Assessing conservation status with extensive but low-resolution data: Application of frequentist and Bayesian models to endangered Athabasca River rainbow trout

Use of extensive but low-resolution abundance data is common in the assessment of species at-risk status based on quantitative decline criteria under International Union for Conservation of Nature (IUCN) and national endangered species legislation. Such data can be problematic for 3 reasons. First, statistical power to reject the null hypothesis of no change is often low because of small sample size and high sampling uncertainty leading to a high frequency of type II errors. Second, range-wide assessments composed of multiple site-specific observations do not effectively weight site-specific trends into global trends. Third, uncertainty in site-specific temporal trends and relative abundance are not propagated at the appropriate spatial scale. A common result is the propensity to underestimate the magnitude of declines and therefore fail to identify the appropriate at-risk status for a species. We used 3 statistical approaches, from simple to more complex, to estimate temporal decline rates for a designatable unit (DU) of rainbow trout in the Athabasca River watershed in western Canada. This DU is considered a native species for purposes of listing because of its genetic composition characterized as >0.95 indigenous origin in the face of continuing introgressive hybridization with introduced populations in the watershed. Analysis of abundance trends from 57 time series with a fixed-effects model identified 33 sites with negative trends, but only 2 were statistically significant. By contrast, a hierarchical linear mixed model weighted by site-specific abundance provided a DU-wide decline estimate of 16.4% per year and a 3-generation decline of 93.2%. A hierarchical Bayesian mixed model yielded a similar 3-generation decline trend of 91.3% and the posterior distribution showed that the estimate had a >99% probability of exceeding thresholds for an endangered listing. We conclude that the Bayesian approach was the most useful because it provided a probabilistic statement of threshold exceedance in support of an at-risk status recommendation.     

Nitrogen fixation (acetylene reduction) in the phyllosphere of Thalassia testudinum

N₂ fixation (C₂H₂ reduction) associated with the leaves of the sea grass Thalassia testudinum was investigated at 5 sites in South Florida (Biscayne Bay) and one site in the Bahamas (Bimini Harbor). Significant activities were correlated with the occurrence of a heterocystous blue-green alga (Calothrix sp.) on the leaves. C₂H₂ reduction was not stimulated by organic compounds, either aerobically or anaerobically in the light or dark. Therefore, other physiological types of microbes were not important in N₂ fixation. Diurnal and seasonal variations in N₂ fixation occurred, with maximal rates during the daytime and in the late spring and early summer. N₂ fixation was negligible at four stations in Biscayne Bay. At the fifth station, near Fowey Rock, about 5 kg N ha^-1 year^-1 was fixed. In the summer, the N₂ fixed per day (4–5 mg N m^-2) could provide 4 to 23% of the foliar productivity demands of T. testudinum at this site and the station in Bimini Harbor. N₂ fixation at the periphery of a sea-grass patch, near Fowey Rock, could provide 8 to 38% of the daily nitrogen requirement for leaf production, and thereby might compensate for a less effective trapping and recycling of nitrogen from dead leaves in such regions.     

Effects of different management strategies on long-term trends of Australian threatened and near-threatened mammals

Monitoring is critical to assess management effectiveness, but broadscale systematic assessments of monitoring to evaluate and improve recovery efforts are lacking. We compiled 1808 time series from 71 threatened and near-threatened terrestrial and volant mammal species and subspecies in Australia (48% of all threatened mammal taxa) to compare relative trends of populations subject to different management strategies. We adapted the Living Planet Index to develop the Threatened Species Index for Australian Mammals and track aggregate trends for all sampled threatened mammal populations and for small (<35 g), medium (35–5500 g), and large mammals (>5500 g) from 2000 to 2017. Unmanaged populations (42 taxa) declined by 63% on average; unmanaged small mammals exhibited the greatest declines (96%). Populations of 17 taxa in havens (islands and fenced areas that excluded or eliminated introduced red foxes [Vulpes vulpes] and domestic cats [Felis catus]) increased by 680%. Outside havens, populations undergoing sustained predator baiting initially declined by 75% but subsequently increased to 47% of their abundance in 2000. At sites where predators were not excluded or baited but other actions (e.g., fire management, introduced herbivore control) occurred, populations of small and medium mammals declined faster, but large mammals declined more slowly, than unmanaged populations. Only 13% of taxa had data for both unmanaged and managed populations; index comparisons for this subset showed that taxa with populations increasing inside havens declined outside havens but taxa with populations subject to predator baiting outside havens declined more slowly than populations with no management and then increased, whereas unmanaged populations continued to decline. More comprehensive and improved monitoring (particularly encompassing poorly represented management actions and taxonomic groups like bats and small mammals) is required to understand whether and where management has worked. Improved implementation of management for threats other than predation is critical to recover Australia's threatened mammals.     

The annual cycle of heterotrophic planktonic ciliates in the waters surrounding the Isles of Shoals,Gulf of Maine: an assessment of their trophic role

Macrofauna living on subtidal rocks reefs in southern California excrete ammonium, a potentially important nutrient for benthic algae. Ammonium excretion rates of eleven macroinvertebrate and five fish taxa were determined from a total of 324 in situ incubations conducted between October 1984 and August 1985 at 14 to 17 m depths off Santa Catalina Island, California. Total ammonium excretion ranged from over 100 mol h^-1 by the kelp bass Paralabrax clathratus to less than 0.1 mol h^-1 by the gastropod Conus californicus. Weight-specific ammonium excretion generally ranged from 0.5 to 4 mol g^-1 h^-1 in invertebrates and from 3 to 7 mol g^-1 h^-1 in fishes. Intraspecific excretion rates varied substantially. Coefficient of variation of excretion rates were higher than reported for laboratory studies and multiple regression indicated that 50 to 90% of the variation in ammonium excretion rates of five species studied in detail could not be explained by the combined variation in dry weight, water temperature, time of day, and incubation dates. The excretion data, along with estimates of population densities and size-frequency distributions, indicate that benthic macrofauna release a total of 25 to 30 mol NH ₄ ⁺ m^-2 h^-1 both day and night. The species that generally make the largest contributions are a gobiid fish (Lythrypnus dalli), followed by three gastropods (Astraea undosa, Tegula eiseni, and T. aureotincta) and a sea urchin (Centrostephanus coronatus). The amount of ammonium excreted by these macrofauna on rocky reefs is insignificant compared to our previously published data on the nighttime excretion of blacksmith (Chromis punctipinnis), a pomacentrid fish that feeds in the water column during the day and shelters on the reef at night. Including blacksmiths, we estimate that the amount released by rocky-reef macrofauna at night is >280 mol m^-2 h^-1, a rate that is similar to that for many other marine communities. Additional studies are required to determine if benthic algae utilize ammonium released by these macrofauna, especially at night.Contribution No. 58 of the Ocean Studies Institute; Contribution No. 123 of the Catalina Marine Science Center     

Species-specific influence of group composition on collective behaviors in ants

The success of a social group is often driven by its collective characteristics and the traits of its individuals. Thus, understanding how collective behavior is influenced by the behavioral composition of group members is an important first step to understand the ecology of collective personalities. Here, we investigated how the efficiency of several group behaviors is influenced by the aggressiveness of its members in two species of Temnothorax ants. In our manipulation of group composition, we created two experimentally reconstituted groups in a split-colony design, i.e., each colony was split into an aggressive and a docile group of equal sizes. We found strong species-specific differences in how collective behaviors were influenced by its group members. In Temnothorax longispinosus, having more aggressive individuals improved colony defense and nest relocation efficiency. In addition, source colony identity strongly influenced group behavior in T. longispinosus, highlighting that manipulations of group compositions must control for the origin of the chosen individuals. In contrast, group composition and source colony did not influence collective behaviors in Temnothorax curvispinosus. This suggests that the mechanisms regulating collective behaviors via individual differences in behavior might differ among even closely related species.     

Copper-catalyzed chlorination and condensation of acetylene and dichloroacetylene

The chlorination and condensation of acetylene at low temperatures is demonstrated using copper chlorides as chlorinated agents coated to model borosilicate surfaces. Experiments with and without both a chlorine source and borosilicate surfaces indicate the absence of gas-phase and gas-surface reactions. Chlorination and condensation occur only in the presence of the copper catalyst. C₂ through C₈ organic products were observed in the effluent; PCDD/F were only observed from extraction of the borosilicate surfaces. A global reaction model is proposed that is consistent with the observed product distributions. Similar experiments with dichloroacetylene indicate greater reactivity in the absence of the copper catalyst. Reaction is observed in the gas-phase and in the presence of borosilicate surfaces at low temperatures. The formation of hexachlorobenzene is only observed in the presence of a copper catalyst. PCDD/F were only observed from extraction of the borosilicate surfaces. A global reaction model is proposed for the formation of hexachlorobenzene from dichloroacetylene.     

The use of benthic mesocosms for the assessment of sediment contamination.

The diagnostic capability of changes in the benthic macroinvertebrate community composition to determine the cause in contaminated sediments were addressed using box core mesocosms subjected to cadmium, atrazine and nutrient enrichment. Intact cores of lake sediment were collected from Lake Erie at four occasions during 1996 and were returned to laboratory where they were maintained and manipulated. The benthic community composition of the artificially polluted mesocosms was compared with field data, collected at the same time as the intact cores, and to untreated control boxes. Community composition was related to the measured environmental variables using multi-dimensional scaling (MDS) and principle axis correlation (PCC). Community responses to different treatments were both different and consistent, suggesting that the community structure of these mesocosms could be used to identify the primary source of impact.