Seasonal Changes In Distribution Research Articles

Effect of seasonal distribution in precipitation on soil nitrogen mineralization in a subtropical forest

Soil N mineralization is a key process of nutrient cycling in ecosystems. The mechanism of the seasonal distribution of precipitation on soil N mineralization remains unclear. We conducted a precipitation manipulation experiment in a subtropical forest in the middle and lower reaches of the Yangtze River in China from 2020 to 2022, with three treatments, including control (CK), decreased precipitation in the dry season with extremely increased precipitation in the wet season (T1), and decreased precipitation in the dry season with proportionally increased precipitation in the wet season (T2). With in situ resin core method, we explored the effect of seasonal distribution of precipitation on soil N mineralization. The results showed that T1 and T2 significantly decreased dry season net nitrification rate by 57.9% and 72.5% and the net N mineralization rate by 82.5% and 89.6%, respectively, and significantly increased wet season net nitrification rate by 64.3% and 79.5% and net N mineralization rate by 64.2% and 81.1%, respectively. Proportionally increased precipitation in the wet season was more conducive to soil N mine-ralization process than extremely increased precipitation in the wet season. Results of the structural equation model showed that change in seasonal distribution of precipitation could significantly affect soil N mineralization processes in the subtropical forest by changing soil water content, ammonium nitrogen, microbial biomass nitrogen, and soil C:N. Our results had important reference for understanding soil nitrogen cycling and other ecological processes, and were conducive to more accurate assessment on the impacts of future changes in seasonal precipitation pattern on subtropical forest ecosystems.

Assessment of the spatiotemporal risk of avian influenza between waterfowl and poultry farms during the annual cycle: A spatial prediction study focused on seasonal distribution changes in resident waterfowl in South Korea.

Previous studies and efforts to prevent and manage avian influenza (AI) outbreaks have mainly focused on the wintering season. However, outbreaks of AI have been reported in the summer, including the breeding season of waterfowl. Additionally, the spatial distribution of waterfowl can easily change during the annual cycle due to their life-cycle traits and the presence of both migrants and residents in the population. Thus, we assessed the spatiotemporal variation in AI exposure risk in poultry due to spatial distribution changes in three duck species included in both major residents and wintering migrants in South Korea, the mandarin, mallard and spot-billed duck, during wintering (October-March), breeding (April-June) and whole annual seasons. To estimate seasonal ecological niche variations among the three duck species, we applied pairwise ecological niche analysis using the Pianka index. Subsequently, seasonal distribution models were projected by overlaying the monthly ranges estimated by the maximum entropy model. Finally, we overlaid each seasonal distribution range onto a poultry distribution map of South Korea. We found that the mandarin had less niche overlap with the mallard and spot-billed duck during the wintering season than during the breeding season, whereas the mallard had less niche overlap with the mandarin and spot-billed duck during the breeding season than during the wintering season. Breeding and annual distribution ranges of the mandarin and spot-billed duck, but not the mallard, were similar or even wider than their wintering ranges. Similarly, the mandarin and spot-billed duck showed more extensive overlap proportions between poultry and their distributional ranges during both the breeding and annual seasons than during the wintering season. These results suggest that potential AI exposure in poultry can occur more widely in the summer than in winter, depending on sympatry with the host duck species. Future studies considering the population density and variable pathogenicity of AI are required.

Seasonal changes in distribution and abundance of a local Corncrake population

Many bird species have experienced short- or long-term population declines. However, the mechanisms and reasons underlying such negative changes are often not fully understood, making it difficult to identify effective conservation measures to recover populations. In this study, we focused on local changes in the abundance and distribution of calling male Corncrakes Crex crex in relation to: (1) within- and between-season site fidelity of adult males, (2) spatial distribution of territories in consecutive years and (3) the effect of habitat conditions on population size. We counted the number of calling males at ten randomly selected study plots (1 km2) in 2014–2018. Additionally, males were caught and individually marked in years 2015–2017. We found significant between-year changes in Corncrake abundance, from a 34% decrease to a 21% increase. On average, 32% of males established territories in the same locations as males recorded in the previous year. Breeding site fidelity was very low, with only 2–5% of males recaptured in the following year. Males selected areas characterized by higher values of NDVI (Normalized Difference Vegetation Index–higher values indicate more biomass) than on average within the study area. Population size in a particular year was significantly affected by the NDVI of the previous year but not by the NDVI in the current breeding season. We suppose that Corncrakes may exhibit a nomadic breeding behavior, and settle at territories when they encounter optimal habitat conditions. Moreover, as population size was negatively correlated with habitat conditions at the beginning of the previous breeding season, we suppose that local population changes may reflect more general trends in a whole population rather than local breeding success. Therefore, we highlight the need for better knowledge of Corncrake dispersal within the main European population and for the coordination of monitoring and conservation efforts, especially in those regions where most Corncrakes breed.

Local and Regional Indian Summer Monsoon Precipitation Dynamics During Termination II and the Last Interglacial

AbstractTo date Indian summer monsoon (ISM) dynamics have been assessed by changes in stalagmite δ18O. However, stalagmite δ18O is influenced by multiple environmental factors (e.g., atmospheric moisture transport, rainfall amount at the study site, and ISM seasonality), precluding simple and clear reconstructions of rainfall amount or variability. This study aims to disentangle these environmental factors by combining δ18O, δ44Ca, and elemental data from a stalagmite covering Termination II and the last interglacial from Mawmluh Cave, NE India, to produce a semiquantitative reconstruction of past ISM rainfall. We interpret δ18O as a mixed signal of rainfall source dynamics and rainfall amount and coupled δ44Ca and X/Ca ratios as indicators of local infiltration rate and prior calcite precipitation in the karst zone. The wettest conditions in our studied interval (135 and 100 kyrs BP; BP = before present, with the present being 1950 CE) occurred during Marine Isotope Stage 5e. Our multiproxy data set suggests a likely change in seasonal distribution of Marine Isotope Stage 5e rainfall compared to the Holocene; the wet season was longer with higher‐than‐modern dry season rainfall. Using the last interglacial as an analogue for future anthropogenic warming, our data suggest a more erratic ISM behavior in a warmer world.

Correlation of changes in seasonal distribution and catch of red sea bream Pagrus major with winter temperature in the eastern Seto Inland Sea, Japan (1972–2010)

AbstractRed sea bream Pagrus major is a commercially important fish in Japan. In eastern Seto Inland Sea (SIS), the catch has increased from 297 tons in 1972 to 2,039 tons in 2010. We examined the relationship, 1972–2010, between increase in catch and winter temperature, based on the catch in February and March and the lowest water temperature at 10 m depth. In 1972–1986, the lowest water temperatures in the inner SIS areas (Osaka Bay, Harima‐nada, and Bisan‐seto) were <8°C, which is physiologically unfavorable for red sea bream. However, in 1987–2010 temperatures were generally ≥8°C. In the inner areas, the catch during winter had been minimal until the early 1980s, presumably because most red sea breams moved to the Kuroshio‐influenced (warmer) Kii Channel area. However, the winter catch in the inner areas of SIS increased from the late 1980s with warm winters. In addition, the catch between April and June, the spawning season, increased in the inner areas from the 1990s, and the catch rate of the inner areas was more than twice higher in the 2000s than in the 1980s. The results suggest that expansion of the distribution area during winter due to warm winter and increase in egg production in the inner areas greatly contributes to the increasing in catch in the eastern SIS.

Trophic Ecology of Lahontan Cutthroat Trout: Historical Predator–Prey Interaction Supports Native Apex Predator in a Unique Desert Lake

AbstractPyramid Lake, Nevada, remains one of the last strongholds for lacustrine‐strain Lahontan Cutthroat Trout Oncorhynchus clarkii henshawi (LCT) following historical declines throughout their native range. Historically the apex predator in this aquatic ecosystem, LCT in Pyramid Lake are now entirely dependent on hatchery programs and are potentially threatened by the introduction of a nonnative piscivore. The purpose of this study was to identify strong food web interactions and potential trophic limitations to the LCT population. Our specific objectives were to estimate seasonal foraging patterns, trophic position (TP), trophic niche space, diet composition, and seasonal depth distributions of LCT relative to prey fish. Additionally, we evaluated the potential for competition between LCT and nonnative, piscivorous Sacramento Perch Archoplites interruptus by examining diet overlap and trophic niche space. Our results indicate that LCT are apex predators, with TP (large [>400 mm TL] LCT: TP [mean ± 1.96·SE] = 4.30 ± 0.04) and diet composition indicating high rates of piscivory (average annual rate of piscivory = 77.1% for large LCT) throughout the year. Small (200–400 mm TL) LCT exhibited weak dietary overlap (Schoener's index = 0.55) and large LCT exhibited strong overlap (Schoener's index = 0.72) with Sacramento Perch. These trends were present despite seasonal changes in distribution and catch of Tui Chub Siphateles bicolor, the primary prey of LCT. Analysis of isotopic niche space also indicated strong overlap between the trophic niche of large LCT (89%) and that of Sacramento Perch; however, overall catch rates of Sacramento Perch were low. Despite the presence of a potential nonnative competitor, LCT demonstrate high rates of piscivory and are not negatively influenced by Sacramento Perch. Overall, these results demonstrate how trophic niche ecology can be used to evaluate key food web interactions in anthropogenically altered ecosystems.

Waterbirds Alter their Distribution and Behavior in the Presence of Bald Eagles (Haliaeetus leucocephalus)

Abstract We explored changes in seasonal distribution and behavior of waterbirds in the Strait of Georgia, Canada, in response to increased presence of a major avian predator, the Bald Eagle (Haliaeetus leucocephalus). Eagles were widespread and their increase through fall and winter coincided with migratory movements of waterbirds. Many species of waterbird used inshore waters in early fall when eagles were scarce. Diving birds moved away from inshore waters when eagles returned in late fall and winter, whereas dabbling ducks formed large flocks in inshore waters and spent proportionally more time being vigilant as winter progressed. Flock sizes and avoidance flight distances of scoters and dabblers, but not gulls, increased with proximity to eagles. Waterbirds did not alter vigilance with distance to eagles. We discuss our findings in context of management issues regarding apparent declines and importance of understanding indirect effects of predators on prey for wildlife monitoring.

Physiological homeostasis and morphological plasticity of two tree species subjected to precipitation seasonal distribution changes

General circulation models and empirical observations show that rainfall patterns will become increasingly erratic in the future as the paradigm “dry gets drier, wet gets wetter” becomes globally prevalent. Currently, few field studies have evaluated the long-term effects of extreme precipitation on forest ecosystems based on tree physiology. To provide a better mechanistic understanding of these effects, a two-year “Precipitation Seasonal Distribution Changes” experiment (PSDC) was conducted in lower subtropical China. The treatments included “Drier dry season and wetter wet season (DD)”, ‘Extended dry season and wetter wet season (ED)” and “Ambient control (AC)’. The throughfall of the DD treatment was excluded during the dry season (October-March of the following year) to simulate drought, whereas the throughfall of the ED treatment was excluded in the spring (April-May) to simulate spring drought without significant altering the total annual precipitation input. The sap flow, water use efficiency, leaf and wood nutrient content and morphological parameters of two co-occurring tree species, Michelia macclurei Dandy and Schima superba Gardner & Champ., were quantified to elucidate the physiological mechanisms that occur in response to rainfall pattern changes. Our results indicated that the whole-tree transpiration per unit sapwood area (Js) and intrinsic water use efficiency (WUEi) showed homeostatic responses. Tree transpiration and response parameters to environmental variables (vapor pressure deficit [VPD] and photosynthetically active radiation [PAR]) did not show significant treatment effects regardless of drought, spring drought or irrigation periods. However, the leaf nitrogen (Narea) and phosphorus (Parea) content showed fluctuations, particularly the leaf N:P ratio, which showed that rainfall pattern changes had adverse effects on nutrient acquisition in this dual nitrogen- and phosphorus- limited forest ecosystem. The wood stoichiometry was more conserved than the leaf stoichiometry. For a given leaf 13C discrimination (≈ci/ca), the wood 13C discrimination did not show treatment or species effects, suggesting that the carbon transfer of trees was not affected by rainfall patterns. The branch As:Al was significantly negatively correlated with the parameters representing the sensitivity of tree transpiration to VPD, indicating that the trees maintained homeostatic responses by combining stomatal control and morphological adjustments. In mesic environments, the two studied tree species showed high resilience to seasonal rainfall pattern changes and homeostatic responses to nutrient acquisition, light use and water uptake, which is consistent with the ‘ecohydrological equilibrium theory’. In conclusion, the shallow-rooted M. macclurei presented a growth advantage in mesic environments or under mild water stress, whereas the deeply rooted S. superba is more competitive under predicted prolonged drought scenarios, such as DD and ED rain patterns, because of its greater morphological plasticity and increased water uptake from groundwater. Both species are common in south and eastern China but present inherently different responses to seasonal precipitation changes, which implies that changes in the timing and magnitude of precipitation may have consequences for plant nutrient acquisition and water balance and the potential to alter community composition.

Anomalous ecosystem dynamics following the apparent collapse of a keystone forage species

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 553:185-202 (2016) - DOI: https://doi.org/10.3354/meps11761 Anomalous ecosystem dynamics following the apparent collapse of a keystone forage species Kenneth T. Frank1,2,*, Brian Petrie1, Daniel Boyce2, William C. Leggett2 1Fisheries and Oceans Canada, Bedford Institute of Oceanography, Ocean Sciences Division, Dartmouth, Nova Scotia B2Y 4A2, Canada 2Department of Biology, Queen’s University, Kingston, Ontario K7L 3N6, Canada *Corresponding author: kenneth.frank@dfo-mpo.gc.ca ABSTRACT: Major groundfish populations in the western Atlantic north of Georges Bank/Western Scotian Shelf experienced near-total population collapses beginning in the late 1980s-early 1990s. Explosive increases in the abundance of their pelagic fish and invertebrate prey (notably capelin, sand lance, herring, shrimp and snow crab) generally followed. However, several investigators have concluded, based on the results of annual acoustic surveys, that the lightly exploited capelin stock in the Newfoundland/Labrador (NL) region experienced a sudden 6.8 Mt (98%) decline in biomass from 1990 to 1991 coincident with the groundfish collapse. Given the enormity, duration and unexpected nature of this decline, it was characterized as a collapse. The contrasting response of this capelin stock to the groundfish collapse relative to other North Atlantic (NA) ecosystems prompted us to undertake systematic analyses of the NL ecosystem. The reported capelin collapse in NL should have induced significant responses of trophically linked species, as have been reported in other NA ecosystems. We found little evidence of changes in the population abundance, diet and condition of marine mammals, cod, seabirds and zooplankton, in indexes of the areal occupancy and spawning biomass of capelin, or of environmental effects. These results strongly support the hypothesis that the reported collapse did not occur. Profound seasonal distribution changes, a fixed in time and space acoustic survey in a restricted portion of the distributional range of capelin, and the possibility that NL capelin stock has become less migratory provide a more robust and consistent explanation of the observations. KEY WORDS: Forage fish · Stock collapse · Ecosystem response · North Atlantic · Acoustic surveys · Migration Full text in pdf format Supplementary material PreviousNextCite this article as: Frank KT, Petrie B, Boyce D, Leggett WC (2016) Anomalous ecosystem dynamics following the apparent collapse of a keystone forage species. Mar Ecol Prog Ser 553:185-202. https://doi.org/10.3354/meps11761 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 553. Online publication date: July 14, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Seasonal migration of the starry smooth-hound shark Mustelus asterias as revealed from tag-recapture data of an angler-led tagging programme.

The primary aim of this long-term angler-led tagging programme was to gain information about seasonal changes in distribution of the starry smooth-hound shark Mustelus asterias, along the Dutch coast for management and conservation purposes. Between 2011 and 2014, M. asterias comprised 92·6% (n = 2418) of the total elasmobranch catch (n = 2612) by the licenced group of taggers within the Dutch Delta of which 2244 M. asterias were fin-tagged with plastic rototags. Sex and total length (LT ) composition inside the eastern tidal basin (Oosterschelde) were significantly different, i.e. more females and larger individuals, than outside indicating a pupping ground, which was confirmed by the capture of 30 newborn pups (≤32 cm). The distribution pattern of reported recaptured M. asterias (return-rate 3·6%, n = 80) showed a circannual migration between summering in the southern North Sea and wintering in the English Channel and the Bay of Biscay, and suggests that M. asterias is philopatric. The Dutch angling season for M. asterias runs from approximately mid-May to mid-October when the water temperature is above 13° C. Recaptures of eight mature females, but no males in the Bay of Biscay, indicate partial spatial segregation by sex, where mature females migrate over larger distances than immature females and males. These observations, with the absence of recaptures in other known summering areas (i.e. the Irish Sea and Bristol Channel), suggest that the southern North Sea is used by a separate population. Implications for management and recommendations to improve and expand the study approach are discussed.

Peary caribou distribution within the Bathurst Island Complex relative to the boundary proposed for Qausuittuq National Park, Nunavut

How caribou (Rangifer tarandus), including Peary caribou (R. t. pearyi), use their annual ranges varies with changes in abundance. While fidelity to some seasonal ranges is persistent, use of other areas changes. Consequently, understanding changes in seasonal distribution is useful for designing boundaries of protected areas for caribou conservation. A case in point is the proposed Qausuittuq (Northern Bathurst Island) National Park for Bathurst Island and its satellite islands in the High Arctic of Canada. Since 1961, Peary caribou have been through three periods of high and low abundance. We examined caribou distribution and composition mapped during nine systematic aerial surveys (1961–2013), unsystematic helicopter surveys (1989–98), and limited radio-collaring from 1994–97 and 2003–06. While migration patterns changed and use of southern Bathurst Island decreased during lows in abundance, use of satellite islands, especially Cameron Island for winter range, persisted during both highs and lows in abundance. The northeast coast of Bathurst Island was used to a greater extent during the rut and during summer at low abundance. We suggest that Park boundaries which include Cameron Island and the northeast coast of Bathurst Island will be more effective in contributing to the persistence of Peary caribou on the Bathurst Island Complex.

Rainfall and runoff regime trends in mountain catchments (Case study area: the upper Hron River basin, Slovakia)

Abstract This paper presents an analysis of trends and causes of changes of selected hydroclimatic variables influencing the runoff regime in the upper Hron River basin (Slovakia). Different methods for identifying trends in data series are evaluated and include: simple mass curve analysis, linear regression, frequency analysis of flood events, use of the Indicators of Hydrological Alteration software, and the Mann-Kendall test. Analyses are performed for data from two periods (1931-2010 and 1961-2010). The changes in runoff are significant, especially in terms of lower QMax and 75 percentile values. This fact is also confirmed by the lower frequency and extremity of flood events. The 1980s are considered a turning point in the development of all hydroclimatic variables. The Mann-Kendall test shows a significant decrease in runoff in the winter period. The main causes of runoff decline are: the considerable increase in air temperature, the decrease in snow cover depth and changes in seasonal distribution of precipitation amounts.

Environment-driven changes in terrestrial habitat use and distribution of the Galapagos sea lion

Understanding habitat use patterns of marine apex predators is of paramount impor- tance for the effective design of conservation plans. Due to their amphibious life cycle, pinnipeds are one of the most vulnerable groups to habitat loss and degradation. Reducing knowledge gaps that still exist regarding temporal changes in tropical pinniped habitat use is therefore of particu- lar importance for conservation efforts. We analyzed terrestrial habitat use phenology of a tropical otariid, the Galapagos sea lion Zalophus wollebaeki. Regular land-based censuses were carried out in Wreck Bay of San Cristobal Island, Galapagos, between 2008 and 2012 to explore seasonal changes in sea lion abundance, distribution, and preferences among different habitat types. A daily cycle of haul-out patterns was observed. Animals aggregated on sandy beaches during the coldest periods of the day and were more abundant on rocky and artificial structures when air temperature was warmer. The use of artificial floating platforms as resting places by Z. wollebaeki was described for the first time and linked to environmental variability, suggesting that this may be a successful management tool for pinnipeds inhabiting low latitudes. Further, this species demonstrated seasonal distribution changes, aggregating in high densities during warm seasons and maintaining more even distributions during cold seasons. Sea surface temperature, air tem- perature, and the onset of the breeding season were the variables that most significantly influ- enced haul-out patterns of Z. wollebaeki, indicating that this species can adapt to changing envi- ronmental conditions by displaying a high degree of plasticity regarding its distribution and terrestrial microhabitat preferences.

Zooplankton in Bosten Lake: community characteristics and seasonal changes in distribution

Zooplankton in Bosten Lake: community characteristics and seasonal changes in distribution

Bio‐energetics underpins the spatial response of North Sea plaice (Pleuronectes platessa L.) and sole (Solea solea L.) to climate change

AbstractClimate change is currently one of the main driving forces behind changes in species distributions, and understanding the mechanisms that underpin macroecological patterns is necessary for a more predictive science. Warming sea water temperatures are expected to drive changes in ectothermic marine species ranges due to their thermal tolerance levels. Here, we develop a mechanistic tool to predict size‐ and season‐specific distributions based on the physiology of the species and the temperature and food conditions in the sea. The effects of climate conditions on physiological‐based habitat utilization was then examined for different size‐classes of two commercially important fish species in the North Sea, plaice, Pleuronectes platessa, and sole, Solea solea. The two species provide an attractive comparison as they differ in their physiology (e.g. preferred temperature range). Combining dynamic energy budget (DEB) models with the temperature and food conditions estimated by an ecosystem model (ERSEM), allowed spatial differences in potential growth (as a proxy for habitat quality) to be estimated for 2 years with contrasting temperature and food conditions. The resulting habitat quality maps were in broad agreement with observed ontogenetic and seasonal changes in distribution as well as with the recent changes in distribution which could be attributed to an increase in coastal temperatures. Our physiological‐based model provides a powerful tool to explore the effect of climate change on the spatio‐temporal fish dynamics, predict effects of local or broad‐scale environmental changes and provide a physiological basis for observed changes in species distributions.

Seasonal changes in depth distribution of salmon sharks (Lamna ditropis) in Alaskan waters: implications for foraging ecology

The salmon shark, Lamna ditropis, is an endothermic, apex predator in the productive waters of the Gulf of Alaska (GOA). To understand their role in these productive habitats and to identify and better understand their interactions with commercially important species and fisheries, detailed information regarding the distribution of the salmon shark is required. Archival data records from eight recovered pop-up archival transmitting (PAT) tags were analyzed to examine the geographic and vertical distribution of female salmon sharks and elucidate how their distribution changes in relation to the biotic and abiotic environment. Tagged sharks used the neritic habitats of the GOA for the duration of the PAT deployments. Sharks exhibited a diel periodicity in their dive behavior. Salmon sharks exhibited three different patterns of depth distribution (behavioral modes) that occurred during distinct oceanographic seasons, likely reflecting changes in their foraging ecology in response to seasonal changes in the distribution and availability of important prey. The distribution of salmon sharks in the GOA appears to follow consistent patterns and has a high degree of geographical and vertical overlap with commercially important prey species. This information increases our understanding of interactions between salmon sharks and commercial fisheries and may assist in fostering responsible management for this species.

Climate change impact on the hydrology of Spencer Creek watershed in Southern Ontario, Canada

Summary This study is for the assessment of climate change impact on the future hydrology of Spencer Creek watershed located in Southern Ontario, Canada under the A2 scenario of the Special Report on Emissions Scenarios (SRES). The study is particularly concerned with changes in the climate variables and the seasonal and interannual flow regimes of the study area. The analysis also addresses the annual exceedance probability of extreme precipitation, temperature and flow events. Potential hydrologic effects of climate change were assessed for the Spencer Creek by imposing changes in precipitation and temperature derived from the North American Regional Climate Change Assessment Program (NARCCAP) climate simulations between 2040 and 2069. The climate models results were used as input to three hydrological models to produce projections of Spencer Creek watershed discharges. The results were compared to the observed discharges between 1989 and 2008. Notwithstanding the variability between the different regional climate model and hydrological model projections that envelop the future climate scenarios and the hydrological modeling uncertainties, all future simulations show an increase in the average interannual discharge, but also a noteworthy change in the seasonal distribution of the discharges. While the former is mainly attributed to the average annual precipitation, which tends to increase, the change in seasonal distribution of discharges is in line with the temperature increase of the winter and spring seasons that results in earlier snowmelt. Important changes were found in the annual exceedance probability (recurrence interval) of the extreme precipitation, temperature and runoff events.

New aerial survey and hierarchical model to estimate manatee abundance

AbstractMonitoring the response of endangered and protected species to hydrological restoration is a major component of the adaptive management framework of the Comprehensive Everglades Restoration Plan. The endangered Florida manatee (Trichechus manatus latirostris) lives at the marine‐freshwater interface in southwest Florida and is likely to be affected by hydrologic restoration. To provide managers with prerestoration information on distribution and abundance for postrestoration comparison, we developed and implemented a new aerial survey design and hierarchical statistical model to estimate and map abundance of manatees as a function of patch‐specific habitat characteristics, indicative of manatee requirements for offshore forage (seagrass), inland fresh drinking water, and warm‐water winter refuge. We estimated the number of groups of manatees from dual‐observer counts and estimated the number of individuals within groups by removal sampling. Our model is unique in that we jointly analyzed group and individual counts using assumptions that allow probabilities of group detection to depend on group size. Ours is the first analysis of manatee aerial surveys to model spatial and temporal abundance of manatees in association with habitat type while accounting for imperfect detection. We conducted the study in the Ten Thousand Islands area of southwestern Florida, USA, which was expected to be affected by the Picayune Strand Restoration Project to restore hydrology altered for a failed real‐estate development. We conducted 11 surveys in 2006, spanning the cold, dry season and warm, wet season. To examine short‐term and seasonal changes in distribution we flew paired surveys 1–2 days apart within a given month during the year. Manatees were sparsely distributed across the landscape in small groups. Probability of detection of a group increased with group size; the magnitude of the relationship between group size and detection probability varied among surveys. Probability of detection of individual manatees within a group also differed among surveys, ranging from a low of 0.27 on 11 January to a high of 0.73 on 8 August. During winter surveys, abundance was always higher inland at Port of the Islands (POI), a manatee warm‐water aggregation site, than in the other habitat types. During warm‐season surveys, highest abundances were estimated in offshore habitat where manatees forage on seagrass. Manatees continued to use POI in summer, but in lower numbers than in winter, possibly to drink freshwater. Abundance in other inland systems and inshore bays was low compared to POI in winter and summer, possibly because of low availability of freshwater. During cold weather, maps of patch abundance of paired surveys showed daily changes in manatee distribution associated with rapid changes in air and water temperature as manatees sought warm water with falling temperatures and seagrass areas with increasing temperatures. Within a habitat type, some patches had higher manatee abundance suggesting differences in quality, possibly due to freshwater flow. If hydrological restoration alters the location of quality habitat, postrestoration comparisons using our methods will document how manatees adjust to new resources, providing managers with information on spatial needs for further monitoring or management. Total abundance for the entire area was similar among survey dates. Credible intervals however were large on a few surveys, and may limit our ability to statistically detect trends in total abundance. Additional modeling of abundance with time‐ and patch‐specific covariates of salinity, water temperature, and seagrass abundance will directly link manatee abundance with physical and biological changes due to restoration and should decrease uncertainty of estimates. © 2011 The Wildlife Society.

210 17～20世紀の北アメリカにおける出生季節分布の変動

210 17～20世紀の北アメリカにおける出生季節分布の変動

Seasonal changes in distribution of Hector's dolphin at Banks Peninsula, New Zealand: implications for protected area design

Abstract The efficacy of protected areas for wildlife management is largely dependent on appropriate design. It is therefore crucial that the distribution of target species is well understood. The Banks Peninsula Marine Mammal Sanctuary (BPMMS) was designed to protect Hector's dolphins from bycatch in gillnets. However, the Banks Peninsula dolphin population is likely to be still declining, partly due to continued bycatch outside the boundaries of the BPMMS. A three year series of aerial line‐transect surveys around Banks Peninsula was carried out to investigate seasonal changes in distribution of Hector's dolphins out to 20 nautical miles (37 km) from the coast. Dolphin sightings were concentrated close to shore in shallow water in summer, but were more evenly distributed throughout the study area in winter. A greater proportion of dolphins were sighted outside the 4 nautical miles (7.4 km) offshore boundary of the BPMMS in winter (mean=56%) than in summer (mean=19%) (G=88.25, df=1, P<0.001). Partial Mantel tests revealed the effects of distance offshore and depth on dolphin occurrence while controlling for spatial autocorrelation and multicollinearity within the data. Distance offshore had the strongest and most consistent effect on dolphin presence, while depth had a strong effect in summer only. It is proposed that restrictions on gillnetting around Banks Peninsula must be extended in order to reduce bycatch of Hector's dolphins to a sustainable level, and that a new offshore boundary of the BPMMS would be best defined by distance from the coast. Copyright © 2009 John Wiley & Sons, Ltd.