The importance of space, time, and stochasticity to the demography and management of Alliaria petiolata

As population modeling is increasingly called upon to guide policy and management, it is important that we understand not only the central tendencies of our study systems, but the consequences of their variation in space and time as well. The invasive plant Alliaria petiolata (garlic mustard) is actively managed in the United States and is the focus of a developing biological control program. Two weevils (Coleoptera: Curculionidae: Ceutorhynchus) that reduce fecundity (C. alliariae) and rosette survival plus fecundity (C. scrobicollis) are under consideration for release pending host specificity testing. We used a demographic modeling approach to (1) quantify variability in A. petiolata growth and vital rates and (2) assess the potential for single- or multiple-agent biocontrol to suppress growth of 12 A. petiolata populations in Illinois and Michigan studied over three plant generations. We used perturbation analyses and simulation models with stochastic environments to estimate stochastic growth rates (lambda(S)) and predict the probability of successful management using either a single biocontrol agent or two agent species together. Not all populations exhibited invasive dynamics. Estimates of lambda(S) ranged from 0.78 to 2.21 across sites, while annual, deterministic growth (lambda) varied up to sevenfold within individual sites. Given our knowledge of the biocontrol agents, this analysis suggests that C. scrobicollis alone may control A. petiolata at up to 63% of our study sites where lambda >1, with the combination of both agents predicted to succeed at 88% of sites. Across sites and years, the elasticity rankings were dependent on lambda. Reductions of rosette survival, fecundity, or germination of new seeds are predicted to cause the greatest reduction of lambda in growing populations. In declining populations, transitions affecting seed bank survival have the greatest effect on lambda. This contrasts with past analyses that varied parameters individually in an otherwise constant matrix, which may yield unrealistic predictions by decoupling natural parameter covariances. Overall, comparisons of stochastic and deterministic growth rates illustrate how analyses of individual populations or years could misguide management or fail to characterize complex traits such as invasiveness that emerge as attributes of populations rather than species.     

Evaluating the performance of methods for estimating the abundance of rapidly declining coastal shark populations

Accurately surveying shark populations is critical to monitoring precipitous ongoing declines in shark abundance and interpreting the effects that these reductions are having on ecosystems. To evaluate the effectiveness of existing survey tools, we used field trials and computer simulations to critically examine the operation of four common methods for counting coastal sharks: stationary point counts, belt transects, video surveys, and mark and recapture abundance estimators. Empirical and theoretical results suggest that (1) survey method selection has a strong impact on the estimates of shark density that are produced, (2) standardizations by survey duration are needed to properly interpret and compare survey outputs, (3) increasing survey size does not necessarily increase survey precision, and (4) methods that yield the highest density estimates are not always the most accurate. These findings challenge some of the assumptions traditionally associated with surveying mobile marine animals. Of the methods we trialed, 8 x 50 m belt transects and a 20 m radius point count produced the most accurate estimates of shark density. These findings can help to improve the ways we monitor, manage, and understand the ecology of globally imperiled coastal shark populations.     

Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.     

Sighting characteristics and photo-identification of Cuvier’s beaked whales (<Emphasis Type="Italic">Ziphius cavirostris</Emphasis>) near San Clemente Island,California: a key area for beaked whales and the military?

The relationship between beaked whales and certain anthropogenic sounds remains poorly understood and of great interest. Although Cuvier’s beaked whales (Ziphius cavirostris) are widely distributed, little is known of their behavior and population structure throughout much of their range. We conducted a series of five combined visual-acoustic marine mammal surveys from 2006 to 2008 in the southern San Nicolas Basin, a site of frequent naval activity off the southern California coast, west of San Clemente Island. The study area was defined by a 1,800 km² array of 88 bottom-mounted hydrophones at depths up to 1,850 m. The array was used to vector visual observers toward vocalizing marine mammal species. Thirty-seven groups of Cuvier’s beaked whales were encountered during the study period. The overall encounter rate was one group for every 21.0 h of survey effort, and was as high as one group per 10.2 h of effort during the October 2007 survey. Whales were encountered in the deepest portion of the study area, at a mean bottom depth of 1,580 m (SD 138). The average group size was 3.8 individuals (SD 2.4), which was higher than has been reported from other studies of this species. Twenty-four groups were observed over multiple surfacings (median = 4 surfacings, range 2–15). The mean encounter duration of extended sightings was 104 min (SD 98, range 12–466 min) and the mean distance moved over the course of sightings was 1.66 km (SD 1.56, range 0.08–6.65 km). Temporal surfacing patterns during extended encounters were similar to dive behavior described from Cuvier’s beaked whales carrying time-depth recording tags. Seventy-eight photographic identifications were made of 58 unique individuals, for an overall resighting rate of 0.26. Whales were sighted on up to 4 days, with duration from first to last sighting spanning 2–79 days. For those whales sighted on subsequent days, the mean distance between subsequent sightings was 8.6 km (SD 7.9). Individuals resighted over 2–3 days were usually in association with previous group members. Approximately one-third of groups contained more than one adult male, and many of the repeated associations involved adult males. These observations suggest the basin west of San Clemente Island may be an important region for Cuvier’s beaked whales, and also one which affords an unusual opportunity to collect detailed data on this species. Given its status as an active military range, it can also provide the ability to monitor the behavior of individuals in the presence of naval sonar, a critical step in the management of this and other beaked whale populations worldwide.     

The influence of anthropogenic and natural geochemical factors on urban soil quality variability: a comparison between Glasgow, UK and Aveiro, Portugal

As part of a harmonised assessment of urban soils (), we investigated the variability of metal content in soils from Aveiro (Portugal) and Glasgow (UK). Samples were collected from parks and other public open spaces in each city. Metal content (Al, Ca, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and basic soil parameters (texture, CEC, pH, organic matter) were determined and data investigated using principal component analysis (PCA). The two cities differ in absolute levels of metal content reflecting industrial and historical development. Factors identified by PCA included anthropogenic (Cu, Pb, Zn), soil properties and geology, which explain variability when data were assessed based on metal content, soil properties and land use. This study highlights the contribution from geological background even in strongly urbanised environments.     

Patch use and vigilance by sympatric lemmings in predator and competitor-driven landscapes of fear

Prey living in risky environments can adopt a variety of behavioral tactics to reduce predation risk. In systems where predators regulate prey abundance, it is reasonable to assume that differential patterns of habitat use by prey species represent adaptive responses to spatial variation in predation. However, patterns of habitat use also reflect interspecific competition over habitat. Collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings represent such a system and possess distinct upland tundra versus mesic meadow habitat preferences consistent with interspecific competition. Yet, we do not know whether this habitat preference might also reflect differences in predation risk or whether the two species differ in their behavioral tactics used to avoid predation. We performed experiments where we manipulated putative predation risk perceived by lemmings by increasing protective cover in upland and meadow habitats while we recorded lemming activity and behavior. Both lemming species preferentially used cover more than open patches, but Dicrostonyx was more vigilant than Lemmus. Both species also constrained their activity to protective patches in upland and meadow habitats, but during different periods of the day. Use of cover and vigilance were independent of habitat, suggesting that both species live in a fearsome but flattened landscape of fear at Walker Bay (Nunavut, Canada), and that their habitat preference is a consequence of competition rather than predation risk. Future studies aiming to map the contours of fear in multi-prey–predator systems should consider how predation and competition interact to modify prey species’ habitat preference, patch use, and vigilance.     

Using expert knowledge to support Endangered Species Act decision-making for data-deficient species

Many questions relevant to conservation decision-making are characterized by extreme uncertainty due to lack of empirical data and complexity of the underlying ecologic processes, leading to a rapid increase in the use of structured protocols to elicit expert knowledge. Published ecologic applications often employ a modified Delphi method, where experts provide judgments anonymously and mathematical aggregation techniques are used to combine judgments. The Sheffield elicitation framework (SHELF) differs in its behavioral approach to synthesizing individual judgments into a fully specified probability distribution for an unknown quantity. We used the SHELF protocol remotely to assess extinction risk of three subterranean aquatic species that are being considered for listing under the U.S. Endangered Species Act. We provided experts an empirical threat assessment for each known locality over a video conference and recorded judgments on the probability of population persistence over four generations with online submission forms and R-shiny apps available through the SHELF package. Despite large uncertainty for all populations, there were key differences between species’ risk of extirpation based on spatial variation in dominant threats, local land use and management practices, and species’ microhabitat. The resulting probability distributions provided decision makers with a full picture of uncertainty that was consistent with the probabilistic nature of risk assessments. Discussion among experts during SHELF's behavioral aggregation stage clearly documented dominant threats (e.g., development, timber harvest, animal agriculture, and cave visitation) and their interactions with local cave geology and species’ habitat. Our virtual implementation of the SHELF protocol demonstrated the flexibility of the approach for conservation applications operating on budgets and time lines that can limit in-person meetings of geographically dispersed experts.     

三峡水库春季营养盐和浮游植物空间分布及其影响机制

为研究三峡水库春季水体营养盐与浮游植物的空间分布状况,于2013年3月对三峡水库22条支流及干流的6个断面进行采样监测. 结果表明:来水、回水、河口和干流4类断面ρ(TN)平均值分别为1.69、1.84、2.01、1.51 mg/L;ρ(TP)平均值分别为0.115、0.191、0.179和0.181 mg/L;不同类型断面间ρ(TN)、ρ(TP)差异不显著;水体中N、P的主要形态分别为NO₃--N和PO₄3--P;N/P〔n(N)/n(P)〕从来水(110.8)至干流(18.9)逐渐降低. 三峡水库总体上为中营养状态,回水和河口区富营养化程度较高,富营养断面比例分别为45.4%和36.4%. 研究期间共检出浮游植物8门98属,其中以绿藻门、硅藻门和蓝藻门为主,分别检出42、26和17属;从组成上看,来水和干流断面以硅藻-绿藻为主,回水、河口断面以绿藻-硅藻为主. 浮游植物丰度由高到低依次为回水、河口、来水和干流断面. 调查期间,22条支流中有15条支流在不同位置发生水华,但主要集中在回水区;拟多甲藻水华为主要类型且集中在库区的下游支流,而库区中上游支流则以隐藻、衣藻、小球藻、小环藻等水华为主. 环境因子排序分析表明,在水华集中的回水-河口区域,影响浮游植物丰度分布的主要环境因子数明显少于其他区域,温度和ρ(DO)为该区域浮游植物丰度分布的主要影响因子,而ρ(TN)、ρ(TP)的影响不明显.      

The ghost of predation future: threat-sensitive and temporal assessment of risk by embryonic woodfrogs

Amphibians are able to learn to recognize their future predators during their embryonic development (the ghost of predation future). Here, we investigate whether amphibian embryos can also acquire additional information about their future predators, such as the level of threat associated with them and the time of day at which they would be the most dangerous. We exposed woodfrog embryos (Rana sylvatica) to different concentrations of injured tadpole cues paired with the odor of a tiger salamander (Ambystoma tigrinum) between 1500 and 1700 hours for five consecutive days and raised them for 9 days after hatching. First, we showed that embryos exposed to predator odor paired with increasing concentrations of injured cues during their embryonic development subsequently display stronger antipredator responses to the salamander as tadpoles, thereby demonstrating threat-sensitive learning by embryonic amphibians. Second, we showed that the learned responses of tadpoles were stronger when the tadpoles were exposed to salamander odor between 1500 and 1700 hours, the time at which the embryos were exposed to the salamander, than during earlier (1100–1300 hours) or later (1900–2100 hours) periods. Our results highlight the amazing sophistication of learned predator recognition by prey and emphasize the importance of temporal considerations in experiments examining risk assessment by prey.     

SEMIPERMEABLE MEMBRANE DEVICES USED TO ESTIMATE BIOCONCENTRATION OF POLYCHLORINATED BIPHENYLS1

ABSTRACT: Aquatic organisms passively accumulate hydrophobic organic compounds, such as polychlorinated biphenyls, even when ambient water concentrations of the contaminant are below analytical detection limits. However, contaminant concentrations in tissue samples are subject to an inherently high level of variability due to differences in species, life stage, and gender bioconcentration potentials. Semipermeable membrane devices (SPMDs) were used to sample Aroclor 1254, a mixture of readily bioconcentrated polychlorinated biphenyls (PCBs), in a contaminated wetland near Flat Top, WV. The devices consisted of triolein, a lipid found in fish, enclosed in a polyethylene membrane. SPMDs were deployed in the water column and in direct contact with wetland sediments along a previously identified concentration gradient of PCBs. The devices were retrieved after a 25-day exposure period. Analytes were recovered by dialyzing the devices in nanograde hexane. Hexane dialysates were condensed and analyzed by gas chromatography. All deployed devices sequestered quantifiable amounts of Aroclor 1254. Water-column SPMDs accumulated PCBs far in excess of ambient water concentrations. The devices contacting sediments accumulated PCBs at all sites, though accumulated concentrations did not exceed concentrations in sediment. Patterns of PCB concentration in the devices corresponded to the identified gradient at the site. Results from the water-column SPMDs were used to estimate the concentration of the dissolved, bioavailable fraction of PCBs present in the water column. These concentrations ranged from 0.01 to 0.09 μg/L of bioavailable Aroclor 1254.