional indices,and the former were slightly lower than the latter by<2%at medium and large band widths.The present work demonstrates the feasibility of using kernel-basedα-diversity indices to estimate diversity at any location in the study region and allows them to be used as quantifiable spatial covariates or predictors for other dependent variables of interest in future ecological studies.Spatially continuousα-diversity indices are useful to compare and monitor species trends in space and time,which is valuable for conservation practitioners.

Changes in Natural Mortality of Atlantic Cod(Gadus morhua) on Eastern Georges Bank

The assessment of Eastern Georges Bank cod with the assumption of a constant natural mortality of 0.2 has over-estimated stock productivity, resulting in a severe retrospective pattern since the late 2000 s. Comparing relative exploitation rate(ratio of fishery catch at age to survey abundance indices at age) with total mortality calculated from the age distribution in surveys indicated a conflict when constant natural mortality was assumed. This inconsistency implies an increase in natural mortality since the mid-1990 s. In this paper, natural mortality estimated by Virtual Population Analysis(VPA) indicated that natural mortality for this stock has increased to 0.8 since the mid-1990 s for ages 6+. Potential factors contributing to this elevated natural mortality, including poor fish conditions and increased losses due to seal predation were discussed.

Effect of diets on the feeding behavior and physiological properties of suspension-feeding sea cucumber Cucumaria frondosa

The suspension-feeding sea cucumber Cucumaria frondosa has become commercially important in recent years.Finding proper diets is the first important step for intensive aquaculture of this sea cucumber.In this study,adult C.frondosa were exposed to one of the following diet treatments:control(no diet provided),two powdered seaweeds(Ascophyllum nodosum and Saccharina latissima),a commercially available microalgal diet(shellfish diet)and natural seston.The effects of diets on the feeding behavior and physiological properties of sea cucumbers were investigated after a 5-week rearing period.Results show that sea cucumbers fed with shellfish diet exhibited a significantly higher tentacle insertion rate(1.80±0.20 insertion/min)than these fed with seaweed powders,and there was no significant different between the two groups fed by seaweed powders.No significant difference was found on the fecal production rate among the feeding groups.The minimum oxygen consumption rate was observed in the control group(5.76±0.99μg O2/(g·h)),which is significantly lower than individuals fed with A.nodosum,shellfish diet,and natural seston;however,no significant difference was shown between those of control and S.latissimi groups.The maximum ammonium excretion rate was found in the A.nodosum group(0.03±0.01μmol/(g·h)),which is significantly higher than other groups.The minimum O/N ratio was observed in the A.nodosum group(14.57±1.04),which is significantly lower than the S.latissima,shellfish diet,and natural seston groups.Individuals fed with seaweed powders had similar physiological properties with these fed with microalgae diet and natural seston,indicating that A.nodosum and S.latissima can be explored as promising diets for intensive aquaculture of C.frondosa.