Temporal Variation In Abundance Research Articles

Spatial and temporal variation in abundance, group size and behaviour of bottlenose dolphins in the Florida coastal Everglades

Bottlenose dolphins (Tursiops truncatus) are abundant in many coastal ecosystems, including the coastal Everglades. Understanding spatial and temporal variation in their abundance and group sizes is important for estimating their potential ecological importance and predicting how environmental changes (e.g. ecosystem restoration) might impact their populations. From August 2010 to June 2012, we completed a total of 67 belt transects covering a total of 2650 linear km and an area of 1232 km2. Dolphin densities varied spatially and temporally. The highest densities of dolphins were found in coastal oceans and inland bays and were lowest in rivers. Use of rivers, however, increased during the dry season while densities in other habitats remained similar across seasons. Dolphins appeared to prefer portions of bays close to mangrove-covered islands over open waters. A resighting rate of 63.6% of individuals across the 2-year study suggests that at least a portion of the population is probably resident within study regions over long time periods. The largest groups (mean 6.28, range 1–31) were found in open waters and bays despite apparently low predation pressure. Indeed, shark bite scars – likely the result of unsuccessful predation attempts – were conclusively observed on only 1% of individuals. Although further studies are warranted, the high densities of dolphins suggest that they are an important upper trophic level predator in the coastal Everglades, but their ecological importance probably varies in space and time.

Nematode communities in the Sai Gon River harbors in relation to tributyltin concentrations

The impact of toxic tributyltin (TBT) compounds was investigated on free-living nematode communities in the Sai Gon River. Samples were collected from 11 harbor stations downstream of the Sai Gon river plus one upstream station during the dry and rainy seasons. The results showed that all butyltin compound (mono-, di-, and tri) concentrations were relatively low compared to historical data from the same or adjacent estuaries, supporting the effectiveness of the 2009 ban on these products as antifouling. Nematode communities were typical for oligohaline regions showing a high spatial and temporal variability in abundance and diversity. Nematode community composition clearly differed between the two seasons, with the nematode communities being less variable in the rainy season compared to the dry season, while nematode communities differed significantly between stations. TBT values were still significantly negative correlated with nematode densities and selective deposit feeders during the dry season, partly confirming earlier experimental results on the response of nematodes to TBT. The historical presence of TBT contamination can possibly have caused a long-term impact on nematode communities in the Sai Gon river sediment, reflected in depressed densities during the dry season.

Temporal variations of large wood abundance and mobility in the Blanco River affected by the Chaitén volcanic eruption, southern Chile

The aim of this study is to analyze the temporal variation in abundance and transport of in-channel wood along a river affected by a volcanic eruption, considering the mobility and retention rates in detail. The 2008 eruption of Chaitén Volcano (Southern Chile) severely affected the Blanco River basin, causing changes in channel morphology and large wood (LW) dynamics along the fluvial corridor of the river, a fourth-order stream on the southern slope of the volcano. Temporal dynamics of LW were investigated, from January 2015 until March 2016, in three 80m-long study reaches of the active channel in the lower course of the river. Every wood element (≥1m in length and ≥0.1m in diameter) within the active channel of each reach was georeferenced, measured, tagged, and characterized. Wood mobility rate, defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged LW in the same reach; and retention rate, defined as the number of tagged LW pieces found within each study reach to total tagged wood pieces in the same reach, were calculated considering two periods, one in summer and one in autumn-winter. A regional flood frequency analysis estimated flood magnitude, defining a recurrence interval of ~1year for summer floods, and 10–25years for autumn-winter floods. Results highlighted how, eight years after the eruption, the types of LW are still influenced by the impacts of pyroclastic density currents on riparian vegetation. The characteristics and abundance of monitored LW are typical of a river system with frequent wood transport. The mobility rate ranges between 42 and 94% during the summer and autumn-winter period, respectively; while the wood volume decreases during the summer and increases in autumn-winter. Large wood mobility was also found to vary according to the predominant morphological settings, with lower values in narrower channels compared to wider wetted areas. In this context the greatest abundance of LW was detected after the higher floods, corresponding to an input of LW up to 285.35m3·ha−1. Along the Blanco River ordinary floods deliver LW mainly through fluvial transport, and bank erosion during higher floods appears as an additional and important wood recruitment process. The bank erosion processes, with up to 5200m2 of eroded area, confirmed the widening tendency occurring in river systems following volcanic disturbances. As there are dead riparian trees along the easily erodible banks, it is reasonable to suppose that the Blanco River will continue to widen for a long period, recruiting and transporting downstream huge volumes of LW. In this context these analyses appear of fundamental importance to better manage the river system, also for decreasing hazards to the downstream village of Chaitén.

Compounded perturbations in coastal areas: contrasting responses to nutrient enrichment and the regime of storm‐related disturbance depend on life‐history traits

Summary Natural systems are exposed to compounded perturbations, whose changes in temporal variance can be as important as those in mean intensity for shaping the structure of assemblages. Specifically, climate‐related physical disturbances and nutrient inputs due to natural and/or anthropogenic activities occur concomitantly, but experimental tests of the simultaneous effects of changes in the regime of more than one perturbation are generally lacking. Filling this gap is the key to understand ecological responses of natural assemblages to climate‐related change in the intensity and temporal patterning of physical disturbance combined with other global stressors. Responses to factorial manipulations of nutrient enrichment, mean intensity and temporal variability in storm‐like mechanical disturbance were examined, using benthic assemblages of tide‐pools as model system. Response variables were mean abundance values and temporal variances of taxa with different life‐traits. Consistent negative effects of disturbance intensity were observed for the mean cover of long‐living taxa (algal canopies and the polychaete Sabellaria alveolata), whose temporal fluctuations were also reduced by more severe mechanical stress. More resilient taxa (ephemeral algae, mostly green of the genus Ulva) increased under enriched conditions, particularly when low‐intensity events were irregularly applied over time. Opposite effects of disturbance intensity depending on nutrient availability occurred on filamentous algae (e.g. red of the genus Ceramium). This was probably due to the fact that, although nutrient enrichment stimulated the abundance of both algal groups, when this condition was combined with relatively mild physical disturbance the competitively superior ephemeral green algae tended to become dominant over filamentous red algae. The same did not occur under high intensity of disturbance since it likely damaged large, foliose fronds of Ulva‐like forms more than small, filamentous fronds of Ceramium‐like forms. Grazers were positively affected by nutrients, likely responding indirectly to more food available. A direct relationship between the mean abundance of most organisms and their temporal fluctuations was documented. However, all organisms persisted throughout the study, even under experimental conditions associated to the largest temporal variation in their abundance, likely due to their ability to resist to/quickly recover from, the applied perturbations. Therefore, in systems with great recovery abilities of dominant organisms (e.g. rocky intertidal, grasslands), effects of traits of the regime of disturbance and nutrient enrichment may modulate the fluctuations of populations not through the elimination and substitution of species, but through changes in relative abundances of the same species. This contrasts with the theory that temporal variation in abundance would be directly related to the risk of local extinction. Present findings enable more accurate predictions of the consequences of climatic and non‐climatic scenarios on the biodiversity of marine and terrestrial systems sharing analogous functional traits of organisms. Future more intense physical disturbances are expected to exert negative effects on slow‐growing/recovering species (e.g. habitat‐formers) irrespectively of the temporal patterning of the same disturbances and nutrient inputs. On the contrary, more resistant species (e.g. encrusting algae on rocky shores or below‐ground vegetation in grasslands) are expected to benefit from intense physical disturbance. Species whose abundance is more directly related to the availability of nutrients (e.g. filamentous and ephemeral algae or herbs) are expected to generally increase under enriched conditions, but their ability to eventually become dominant would depend on their ability to grow fast and attain cover large enough to overwhelm any possible control of concomitant disturbance intensity on their abundance. If, such as in the present examined system, virtually all organisms can persist, over the temporal scale of the experiment, under any combination of physical disturbance and nutrient availability, the resulting overall diversity is not predicted to change drastically. Nevertheless, low‐intensity events evenly distributed and high‐intensity events irregularly distributed appear as the conditions supporting the highest richness of taxa, independently of the availability of nutrients. A lay summary is available for this article.

An overview of Cuban seagrasses

Here, we present an overview of the current knowledge of Cuban seagrasses, including distribution, status, threats, and efforts for their conservation. It has been estimated that seagrasses cover about 50% of the Cuban shelf, with six species reported and Thalassia testudinum K. D. Koenig being the most dominant. Seagrasses have been studied primarily in three areas in Cuba (northwest, north-central, and southwest). Thalassia testudinum and other seagrasses exhibit spatial and temporal variations in abundance, and updating of their status and distribution is needed. The main threat to Cuban seagrass ecosystems is low seawater transparency due to causes such as eutrophication and erosion. High salinities limit their distribution in the Sabana-Camaguey Archipelago, partly the result of freshwater dams and roads. Seagrass meadows play important ecological roles and provide many ecosystem services in Cuba, with efforts underway to preserve this ecosystem. Research and management projects are directed toward integrated coastal zone management, including a ban on trawl fisheries and the extension of marine protected areas to contain more seagrass meadows. In addition to updating species distributions, it is urgent that managers and researchers in Cuba examine the resilience of this ecosystem in the face of climate change.

Biodiversity of suprabenthic peracarid assemblages from the Blanes Canyon region (NW Mediterranean Sea) in relation to natural disturbance and trawling pressure

Blanes Canyon and its adjacent margin are important fishery areas (mainly by bottom trawling) located in a highly energetic oceanographic setting in the NW Mediterranean Sea. Here we assess the spatial and temporal variability in abundance, diversity and community structure of the suprabenthic peracarid assemblages in this region and examine this variability in relation to the natural and anthropogenic (trawling fisheries) disturbance regimes. The sampling was conducted between March 2003 and May 2004 in three main fishing grounds, the canyon head (average depth: 490m), the canyon wall (average depth: 550m) and the eastern adjacent slope (average depth: 820m), as well as in two non-exploited areas in the western (at 900m depth) and eastern (at 1500m depth) slope near the canyon mouth. A total of 138 species were identified, with amphipods being the most speciose and abundant group, followed by mysids in terms of abundance. Our results show high spatial and temporal variability in suprabenthic assemblages. Densities were higher in the canyon head and western slope, which appear to be the preferential routes for water masses and particle fluxes in months of flood events, and other energetic processes. In the canyon head, where periodic erosion processes are more active, low diversity, high dominance and higher turnover (β-diversity) were observed, apparently coupled with significant temporal fluctuations in the densities of the highly motile component of suprabenthos (mysids, predatory and scavenging amphipods). In the sedimentary more stable eastern slope, high diversity values were observed, accompanied by a higher relative contribution of the less motile groups (i.e. amphipods, most isopods, cumaceans). These groups have a closer interaction with the sediment where they exploit different food sources and are more susceptible to physical disturbance. Temporal variability in their diversity may be related to changes in food quality rather than quantity. In the canyon wall, temporal fluctuations in diversity indices were only revealed in relation to the overall higher and more continued fishing pressure observed in the canyon wall fishing ground (Cara Norte/Sot site). Here, species richness and abundance declined with increasing fishing pressure but the lowest trophic and taxonomic diversities were observed under intermediate levels of disturbance. These findings underline (i) the differences between relatively low and highly motile taxa in terms of response to disturbance events; (ii) the differences between assemblages subjected to different levels of natural disturbance and trawling pressure, which modify the common bathymetric patterns of abundance and diversity often described from continental margins.

Temporal variations of the abundance and optical properties of water soluble Humic-Like Substances (HULIS) in PM2.5 at Guangzhou, China

Humic-Like Substances (HULIS) are important macromolecular compounds that are present in PM2.5 and play significant roles in the atmospheric environment. In this study, 48 PM2.5 samples were collected from February 2010 to January 2011 at an urban site in Guangzhou, southern China. The water soluble HULIS fractions in PM2.5 were analyzed to explore the temporal variation of abundance and optical properties and to identify their possible sources. The HULIS concentrations were in the range of 0.4 to 8.2μgCm−3, with a mean of 2.4μgCm−3. HULIS are important components in organic aerosols, accounting for 17±5% of the organic carbon (OC), and 49±6 and 68±5% of water soluble organic carbon (WSOC) as determined with a total organic carbon (TOC) analyzer and UV absorbance at 250nm, respectively. The special UV absorbance (SUVA) at 254nm and 280nm and the E250/E365 ratio of HULIS were 3.2±0.5L (mmgC)−1, 2.2±0.4L (mmgC)−1, and 5.9±0.9, respectively. The HULIS fractions had higher concentrations, slightly higher SUVA values, and lower E250/E365 ratios from November to January, indicating the important contribution of aromatic compounds to HULIS in the dry season. The concentrations of HULIS were positively correlated with water soluble K+, secondary organic carbon (SOC), and secondary inorganic ions (NH4+, NO3−, and SO42−). These results suggest that biomass burning and secondary photochemical formation are both sources of HULIS in our study area. In addition, the SUVA280 of HULIS was strongly correlated with K+ and SOC, suggesting that HULIS properties were also influenced by their primary source of biomass burning and secondary atmospheric formation.

Oithona similislikes it cool: evidence from two long-term time series

We compare the long-term and seasonal patterns of abundance and phenology of the cyclopoid copepod Oithona similis at the L4 site (1988–2013) in the North Atlantic and at the LTER-MC site (1984–2013) in the Mediterranean Sea to investigate whether high temperature limits the occurrence of this species with latitudinal cline. The two sites are well suited to testing this hypothesis as they are characterized by similar chlorophyll a concentration (Chl a) but different temperature [sea surface temperature (SST)]. The abundance of O. similis at L4 was ∼10 times higher than at LTER-MC. Moreover, this species had several peaks of abundance during the year at L4 but a single peak in spring at LTER-MC. The main mode of temporal variability in abundance was seasonal at both sites. The abundance of O. similis was negatively correlated with SST only at LTER-MC, whereas it was positively correlated with Chl a at both sites. Oithona similis had a temperature optimum between 15 and 20°C reaching maximum abundance at ∼16.5°C at LTER-MC, but showed no Chl a optimum at either site. We conclude that the abundance of O. similis increases with prey availability up to 16.5°C and that temperature >20°C represents the main limiting factor for population persistence.

Temporal variations in the life-cycles of aphids (Sternorrhyncha: Aphididae) and their coccinellid predators

Aphids are either monoecious living either on trees or herbaceous plants, or heteroecious, which involves host alternating between a tree (primary host) and a herbaceous plant (secondary host). We described the temporal variations in abundance and richness of aphids in an Algerian orchard, over a 6 month period. We recorded the choice of basin colour, the relative height of traps, and monthly Barycenter of winged populations. We also recorded temporal variations in the structure of ladybird communities. Tree-living species of aphids are the last to be caught with most caught by the yellow traps, possibly because of the predominant greenness of the vegetation in April. Most were also caught by high traps. Their phenology coincides with that of the second peak of ladybirds. In contrast, the phenology of species of aphids living on herbaceous plants differs greatly, which reflects their host plant diversity. In March relatively more of these aphids were caught by the green traps, possibly because at that time the ground was not yet covered by vegetation. Early and late species of aphids are at greater risk of being attacked by ladybirds as they are also most active early and late in the season. The highest catches of the heteroecious species of aphids were recorded in the middle of the trapping period and between those of the two groups of monoecious species of aphids. The adaptive significance of the differences in the behaviour and ecology of the aphids in the three groups is discussed.

Improved state‐space models for inference about spatial and temporal variation in abundance from count data

Models of population dynamics are frequently used for purposes such as testing hypotheses about density dependence and predicting species' responses to future environmental change or conservation actions. Fitting models of population dynamics to field data is challenging because most data sets are characterized by observation error, which can inflate estimates of process variation if ignored. Recently, state‐space models have been developed to deal with this problem by directly modeling both the observation error and the ecological process of interest. Conventional state‐space models, however, have several important limitations: (1) they assume that random effects are Gaussian distributed, which implies that abundance can be negative and that false positive observation errors are equally likely as false negative errors; (2) they do not admit spatial variation in population dynamics; and (3) some of the parameters of the model are not estimable. We demonstrate how each of these problems can be resolved using a class of hierarchical models proposed byDail and Madsen (2011)that attributes observation error to imperfect detection. We expand this class of models to accommodate classical growth models (e.g., exponential and Ricker‐logistic), zero‐inflation, and random effects. We also present methods for forecasting population size under future environmental conditions. Implementation of these ideas is possible using either frequentist or Bayesian methods, as demonstrated by accompanying R and JAGS code. Results of a simulation study suggest that bias is negligible and coverage nominal in most cases for the proposed model extensions. An analysis of data from the North American Breeding Bird Survey highlights how these methods can be readily applied to existing data, but it also suggests that precision will be low when direct information about detection probability (such as is collected using distance sampling or replicated counts) is lacking.

Soil mesofauna effects on litter decomposition in the coniferous forest of the Changbai Mountains, China

Spatial and temporal variations of abundance and community structure of soil fauna have an influence on litter decomposition. In this paper, litterbags with two different mesh sizes (1mm and 0.01mm) were used to exclude soil animals of specific body size. The decomposition of the litter of Abies nephrolepis and Picea jezoensis were examined in the coniferous forest of the Changbai Mountains. In addition, the effect of soil mesofauna and habitat (with different altitudes) on litter decomposition was also determined. It was found that the remaining mass between the 1mm and 0.01mm mesh size litterbags varied significantly among the incubation times. The remaining mass of A. nephrolepis was lower than that of P. jezoensis after one year of decomposition. The elevation gradient had no effect on the litter decomposition. The contribution of soil mesofauna to litter mass loss of P. jezoensis in the lower coniferous forest was higher than that in the upper coniferous forest (p<0.05). Litter species, habitat and incubation time had clear effects on soil mesofauna community composition. The dominant groups of soil mesofauna in the litterbags were Collembola and Acarina, of which the abundances were significantly correlated with the litter mass loss in the 1mm mesh size litterbags at the two sites. Moreover, the litter mass losses were shown to be distinctively related to the richness and abundance of soil mesofauna. However, the Shannon–Wiener index was correlated with the P. jezoensis litter mass loss in the lower coniferous forest. Therefore, it was concluded that the soil mesofauna and litter species clearly impacted the litter decomposition, but the effects of their interactions on the litter decomposition were not significant in the coniferous forest of the Changbai Mountains.

Distribuição espacial e temporal de espécies de Bledius (Coleoptera, Staphylinidae) em praias arenosas no sul do Brasil

Besouros da família Staphylinidae são comuns em zonas costeiras inundáveis pelas marés, como praias arenosas, manguezais, estuários e marismas. O objetivo desse trabalho foi estudar a distribuição espacial e a variação temporal da abundância ao longo de um ano, das espécies ocorrentes em duas praias arenosas (Assenodi e Cem) no Pontal do Paraná, Paraná, Brasil. Coletas semanais com um cilindro de PVC com 15 cm de diâmetro (0,017 m²) enterrado a 5 cm de profundidade, foram realizadas de janeiro a dezembro de 2012. A praia Assenodi apresentou altos valores de umidade de sedimento no supralitoral e pós-praia. Nesta praia, Bledius bonariensis foi dominante, mas também houve registro de B. fernandezi, ambas distribuídas nas porções superiores do perfil praial e ocorreram ao longo de todo o ano. A praia Cem apresentou valores altos de umidade do sedimento apenas no mesolitoral, em decorrência da subida e descida da maré, neste estrato B. hermani, foi a espécie dominante. Bledius bonariensis teve ocorrência ocasional em alguns meses do outono e inverno, associada a um aumento nas precipitações. A variação na abundância de B. hermani foi grande, sendo os maiores valores associados às altas temperaturas do verão. As espécies de Bledius mostraram uma clara separação espacial relacionada a distintos requerimentos ambientais, o que possibilita a coocorrência das três espécies na mesma praia em função de variações ambientais ao longo do ano.

Zooplankton abundance, biomass, and size structure in the coastal waters of the northeastern Mediterranean Sea

Zooplankton was studied seasonally between 2009 and 2011 in Iskenderun Bay in order to determine temporal variations in abundance, biomass, and size structure and their relationships with environmental factors. Zooplankton sampling was performed vertically using a WP-2 net (200-µm). A total of 30 zooplankton taxonomic groups were identified. Cladocera was the dominant group, and together with Copepoda and Appendicularia constituted approximately 90% of zooplankton. In respect to abundance and biomass values, 2 peaks were observed in 2009, the first in spring and the second in autumn. However, a second peak was observed in summer in both 2010 and 2011, due to increases in cladoceran abundance. During all seasons and years of the study period, small-sized organisms (200-500 µm) constituted the majority of the zooplankton. Zooplankton abundance was influenced by environmental factors. The relationship between the abundance of zooplankton groups and environmental parameters varied according to the groups. In conclusion, clear seasonal variation and slight differences among years were observed in terms of the examined properties of the zooplankton groups. Abiotic environmental variables and availability of food were considered to particularly affect this variability.

Spatial and temporal habitat use by white sharks (Carcharodon carcharias) at an aggregation site in southern New Zealand

Subadult and adult white sharks aggregate seasonally near pinniped colonies in several parts of the globe. The time spent there may represent the most vulnerable part of their otherwise migratory life cycle. White sharks have low productivity and may suffer population declines even when afforded legislative protection. White sharks were protected in New Zealand in 2007, but are subject to ongoing incidental fishing mortality. We deployed electronic tags on white sharks at north-eastern Stewart Island in southern New Zealand to identify their temporal and spatial patterns of occupancy, and to inform management measures that aim to separate sharks from fishing effort. White sharks were present almost continuously from late summer to early winter, peaking in autumn (March–June). The population comprised mainly subadult and adult males and subadult females, with males predominating by 2.5:1 during autumn. White shark abundance was greatest in the Titi Islands, and there was fine-scale spatial and temporal variability in abundance. These sharks travel well beyond their aggregation sites, but the behaviour and dynamics of white sharks in other parts of New Zealand remain poorly understood. Any attempts to reduce incidental mortality by protecting white shark habitat must consider a wider spatial context.

Spatial and temporal variations in the abundance, distribution, and aggregation of krill (Thysanoessa raschii and Meganyctiphanes norvegica) in the lower estuary and Gulf of St. Lawrence

The opportunistic collection of hydroacoustic data during multipurpose, large-scale surveys since 2000 has led to the detection of several, newly-documented krill concentrations throughout the Gulf of St. Lawrence. Based on both historical and these recent results, a series of regional-scale acoustic surveys was initiated in the northwestern Gulf and estuary to quantify the spatial and temporal variations in the regional abundance, distribution and aggregation of northern and Arctic krill. By using a recently-developed multi-frequency method to classify these two krill species, our study re-evaluated the species-specific krill distribution and abundance, previously monitored by plankton-net sampling alone. We show that Thysanoessa raschii is the more coastal species, with its center-of-mass in the shelf and slope habitats. Meganyctiphanes norvegica forms generally less dense aggregations in the slope and channel habitats. Biomass in the northwestern Gulf and estuary was split 60:40 between T. raschii and M. norvegica, and totaled 1.0 million tonnes in August 2009; substantially more than has been reported previously. This re-evaluation should have considerable impact on ecosystem models which have assumed much lower values for these important forage populations. The pattern of krill aggregations identified from large- and regional-scale surveys will have important implications for the interpretation of critical habitat for endangered marine mammals which depend on krill.

BACI monitoring of effects of hydraulic dredging for cockles on intertidal benthic habitats of Dundalk Bay, Ireland

Hydraulic dredging for bivalves, such as cockles (Cerastoderma edule), has the potential to cause significant impacts on marine intertidal benthos. Although this fishing activity is common in northern European Natura 2000 sites such impacts may be incompatible with conservation objectives for designated habitats and species within these sites. In 2009–2010 a spatially nested control-impact study was undertaken before (t0), 8–9 days after (t1) and 4 months (t2) following dredging and extraction of 108 tonnes of cockles from a standing stock of 2158 tonnes in Dundalk Bay. This study failed to detect significant effects on benthic sediments, or the overall community structure. However, a fishing effect on the target species C. edule in one sampling area and a short lived effect on the bivalve Angulus tenuis were identified. Significant spatial and temporal variability in abundance of species and taxonomic groups, unrelated to fishing effects, was observed. Previous studies on the effects of fisheries on marine intertidal benthos have reported variable results, related to study design and objectives and the physical characteristics of the study site. Site specific studies, relative to the intensity and frequency of proposed fishing activity, may be required to adequately inform managers whether such activities are compatible with specific conservation objectives for Natura 2000 sites.

Irruptive movements and breeding dispersal of snowy owls: a specialized predator exploiting a pulsed resource

Mobility and irruptive movements have been proposed as mechanisms that could allow some diet specialists to inhabit and breed in environments with highly unpredictable resources, like the arctic tundra. The snowy owl, one of the main avian predators of the tundra, is known to specialize on lemmings during the breeding season. These small mammals are also well known for their tremendous spatial and temporal variations in abundance. We examined the spring (pre‐breeding, from March to June) movements of snowy owls by tracking 9 breeding females in the Canadian Arctic for up to 3 yr with satellite transmitters. We used state‐space modeling to assess searching behavior and measure breeding dispersal distances. We also ascertain lemming abundance at some of the sites used by the marked owls. Tracked owls displayed searching movements for extended periods (up to 108 d) and traveled over large distances (up to 4093 km) each spring. The distance between furthest apart searching areas in a given year averaged 828 km (range 220 to 2433 km). Settlement date, distance between searching areas, traveled distance and the duration of prospecting movements were longer in the year where density of lemmings recorded in the eastern High‐Arctic (Bylot Island) was lowest. Nonetheless, snowy owls settled in areas where local lemming abundance was relatively high. Individual breeding dispersal distance between consecutive years averaged 725 km (range 18 to 2224). Overall, the high mobility of female snowy owls allowed these diet specialists to behave as irruptive migrants and to sustain their reproductive activities during consecutive years even under highly fluctuating resources.

Spatial and temporal heterogeneity in the distribution of an Antarctic amphipod and relationship with the sediment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 502:169-183 (2014) - DOI: https://doi.org/10.3354/meps10715 Spatial and temporal heterogeneity in the distribution of an Antarctic amphipod and relationship with the sediment Helena P. Baird1,2,*, Jonathan S. Stark1 1Terrestrial and Nearshore Ecosystems Theme, Australian Antarctic Division, Kingston, Tasmania 7050, Australia 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania 7001, Australia *Corresponding author: hpbaird@utas.edu.au ABSTRACT: The nearshore Antarctic environment is subject to increasing anthropogenic impact, yet the ecological processes influencing some of its most dominant species remain poorly understood. We examined patterns of the distribution and abundance of the Antarctic amphipod Orchomenella franklini in relation to the local environment. Samples of benthic sediment were collected in East Antarctica across several spatial and temporal scales and were analysed for the abundance of O. franklini and various sediment properties. O. franklini was found to reach extremely high densities (>41000 m-2), yet abundance was strongly heterogeneous on all spatial scales tested. Temporal variation in abundance was also significant and was location-specific, potentially reflecting fluctuations in food supply and variable conditions resulting from ice disturbance. Principal component analysis and generalised additive modelling revealed evidence of a relationship between the distribution of O. franklini and the sediment, which was consistent with its deposit-feeding trophic niche. Generally, the abundance of O. franklini increased with decreasing sediment grain size and increasing trace element concentration. Abundance also peaked at high (though not maximum) total organic carbon content. This is one of the first empirical demonstrations of a correlation between discrete physical sediment traits and the abundance of an infaunal benthic species in the Antarctic, with evidence consolidated from 2 geographic regions. The influence of local conditions on the abundance of O. franklini provides insight on the heterogeneity of Antarctic benthic ecosystems. KEY WORDS: Benthic sediment · Peracarid crustacean · Population density · Metals · Grain size · Anthropogenic impact · Environmental change Full text in pdf format Supplementary material PreviousNextCite this article as: Baird HP, Stark JS (2014) Spatial and temporal heterogeneity in the distribution of an Antarctic amphipod and relationship with the sediment. Mar Ecol Prog Ser 502:169-183. https://doi.org/10.3354/meps10715 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 502. Online publication date: April 15, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Experimental decoupling of canopy opening and debris addition on tropical gastropod populations and communities

Climate-induced disturbances such as hurricanes affect the structure and functioning of many ecosystems, especially those in the Caribbean Basin, where effects are well documented with regard to biodiversity and biogeochemical dynamics. Because climate change will likely alter the frequency or intensity of such storms, it is increasingly important to understand the mechanistic bases for ecosystem responses. However, this is particularly difficult to do in the absence of manipulative experiments that decouple confounded factors such as canopy opening and debris deposition. To address this issue, we exploited a replicated factorial design to experimentally distinguish the effects of canopy opening and debris deposition on population- and community-level characteristics of gastropods in the Luquillo Experimental Forest of Puerto Rico. Despite considerable spatial variation, abundances of all gastropods (combined) as well as abundances of each of 3 species (i.e., Alcadia striata, Platysuccinea portoricensis, and Polydontes acutangula) responded significantly to canopy opening while abundances of each of 2 species (i.e., Pl. portoricensis, and Po. acutangula) responded significantly to debris deposition within two years of experimental manipulation. In contrast, two species (i.e., Gaeotis nigrolineata and Nenia tridens) did not respond to any experimental manipulations in the short term. Moreover, species composition did not differ between pre- and post-manipulation periods, in part because of considerable variation among replicated blocks. In contrast, canopy removal consistently affected species richness, Shannon diversity, and rarity, while debris deposition consistently affected species richness and Shannon diversity. Neither treatment affected species dominance or evenness. Longer-term responses of the gastropod fauna were more complex. Although considerable interspecific heterogeneity characterized responses of the gastropod fauna, temporal variation in mean abundance for each of the three manipulative treatments was similar to that of the non-manipulated treatment when abundances were combined for all species. In contrast, temporal variation in each of the manipulative treatments was unrelated to temporal variation in the non-manipulated treatment for species richness, evenness, dominance, and rarity. Moreover, temporal variation in abundance generally differed between at least two of the manipulative treatments for most species and temporal variation in components of taxonomic biodiversity generally differed between manipulative treatments as well. Temporal variation in species composition was considerable and comparable for each of the four treatment combinations. Species composition within each treatment combination varied over time in ways unrelated to temporal variation in the other treatment combinations, including the reference treatment (i.e., no canopy trimming and no debris addition). Manipulated treatments were surrounded by large areas of intact forest, and tabonuco forest generally exhibits appreciable spatial and temporal variation. Natural spatiotemporal variation in the study system likely overwhelmed many of the effects of experimental manipulations on gastropod populations or communities via edge effects and recruitment of individuals from nearby less disturbed portions of the landscape.

Intermittent recruitment and exploitation pulse underlying temporal variability in a demersal deep-water fish population

Abstract Recent temporal variability in abundance, size and age structure, distribution, and recruitment of the Skagerrak population of the commercially exploited long-lived deep-water demersal macrourid roundnose grenadier (Coryphaenoides rupestris) appeared strongly influenced by a combined effect of a single pronounced recruitment incident in the early 1990s and a subsequent pulse in targeted exploitation a decade later. Fishery-independent annual survey data showed that probably only one strong year class occurred across an almost three-decade period, 1985–present. Recruitment studies in deep-water fish remain few, yet rarity of successful recruitment events may have to be added to life-history characteristics already recognized as limiting the potential for sustainable harvesting of deep-water demersal fish, i.e. extended lifespan, slow growth, high age at first maturity, and low fecundity.