Spatial Differences In Abundance Research Articles

Contrasting late season pest insect abundance in non‐crop vegetation areas and nearby canola fields in the Canadian Prairies

Abstract Non‐crop vegetation areas in agricultural landscapes are vital for maintaining biodiversity. However, they potentially host pest insects, which can cause economic loss in crop fields. Some insect species have been found to spill into crops from these areas, but this varies depending on species, landscape composition and the time of the season. To determine if five common pest insects of canola crops were spilling into fields during the late growing season, we collected samples at various distances from non‐crop areas, in a part of the Canadian Prairies (Alberta, Canada) where this crop is widely grown. Sampling occurred at 15 sites in each of 10 fields (N = 150 sites). We modelled changes in pest abundance over distance from the non‐crop areas and contrasted the abundance of each taxon in the crop and non‐crop areas. Only leafhoppers (Hemiptera: Cicadellidae) demonstrated a declining gradient in abundance that is consistent with spillover from non‐crop vegetation areas into the canola fields. Weevils were found to have significantly higher abundance in the non‐crop areas, indicating a relationship between this taxon and the non‐crop area in the late season, but there was no decline in abundance, which might indicate spillover occurring. All taxa demonstrated spatial differences in abundance among fields. This study found limited evidence that the pests are spilling over from non‐crop vegetation into canola crops during the late season. Therefore, movement of pests from non‐crop vegetation areas at this time is unlikely to be a driver of pest pressure for this economically important crop.

Post-settlement abundance, condition, and survival in a climate-stressed population of Pacific cod

The Pacific cod (Gadus macrocephalus) fishery recently collapsed in the Gulf of Alaska after a series of marine heatwaves that began in 2014. To gauge the likelihood of population recovery following these extreme warming events, we investigate potential thermal stress on age-0 cohorts through a comprehensive analysis of juvenile cod abundance, condition, growth, and survival data collected from 15 years of beach seine surveys. Abundance was strongly negatively related to ocean temperature during the egg and larval phase (winter–spring), but age-0 cod were larger in the early summer following warm winter–spring temperatures. Body condition indices suggest that warm summers may improve energetic reserves prior to the first winter; however, there was no summer temperature effect on post-settlement growth or survival. Spatial differences in abundance, condition, or growth were not detected, and density-dependent effects were either weak or positive. While the positive effects of increased summer temperatures on juvenile condition may benefit overwintering survival, they cannot compensate for high pre-settlement mortality from warming winter–spring temperatures. We conclude the critical thermal bottleneck for juvenile abundance occurs pre-settlement.

Hoary Squash Bees (Eucera pruinosa: Hymenoptera: Apidae) Provide Abundant and Reliable Pollination Services to Cucurbita Crops in Ontario (Canada)

The increasing demand for insect-pollinated crops highlights the need for crop pollination paradigms that include all available pollinators. In North America, Cucurbita crops (pumpkin, squash) depend on both wild (solitary and Bombus spp.: Hymenoptera: Apidae) and managed honey bees (Apis mellifera L. 1758: Hymenoptera: Apidae) for pollination. Temporal and spatial differences in abundance may determine which bee taxa are the most important pollinators of Cucurbita crops. We surveyed bees visiting Cucurbita crop flowers on 19 farms over four years (2015-2018) during the crop flowering period (July 1-August 30 from 06:00-12:00). All the farms surveyed had hoary squash bees (Eucera pruinosa (Say, 1867), and most also had some combination of honey bees, bumble bees (Bombus spp.), or other wild bees present on their Cucurbita crop flowers. All four bee taxa were present on about two-thirds of farms. Spatially and temporally, wild bees were more abundant on Cucurbita crop flowers than managed honey bees. Hoary squash bees were the most abundant wild bees, maintaining their abundance relative to other wild bee taxa year-over-year. Male hoary squash bees were both more frequently and consistently seen visiting crop flowers than females in all years. Peak activity of hoary squash bees and bumble bees coincided with the daily crop pollination window, whereas peak activity of honey bees and other wild bees occurred after that window. In addition to elucidating the ecological interactions among wild and managed pollinators on Cucurbita crops, our work provides a novel practical way to evaluate pollinator abundance using a crop-centered benchmark framework.

Spatial and seasonal comparisons of growth of wild and stocked juvenile lake trout in Lake Champlain

After 42 years of stocking in Lake Champlain, recruitment of wild juvenile lake trout (Salvelinus namaycush) was first observed in 2015. Abundance of wild lake trout juveniles was spatially heterogeneous. Recruitment of wild fish to age-1 and subsequent survival are likely related to growth including overwinter growth. We hypothesized that growth potential or growth-related mortality of wild and stocked fish may explain spatial differences in abundance. We collected juvenile (age-0 to 3) lake trout by bottom trawling in the central, north, and south Main Lake every 2–4 weeks during the ice-free season, 2015–2018. The percentage of wild juveniles increased from 27.8% of the total catch in 2015 to 65.7% in 2018. Rates of growth in length and change in condition were compared in wild versus stocked lake trout, among sampling areas, and between seasons (sampling season relative to winter). Wild juveniles grew equally or faster in length than stocked juveniles at the same age, but changed more slowly in condition. There was a higher percentage of wild juveniles in the central sampling area than the north and south, but no differences in growth among sampling areas. Wild and stocked fish grew in length over winter, but most cohorts (6 of 7) maintained or increased condition. Results indicate high growth potential of wild juvenile lake trout and progress toward population restoration.

Spatiotemporal changes in juvenile lake sturgeon abundance in a large river

Monitoring trends in a long-lived species such as lake sturgeon (Acipenser fulvescens) has it challenges. Targeting the correct life stage to monitor can provide different and contrasting results. Early life stages experience high variable mortality and are often not a good predictor of population trend. Juvenile lake sturgeon (i.e., 5–10 years) experience high survival and could be a good life stage to monitor for assessing population trends. A structured, randomized gillnetting program, Broad-scale Monitoring, which was selective to juvenile lake sturgeon, was conducted over three cycles (i.e., 5 + years apart) in three contiguous Ottawa River reaches supporting lake sturgeon. In this study, we assessed spatiotemporal changes in juvenile lake sturgeon abundance among cycles, among and within the three river reaches. Density rasters based on catch records of lake sturgeon spatially were created using multilevel B-splines. Spatial differences in abundance among cycles was determined by obtaining the difference between the rasters. Three cycles of Broad-scale Monitoring sampled 334 lake sturgeon at a mean CPUE of 0.90 (0.12 SE) sturgeon • gang−1 and a mean total length 673 mm (115 SD) from all three reaches. The relative abundance of juvenile lake sturgeon did not significantly vary among sample cycles, however, CPUE varied within reaches among cycles. There was a spatiotemporal change in density with a decrease in the lowest reach whereas juvenile lake sturgeon density increased the most in the upper reach. The approach used in this study has the potential to monitor spatiotemporal changes in juvenile lake sturgeon abundance populations and may prove effective when assessing rehabilitation or fisheries management efforts.

Пространственная вариабельность и пищевые характеристики популяций желетелых в акватории Крыма в летний период

Численность, биомасса, размерная структура популяций желетелых хищников [медуза Aurelia aurita Linnaeus, 1758; гребневики Mnemiopsis leidyi A. Agassiz, 1865 и Pleurobrachia pileus (O. F. Müller, 1776)] и интенсивность питания двух видов (A. aurita и M. leidyi) исследованы в раннелетний период (июнь) 2016 г. на 45 станциях, охватывавших зону шельфа у берегов Крыма от м. Тарханкут до г. Керчи, а также на 3 станциях глубоководного района с координатами 44°23′N–45°5′N и 32°22′E–36°36′E. Сбор материала проводили вертикальными тралениями от дна (10–100 м) до поверхности на шельфовых станциях и от глубины с σt = 16,2 до поверхности ― на глубоководных, используя модифицированную сеть Богорова ― Расса с диаметром входного отверстия 80 см и ячеëй 500 мкм. Спектр питания определяли под микроскопом в лаборатории сразу после вылова животных, рассчитывая впоследствии суточные рационы и скорость выедания зоопланктона. Установлены пространственные различия в биомассе и численности отдельных видов: максимальная биомасса A. aurita, преобладавшей во всех районах, отмечена в Евпаторийско-Севастопольском районе и обусловлена большими скоплениями среднеразмерных особей новой генерации. Гребневик P. pileus доминировал по численности в районе халистазы. Пищевой спектр медуз был очень разнообразен и включал различные стадии Copepoda, Tunicata, Cladocera, а также меропланктонные организмы ― велигеров Bivalvia и Gastropoda. Халистатическая зона с большими глубинами характеризовалась максимальным количеством видов планктонных Copepoda в пище A. aurita. Среднесуточные рационы медуз, рассчитанные по содержанию пищи в гастральной полости и по времени переваривания, изменялись в широких пределах от района к району. Самыми низкими показатели были в Каркинитском заливе [(0,113 ± 0,10) мг C·экз.-1·сут-1, или (1,6 ± 2,18) % C тела], где большую долю пищи составляли водоросли Coscinodiscus granii Gough, 1905. Наиболее интенсивно питались животные в халистатической области [(0,687 ± 0,094) мг C·экз.-1·сут-1, или (56,2 ± 23,7) % C тела], в пище преобладали Calanus euxinus Hulsemann, 1991 и Pseudocalanus elongatus Boeck, 1865. Ни в одном из районов A. aurita не могла компенсировать затраты на дыхание за счёт потребления мезозоопланктона. Наибольший пресс на зоопланктон оказывала популяция медуз в Каркинитском заливе и в Евпаторийско-Севастопольском районе, хотя во всех исследованных районах её пресс был очень низок и не приводил к кардинальному сокращению численности зоопланктонного сообщества.

Effects of distance on detectability of Arctic waterfowl using double-observer sampling during helicopter surveys.

Aerial survey is an important, widely employed approach for estimating free‐ranging wildlife over large or inaccessible study areas. We studied how a distance covariate influenced probability of double‐observer detections for birds counted during a helicopter survey in Canada’s central Arctic. Two observers, one behind the other but visually obscured from each other, counted birds in an incompletely shared field of view to a distance of 200 m. Each observer assigned detections to one of five 40‐m distance bins, guided by semi‐transparent marks on aircraft windows. Detections were recorded with distance bin, taxonomic group, wing‐flapping behavior, and group size. We compared two general model‐based estimation approaches pertinent to sampling wildlife under such situations. One was based on double‐observer methods without distance information, that provide sampling analogous to that required for mark–recapture (MR) estimation of detection probability, p^, and group abundance, G^, along a fixed‐width strip transect. The other method incorporated double‐observer MR with a categorical distance covariate (MRD). A priori, we were concerned that estimators from MR models were compromised by heterogeneity in p^ due to un‐modeled distance information; that is, more distant birds are less likely to be detected by both observers, with the predicted effect that p^ would be biased high, and G^ biased low. We found that, despite increased complexity, MRD models (ΔAICc range: 0–16) fit data far better than MR models (ΔAICc range: 204–258). However, contrary to expectation, the more naïve MR estimators of p^ were biased low in all cases, but only by 2%–5% in most cases. We suspect that this apparently anomalous finding was the result of specific limitations to, and trade‐offs in, visibility by observers on the survey platform used. While MR models provided acceptable point estimates of group abundance, their far higher stranded errors (0%–40%) compared to MRD estimates would compromise ability to detect temporal or spatial differences in abundance. Given improved precision of MRD models relative to MR models, and the possibility of bias when using MR methods from other survey platforms, we recommend avian ecologists use MRD protocols and estimation procedures when surveying Arctic bird populations.

Persistent differences between coastal and offshore kelp forest communities in a warming Gulf of Maine.

Kelp forests provide important ecosystem services, yet coastal kelp communities are increasingly altered by anthropogenic impacts. Kelp forests in remote, offshore locations may provide an informative contrast due to reduced impacts from local stressors. We tested the hypothesis that shallow kelp assemblages (12–15 m depth) and associated fish and benthic communities in the coastal southwest Gulf of Maine (GOM) differed significantly from sites on Cashes Ledge, 145 km offshore by sampling five coastal and three offshore sites at 43.0 +/- 0.07° N latitude. Offshore sites on Cashes Ledge supported the greatest density (47.8 plants m2) and standing crop biomass (5.5 kg m2 fresh weight) of the foundation species Saccharina latissima kelp at this depth in the Western North Atlantic. Offshore densities of S. latissima were over 150 times greater than at coastal sites, with similar but lower magnitude trends for congeneric S. digitata. Despite these differences, S. latissima underwent a significant 36.2% decrease between 1987 and 2015 on Cashes Ledge, concurrent with a rapid warming of the GOM and invasion by the kelp-encrusting bryozoan Membranipora membranacea. In contrast to kelp, the invasive red alga Dasysiphonia japonica was significantly more abundant at coastal sites, suggesting light or dispersal limitation offshore. Spatial differences in fish abundance mirrored those of kelp, as the average biomass of all fish on Cashes Ledge was 305 times greater than at the coastal sites. Remote video censuses of cod (Gadus morhua), cunner (Tautaogolabrus adspersus), and pollock (Pollachius virens) corroborated these findings. Understory benthic communities also differed between regions, with greater abundance of sessile invertebrates offshore. Populations of kelp-consuming sea urchins Stronglyocentrotus droebachiensis, were virtually absent from Cashes Ledge while small urchins were abundant onshore, suggesting recruitment limitation offshore. Despite widespread warming of the GOM since 1987, extraordinary spatial differences in the abundance of primary producers (kelp), consumers (cod) and benthic communities between coastal and offshore sites have persisted. The shallow kelp forest communities offshore on Cashes Ledge represent an oasis of unusually high kelp and fish abundance in the region, and as such, comprise a persistent abundance hotspot that is functionally significant for sustained biological productivity of offshore regions of the Gulf of Maine.

Spatial and seasonal changes in species diversity of epilithic fungi along environmental gradients of a river

Summary Fungi in stream ecosystems play a critical role in decomposing organic matter. However, despite their ecological importance, few studies have investigated spatial and seasonal variation in lotic fungi. We hypothesised that the taxonomic composition and richness of epilithic fungal assemblages would change along the longitudinal river gradient from headwaters to lower reaches. To test this hypothesis, we examined composition and richness in the Natori River, Japan, using PCR‐DGGE (polymerase chain reaction–denaturing gradient gel electrophoresis). We focused on five phyla of fungi or fungus‐like organisms (Ascomycota, Basidiomycota, Chytridiomycota, Zygomycota and Oomycota) that colonised cobbles to examine effects of dissolved organic matter and nutrients on fungal assemblages. We found that taxonomic richness on cobbles was as high as that on leaf litter and woody debris, suggesting that fungi can grow directly using dissolved organic matter and nutrients in the water, or indirectly via epilithic biofilms. Supporting the hypothesis, taxonomic richness increased longitudinally along the river in autumn, although the within‐site variation in composition on different cobbles was higher in the upper reaches. No spatial differences were detected in spring when spatial heterogeneity in water temperature was low. With the exception of Basidiomycota, nestedness in taxonomic composition was not detected in either spring or autumn, indicating that fungal taxa in the upper reaches are generally replaced by others downstream. These results suggest that taxonomic composition and richness of epilithic fungal assemblages change along the longitudinal gradient of the river, depending on water temperature and spatial differences in abundance and composition of dissolved organic matter and nutrients.

Annual variation in Calanus sinicus abundance and population structure in the northern boundary area of the Yellow Sea Cold Water Mass

The Yellow Sea Cold Water Mass (YSCWM) was suggested as an over-summering site of the dominant copepod species Calanus sinicus in coastal Chinese seas. Population abundance and structure were investigated by monthly sampling along three transects across the northern boundary of the YSCWM during 2009-2010. Results show that thermal stratification existed from June to October and that the vertical thermal difference increased with depth. Generally, total abundance was lowest in October and highest in June, and the female/male sex ratio was highest in February and lowest in August. Evident spatial differences in abundance were observed during the existence of the YSCWM. In June, total abundance averaged 158.8 ind/m(3) at well-stratified stations, and 532.1 ind/m(3) at other stations. Similarly, high abundances of 322.0 and 324.4 ind/m(3) were recorded from July to August inside the YSCWM, while the abundance decreased from 50.4 to 1.9 ind/m(3) outside the water mass. C. sinicus distribution tended to even out over the study area in September when the YSCWM disappeared. We believe that the YSCWM may retard population recruitment in spring and preserve abundant cohorts in summer. The summer population was transported to neritic waters in autumn. In addition to low temperatures, stable vertical structure was also an essential condition for preservation of the summer population. C. sinicus can survive the summer in marginal areas in high abundance, but the population structure is completely different in terms of C5 proportion and sex ratio.

Designing a benthic monitoring programme with multiple conflicting objectives

Summary1. Sound conservation and management advice usually requires spatial data on animal and plant abundances. The expense of programmes to determine species distributions and estimates of population sizes often limits sample size. To maximise effectiveness at minimal costs, optimisations of such monitoring efforts are critical. A monitoring programme can have multiple objectives with demands on the optimal sampling design that are often in conflict. Here, we develop an optimal sampling design for monitoring programmes with conflicting objectives, building on an existing intertidal benthic monitoring programme in the Dutch Wadden Sea and simulation models bounded in their parameter spaces by these data.2. We distinguish three possible objectives: (1) estimation of temporal changes and spatial differences in abundance and (2) mapping, that is, prediction of abundances at unsampled locations. Mapping abundances requires model‐based analyses using autocorrelation models. Such analyses are as good as the model fits the data; therefore, the final objective was (3) accurately estimating model autocorrelation parameters. To compare sampling designs, we used the following criteria: (1) minimum detectable difference in mean between two time periods or two areas, (2) mean prediction error and (3) estimation bias of autocorrelation parameters.3. Using Monte Carlo simulations, we compared five sampling designs with respect to these criteria (i.e. simple random, grid, two types of transects, and grid with random replacements) at four levels of naturally occurring spatial autocorrelation.4. The ideal sampling design for objectives (1) and (2) was grid sampling and for objective (3) random sampling. The sampling design that catered best for all three objectives combined was grid sampling with a number of random samples placed on gridlines.5. Grid sampling with a number of random samples is considered an accurate and powerful tool with the highest effectiveness. This sampling design is widely applicable and allows for accurate estimates of population sizes, monitoring of population trends, comparisons of populations/trends between years or areas, modelling autocorrelation, mapping species distributions and a mechanistic understanding of species distribution processes.

A Multi-Taxa Biological Survey of Passage Creek, Virginia

Identifying and conserving functioning headwater ecosystems is essential for ensuring the structure and function of natural ecosystem processes. The Passage Creek watershed (PCW) in Virginia is an upland tributary system of the North Fork Shenandoah River, which is found within the Potomac River basin. The PCW appears to maintain an array of terrestrial and fluvial habitats now uncommon in many adjacent watersheds because of human disturbance. We assessed the biotic condition of the PCW by sampling the fish, mollusk, and salamander assemblages throughout the watershed. We observed 29 fish, 9 salamander, and 4 aquatic mollusk species representing a variety of life histories and functional groups. Furthermore, we found that due to spatial differences in abundance and species richness, each assemblage offered unique insight into the condition of the PCW. The fish assemblage was indicative of those found in least disturbed areas within the Potomac basin, while salamander abundance and richness indicated areas of habitat degradation. Though we observed only one mussel species, the presence of native mussels suggested the PCW has maintained sufficient ecological condition to support long-lived animals potentially sensitive to low-level, additive, and compounding long-term disturbances, while neighboring watershed assemblages have collapsed. Given the relatively high species richness found within PCW, this watershed may be pivotal to the overall persistence of aquatic species in the Potomac basin and should receive high priority for future conservation efforts.

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m−2. The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.

Population Structure, Growth, and Production of the Wedge ClamDonax hanleyanus(Bivalvia: Donacidae) from Northern Argentinean Beaches

Donax hanleyanus Philippi, 1847 (Bivalvia: Donacidae) dominates fine to coarse sandy beach communities of the northern Argentinean Atlantic coast. The population biology of this intertidal wedge clam was studied by determining population structure, growth and production at the three locations Santa Teresita, Mar de las Pampas (both from December 2005 to December 2006) and Faro Querandí (from March 2005 to December 2006). Von Bertalanffy growth functions were established from length-frequency distributions using an asymptotic length (L∞) of 44 mm and the growth constants (K) of 0.46 and 0.47 y-1 respectively of Mar de las Pampas and Faro querandí. Compared with growth studies four decades ago, D. hanleyanus today is growing more slowly, but is reaching a higher maximum length. Longevity is estimated to be approximately five years. The present study confirms that the overall growth performance index is habitat-specific, grouping Donacidae into tropical/subtropical, temperate and upwelling species. The intertidal biomass of D. hanleyanus ranged between 0.04 and 1.32 g ash-free dry mass (AFDM) m-2yr-1. Individual production revealed the highest value at 30 mm length (0.16 g AFDM m-2yr-1) and annual production ranged between 0.08 and 0.99 g AFDM m-2yr-1, resulting in renewal rate values (P/) between 0.82 and 2.16. The P/ ratios of D. hanleyanus populations increased with decreasing latitude from temperate to tropical regions. Only at Santa Teresita D. hanleyanus was found living with the sympatric yellow clam Mesodesma mactroides. A significant negative correlation between abundances of both surf clams suggests that abundance peaks of D. hanleyanus are related with population crashes of M. mactroides. Spatial differences in abundance are significantly related to sand texture as confirmed by nonmetrical multidimensional scaling, but not to sea surface temperature. However, the decrease of D. hanleyanus seems to be principally related to human activities.

Distribution, abundance and life history of Mysis relicta ( Lovén) in the Feldberg Lake District, Germany

Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m −2, respectively. Highest abundance of adults was 110.4 ± 76.5 m −2 in summer, lowest abundances of 2.0 ± 4.0 m −2 occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m −2 was detected in summer and lowest of 0.8 ± 1.8 m −2 in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m −2 in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m −2 in Lake Zansen. There were great spatial differences in abundance in both lakes.

The Use of Mist-Net Capture Rates to Monitor Annual Variation in Abundance: A Validation Study

Constant-effort mist-netting has become an increasingly popular tool in long-term monitoring of bird populations. Monitoring programs often assume that variation in the capture rates of adults reflects variation in breeding densities of the sampled population. We test this assumption by comparing annual variation in mist-net capture rates to known variation in breeding densities of four species breeding in coastal scrub habitat at Point Reyes National Seashore, California. For the period 1980 to 1992, breeding densities for each species were assessed using spot-mapping observations of color-banded individuals. These were compared to capture rates calculated from constant-effort mist-netting. Capture rates of adults correlated significantly with breeding density for Spotted Towhees (Pipilo maculatus), Song Sparrows (Melospiza melodia), and Wrentits (Chamaea fasciata), but not for White-crowned Sparrows (Zonotrichia leucophrys). Analysis of covariance confirmed that the relationship of mist-net capture rates to breeding density differed among species. Independent of the effects of breeding density on capture rates, adult capture rates of the four species were higher in years with high rainfall. Among Wrentits and Song Sparrows, approximately 50% or more of adults caught were not occupying territories at the study site; the same bias may exist among other species as well. We conclude that relative changes in breeding density over time can be inferred from variation in mist-net capture rates for some, but not all, species. Additional studies are needed to validate the use of mist nets to assess spatial differences in abundance and to monitor temporal changes in abundance in habitats other than coastal scrub.

Do spatial differences in the abundance of two serranid fishes in estuaries of tropical Australia reflect long-term salinity patterns?

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 137:39-49 (1996) - doi:10.3354/meps137039 Do spatial differences in the abundance of two serranid fishes in estuaries of tropical Australia reflect long-term salinity patterns? Sheaves M Epinephelus coioides and E. malabaricus are closely related species of serranid fishes. They are similar in appearance, occupy the same habitats and are represented in estuaries of northeastern tropical Australia almost entirely by juveniles. Fish traps were used to sample these 2 species from 3 estuaries on the northeast coast of tropical Australia over a 2 yr period. Patterns of distribution, abundance and size structure were compared. Despite the similarities between the 2 species, they showed quite different patterns of distribution and abundance, both within and between estuaries. In seaward parts of the estuaries the numbers of E. coioides were similar to or greater than those of E. malabaricus. However, in upstream areas E. malabaricus became much more abundant than E. coioides. The reasons for this change in dominance are unknown. However, upstream areas of the estuaries exhibited extreme levels of salinity (either hypersaline or hyposaline) and catches of the 2 species correlated with the maximum deviation in salinity. This suggests that if salinity, or some correlated variable, does influence the abundance of the 2 species, it is through long-term effects rather than short-term changes. Regardless of the reason, these spatial differences in abundance suggest that E. malabaricus is better equipped to deal with the challenges of estuary life than is E. coioides. Estuary . Tropical . Fish distribution . Salinity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 137. Publication date: June 27, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Population Ecology of the Biennials Cirsium Vulgare and Cynoglossum Officinale in a Coastal Sand-Dune Area

(1) Demographic data were collected on the biennials Cirsium vulgare and Cynoglossum officinale in a coastal sand-dune area in the Netherlands. Over ninety local populations were observed in 2 m x 2 m plots for a three-year period (1981-84). (2) Within two years Cirsium vulgare disappeared from 51% of the plots, while Cynoglossum officinale disappeared from only 7% of the plots. Reduction of the total dune population during the study period was evident for both species; the number of seedlings that established was insufficient to compensate for the losses from the population because of death of rosettes and flowering plants. (3) Large temporal and spatial variation existed in reproductive success, measured as the number of surviving seedlings per reproductive individual. Seedling survival in the two species was lowest in the dry summer of 1983 and in exposed vegetation. As a result of the low establishment in open habitats the main distribution shifted from exposed habitats to plots in the direct vicinity of shrubs and trees. This shift was most obvious in Cynoglossum officinale. (4) Using a modified key factor analysis, plots with high early mortality also showed high total mortality during the life of the 1981 cohort: events early in the life of individuals determine the spatial differences in abundance of the adults. These events include failure to produce viable seeds, seed predation and early seedling mortality in Cirsium vulgare, and failure to produce viable seeds, failure to germinate and early seedling mortality in Cynoglossum officinale. (5) The reduction of the population appeared not to be due to systematic processes such as the accumulation of litter or the increase of perennial vegetation. Stochastic factors such as rainfall and seed predation had most influence on population recruitment. (6) Dispersal, delayed germination and delay of flowering permit a monocarpic organism to bridge years or sites with failing reproduction. In these two species the importance of a persistent seedbank in the soil is limited. The dispersal rate between populations in different vegetation types was probably low. Delayed flowering was most pronounced in Cynoglossum officinale. The proportion of the rosettes of one year and older delaying reproduction varied between 75% and 95%. In Cirsium vulgare this figure varied between 53% and 80%. The large proportion of rosettes that delayed reproduction buffered the population against low seedling recruitment in some years.

Temporal and Spatial Patterns of Abundance of the Chydoridae (Cladocera) in Lake Itasca, Minnesota

The chydorid populations of Lake Itasca, Minnesota, were monitored over a 2.5—yr period by pattern sampling. Of the 24 species collected, 15 were sufficiently abundant to allow analysis of population trends. Chydorid species have two basic patterns of abundance. One group of species exhibits only a summer density peak. The second group shows one abundance peak in summer and a second peak in fall or winter. All species experience a precipitous decline in density following the summer peak. Population growth in chydorids is limited by different factors during different times of the year. During periods of ice cover most species are apparently limited by a reduction in primary productivity due to reduced light penetration rather than by water temperature. Spring chydorid populations are limited by temperature. Summer populations, at least for abundant species, are limited by predation. Chydorid species are distributed patchily within Chara beds. Patchiness is moderate in spring, declines to low levels during summer, and peaks in the fall for most species. Patchiness remained about constant during the summer decline in density. Experimentation showed that heterogeneity of the physical habitat is not a necessary cause of patchiness. A Bray—Curtis—type ordination was performed on data from a complete year of monitoring. The primary component of variation extracted from the data matrix is due to temporal differences in abundance among species. The second major source of variation is due to spatial differences in abundance (habitat preference). The most abundant chydorid species tent to have similar habitats and temporal patterns of abundance.