Areas Of Low Abundance Research Articles

Optimal methods for identification of dominants for submerged aquatic vegetation on a case of the northwestern Tatar Strait

Dominant species are identified at infracenotic level for aquatic vegetation in the sublittoral zone of the northwestern Tatar Strait (Japan Sea) on the data collected in 2010–2019. Seven different methods of the identifying are considered based both on visual qualitative and quantitative assessments and on instrumental estimations of abundance for 44 macrophyte species. Depending on applied method, 19–25 species (7–22 % of total number of species) are identified as the dominants, including 10 species identified by all methods. List of these 10 species is defined as the core of vegetation that determines its general properties and the species are determined as unconditional dominants, in opposite to other ones identified by at least one method — conditional dominants. All macrophyte species in areas of low abundance do not meet the dominance criteria. All lists of dominants, including those based on visual estimates of projective cover and its physiognomy, are statistically indistinguishable (p = 0.55–0.92, by pairs of lists) and highly similar (Bray-Curtis index 0.80–0.95, Jacquard index 0.65–0.87), with one exception for the list identified by the method of ranking for the average projective cover (indices of similarity with other lists: 0.68–0.71 by Bray-Curtis, 0.46–0.56 by Jacquard). This visual method of projective cover assessment is combined with the procedure of species dividing to dominant and non-dominant groups. Quantitative criteria of projective cover and biomass, by species (thresholds 0.2 and 1.0 kg/m3, respectively) are used for dividing on cenotic and landscape levels and ranking with Brotskaya-Zenkevich index and its modification for projective cover is used for dividing on regional level. Visual methods are available for verification, but the lists of dominants based on visual and instrumental assessments should be mutually verified.

Eco-evolutionary rescue promotes host-pathogen coexistence.

Emerging infectious pathogens are responsible for some of the most severe host mass mortality events in wild populations. Yet, effective pathogen control strategies are notoriously difficult to identify, in part because quantifying and forecasting pathogen spread and disease dynamics is challenging. Following an outbreak, hosts must cope with the presence of the pathogen, leading to host-pathogen coexistence or extirpation. Despite decades of research, little is known about host-pathogen coexistence post-outbreak when low host abundances and cryptic species make these interactions difficult to study. Using a novel disease-structured N-mixture model, we evaluate empirical support for three host-pathogen coexistence hypotheses (source-sink, eco-evolutionary rescue, and spatial variation in pathogen transmission) in a Neotropical amphibian community decimated by Batrachochytrium dendrobatidis (Bd) in 2004. During 2010-2014, we surveyed amphibians in Parque Nacional G. D. Omar Torríjos Herrera, Coclé Province, El Copé, Panama. We found that the primary driver of host-pathogen coexistence was eco-evolutionary rescue, as evidenced by similar amphibian survival and recruitment rates between infected and uninfected hosts. Average apparent monthly survival rates of uninfected and infected hosts were both close to 96%, and the expected number of uninfected and infected hosts recruited (via immigration/reproduction) was less than one host per disease state per 20-m site. The secondary driver of host-pathogen coexistence was spatial variation in pathogen transmission as we found that transmission was highest in areas of low abundance but there was no support for the source-sink hypothesis. Our results indicate that changes in the host community (i.e., through genetic or species composition) can reduce the impacts of emerging infectious disease post-outbreak. Our disease-structured N-mixture model represents a valuable advancement for conservation managers trying to understand underlying host-pathogen interactions and provides new opportunities to study disease dynamics in remnant host populations decimated by virulent pathogens.

Traditional knowledge and cultural importance of Borassus aethiopum Mart. in Benin: interacting effects of socio-demographic attributes and multi-scale abundance

BackgroundEliciting factors affecting distribution of traditional knowledge (TK) and cultural importance of plant resources is central in ethnobiology. Socio-demographic attributes and ecological apparency hypothesis (EAH) have been widely documented as drivers of TK distribution, but their synergistic effect is poorly documented. Here, we focused on Borassus aethiopum, a socio-economic important agroforestry palm in Africa, analyzing relationships between the number of use-reports and cultural importance on one hand, and informant socio-demographic attributes (age category and gender) on the other hand, considering the EAH at multi-scale contexts. Our hypothesis is that effects of socio-demographic attributes on use-reports and cultural importance are shaped by both local (village level) and regional (chorological region level) apparency of study species. We expected so because distribution of knowledge on a resource in a community correlates to the versatility in the resource utilization but also connections among communities within a region.MethodsNine hundred ninety-two face-to-face individual semi-structured interviews were conducted in six villages of low versus high local abundance of B. aethiopum spanning three chorological regions (humid, sub-humid and semi-arid) also underlying a gradient of increasing distribution and abundance of B. aethiopum. Number of use-reports and score of importance of uses of B. aethiopum were recorded in six use-categories including medicine, food, handcraft, construction, firewood, and ceremonies and rituals. Data were analyzed using Poisson and ordered logistic models.ResultsInformants listed 121 uses for B. aethiopum: medicine (66 uses), handcraft (16 uses), food (16 uses), construction (12 uses), firewood (6 uses), and ceremonies and rituals (5 uses); but food use was the most culturally important use (2.45 ± 0.03), followed by construction (0.61 ± 0.03), medicinal (0.57 ± 0.03) and handcraft (0.56 ± 0.03), firewood (0.29 ± 0.02), and ceremonies and rituals (0.03 ± 0.01). Food use was the most important for women who were specialized in hypocotyls and fruits collection for commercialization. Men valued more the species for handcrafting, construction, and medicine. The number of use-reports was significantly dependent on age category and gender, and differences between age categories (young, adult, and old) in particular were dependent upon local and regional apparency. In particular, discrepancies among age categories were higher in areas of low abundance and distribution, which may be linked to different speed in the process of knowledge acquisition. In areas of low abundance, the species past abundance was also found instrumental in understanding current knowledge distribution.ConclusionFindings suggest that studies aiming at understanding relationship between current TK and cultural importance of a resource on one hand and socio-demographic attributes on the other hand should consider the resource current local and regional apparency but further its local past abundance. The study also confirms that B. aethiopum is a socio-economic important species in Benin.

Causes and consequences of spatial variation in sex ratios in a declining bird species.

Summary Male‐biased sex ratios occur in many bird species, particularly in those with small or declining populations, but the causes of these skews and their consequences for local population demography are rarely known. Within‐species variation in sex ratios can help to identify the demographic and behavioural processes associated with such biases.Small populations may be more likely to have skewed sex ratios if sex differences in survival, recruitment or dispersal vary with local abundance. Analyses of species with highly variable local abundances can help to identify these mechanisms and the implications for spatial variation in demography. Many migratory bird species are currently undergoing rapid and severe declines in abundance in parts of their breeding ranges and thus have sufficient spatial variation in abundance to explore the extent of sex ratio biases, their causes and implications.Using national‐scale bird ringing data for one such species (willow warbler, Phylloscopus trochilus), we show that sex ratios vary greatly across Britain and that male‐biased sites are more frequent in areas of low abundance, which are now widespread across much of south and east England. These sex ratio biases are sufficient to impact local productivity, as the relative number of juveniles caught at survey sites declines significantly with increasing sex ratio skew.Sex differences in survival could influence this sex ratio variation, but we find little evidence for sex differences in survival increasing with sex ratio skew. In addition, sex ratios have become male‐biased over the last two decades, but there are no such trends in adult survival rates for males or females. This suggests that lower female recruitment into low abundance sites is contributing to these skews.These findings suggest that male‐biased sex ratios in small and declining populations can arise through local‐scale sex differences in survival and dispersal, with females recruiting disproportionately into larger populations. Given the high level of spatial variation in population declines and abundance of many migratory bird species across Europe at present, male‐biased small populations may be increasingly common. As singing males are the primary records used in surveys of these species, and as unpaired males often sing throughout the breeding season, local sex ratio biases could also be masking the true extent of these population declines.

The abundance structure of Azorella selago Hook. f. on sub-Antarctic Marion Island: testing the peak and tail hypothesis

Understanding the spatial distribution of organisms and the factors underlying it are key questions in ecology. Two competing hypotheses exist about the form of spatial variation in abundance. The abundant centre hypothesis suggests that abundance is highest in the centre of a species’ range and declines towards the range margins. By contrast, the peak and tail spatial pattern in abundance posits that several high abundance areas exist across a species range. Here, we test these competing hypotheses by surveying the abundance of the keystone plant species Azorella selago Hook. f. (Apiaceae) across sub-Antarctic Marion Island on a regular spatial grid. We also examine several factors that might explain variation in abundance. Azorella selago occurs between ca. 30 and 850 m above sea level, with sharp discontinuities in abundance at ca. 30 m and at 667 m a.s.l. The survey and analyses revealed a complex abundance structure with patches of high abundance alternating with areas of low abundance or absence, providing support for the peak and tail hypothesis, but with some support for the abundant centre idea too. Variation in abundance was best explained by a model including the negative effects of elevation and of closed vegetation. Our work provides support for the peak and tail pattern of spatial variation in abundance, which has profound importance for understanding the mechanisms underlying the spatial distribution of abundance and other macroecological regularities.

Lutzomyia longipalpis abundance in the city of Posadas, northeastern Argentina: variations at different spatial scales

The distribution of Lutzomyia longipalpis is heterogeneous with a pattern of high abundance areas (HAAs) embedded in a matrix of low abundance areas (LAAs). The objective of this study was to describe the variability in the abundance of Lu. longipalpis at two different spatial levels and to analyse the relationship between the abundance and multiple environmental variables. Of the environmental variables analysed in each household, the condition that best explained the differences in vector abundance between HAA-LAA was the variable "land_grass", with greater average values in the peridomestic environments within the LAA, and the variables "#sp tree", "#pots" and "dist_water" that were higher in the HAA. Of the environmental variables analysed in the patches, the variable "unpaved_streets" was higher in the LAAs and the variable "prop_inf_dogs" was higher in the HAAs. An understanding of the main environmental variables that influence the vector distribution could contribute to the development of strategies for the prevention and control of visceral leishmaniasis (VL). This is the first work in which environmental variables are analysed at the micro-scale in urban areas at the southern edge of the current range of Lu. longipalpis. Our results represent a significant contribution to the understanding of the abundance of the vector in the peridomestic habitats of the region.

Field optimisation of MosquiTRAP sampling for monitoring Aedes aegypti Linnaeus (Diptera: Culicidae)

A sticky trap designed to capture gravid Aedes (Stegomyia) aegypti mosquitoes, MosquiTRAP, has been evaluated for monitoring this species in Brazil. However, the effects of trap densities on the capture rate of Ae. aegypti females and the sensitivity of vector detection are still unknown. After a preliminary study has identified areas of high and low female mosquito abundance, a set of experiments was conducted in four neighbourhoods of Belo Horizonte (state of Minas Gerais, Brazil) using densities of 1, 2, 4, 8, 16, 32 and 64 traps per block. Trap sensitivity (positive MosquiTRAP index) increased significantly when 1-8 MosquiTRAPs were installed per block in both high and low abundance areas. A strong fit was obtained for the total number of mosquitoes captured with increasing trap densities through a non-linear function (Box-Lucas) (r² = 0,994), which likely exhibits saturation towards an equilibrium level. The capacity of the Mean Female Aedes Index to distinguish between areas of high and low Ae. aegypti abundance was also investigated; the achieved differentiation was shown to be dependent on the MosquiTRAP density.

Population Genetics and Dynamics of Spotted Seatrout in the Estuarine Waters of Texas

A geospatial database of spotted seatrout (Cynoscion nebulosus) abundance along the Texas shoreline was generated, using 33 years of intensive gill net sampling data by the Texas Parks and Wildlife Department. The resulting landscape demographic data was used to identify areas of low individual abundance, which were evaluated as putative subpopulation boundaries. Quantitative population genetic analysis was conducted using a recently published genetic data set of mitochondrial DNA haplotypes, and a new data set of nuclear microsatellites. A significant mtDNA AMOVA result was obtained when samples were pooled into northern, mid-coast and southern spatial partitions based upon geospatial data (Fct = 0.030, P = 0.003). This three-partition model captured more genetic divergence at the group level than any other model examined. Similarly, the three-partition model resulted in a small but significant group association in the microsatellite AMOVA (Fct = 0.003, P = 0.009). Multivariate cluster analyses of both data sets indicated that at least three distinctive subpopulations of spotted seatrout exist within Texas waters. The genetic data are consistent with previous studies that indicate the presence of distinctive subpopulations of spotted seatrout in Texas coastal waters, and with geospatial abundance data indicating areas of low abundance, between adjacent subpopulations along the northern and southern Texas coastline.

Distribution of axial lava domes along a superfast overlapping spreading center, 27–32°S on the East Pacific Rise

Deep‐towed DSL‐120 bathymetric data are used to investigate the pattern of lava dome formation along a superfast spreading portion of the southern East Pacific Rise (EPR), including the overlapping limbs of a giant (120 × 120 km) propagator near 29°S. Along the 670 km of the axis surveyed, 1172 small domes were identified using a closed contour algorithm. Their abundance, defined by spatial density, is well correlated with the along‐axis relief of the ridge crest. Where the western and eastern limbs plunge toward the overlap zone, densities are high (3–6 km−2); however, where the axial depth profile is shallow and flat, densities are comparably low (0.4 km−2). Volcanic domes within the low abundance areas are characterized by lower ratios of height to basal radius (0.15 versus 0.22), smaller maximum heights (18 versus 40 m), and a larger relative percentage of small versus large mounds. The zone of high dome abundance encompasses the overlapping limbs of the rift and extends more than 100 km to the north and south beyond the overlap zone. Domes form dominantly during low effusion rate, point‐source eruptions, which suggests that discontinuous melt lenses underlie the ridge axis proximal to the overlapper. Conversely, fissure‐fed sheet flows dominate along the more distal segments, implying the presence of a more continuous axial magma lens. Throughout the survey area, dome abundance increases systematically near second‐order segment boundaries. Within the high abundance zone, some third‐order offsets also correlate with increased dome production, but local peaks in abundance are not tied exclusively to higher‐order ridge offsets. Where dome abundance is low, domes are clustered tightly near second‐order offsets and there is no increase in dome abundance near third‐order segment boundaries.

A DELURY DEPLETION ESTIMATOR FOR WALLEYE POLLOCK (THERAGRA CHALCO-GRAMMA) IN THE EASTERN BERING SEA

. Concerns about local depletion of fish populations are intensifying, as interest becomes focused on finer spatial and temporal scales. We used the DeLury model to investigate local depletion of the eastern Bering Sea walleye pollock population by its fishery by using spatial and temporal scales thought to meet assumptions about closure and applicability. Local depletion is estimated as the slope of logarithmic catch-per-unit-effort (CPUE) from the fishery versus cumulative effort, with data from 1995 1999 stratified by small areas, short seasons and years. Of 237 depletion estimators, 172 had negative slopes, 94 of which were significant, a greater number than would be expected by chance alone. Of the 65 positive slopes, 19 were significantly positive, which is also more than would be expected. Cumulative depletion over a season was inversely related to estimated initial biomass, total catch, and total effort, indicating that depletion is detected more easily in areas of low abundance and consequently lower catch and effort. Our fine-scale estimates of depletion are much smaller than the overall depletion from annual stock assessments, showing that commercial data alone can be at best a relative index of depletion. This hyperstable relationship may result from the lack of search time in the measure of effort, fish finding technology and schooling behavior of pollock. Evidence also suggests that measures that were taken starting in 1999 to disperse the exploitation pressure in space and time may decrease local depletion, and that pollock may repopulate an exploited area in a relatively short time period (weeks).

Genetic structure of the cyclic fossorial water vole (Arvicola terrestris): landscape and demographic influences

Genetic structure can be strongly affected by landscape features and variation through time and space of demographic parameters such as population size and migration rate. The fossorial water vole (Arvicola terrestris) is a cyclic species characterized by large demographic fluctuations over short periods of time. The outbreaks do not occur everywhere at the same time but spread as a wave at a regional scale. This leads to a pattern of large areas (i.e. some hundreds of km2), each with different vole abundances, at any given time. Here, we describe the abundance and genetic structures in populations of the fossorial water vole. We use the data to try to understand how landscape and demographic features act to shape the genetic structure. The spatial variability of vole abundance was assessed from surface indices, collected in spring 2002 (April) in eastern central France. Genetic variability was analysed using eight microsatellite loci at 23 localities sampled between October 2001 and April 2002. We found some congruence between abundance and genetic structures. At a regional scale, the genetic disruptions were associated with both sharp relief and transition between an area of low abundance and another of high abundance. At a local scale, we observed a variation of the isolation-by-distance pattern according to the abundance level of vole populations. From these results we suggest that the dispersal pattern in cyclic rodent populations varies throughout the demographic cycle.

Modelling hunting strategies for the conservation of wild rabbit populations

Recently, European wild rabbit ( Oryctolagus cuniculus) populations have undergone a sharp decline that may be exacerbated by hunting. We investigate the effects of the timing of hunting on the conservation of wild rabbit using a model for rabbit population dynamics. Scenarios with different hunting rates and age strategies were simulated for different population qualities. We interviewed hunters to ascertain the degree to which they would accept a change in the timing of hunting. We also investigated the hunting pressure applied by hunters and its relationship with rabbit abundance. Modelling results indicate that the current hunting season has the greatest impact on rabbit abundance. Hunting in late spring optimises hunting extraction while conserving rabbit populations. When the rabbit population quality is low the effects of age strategies and the timing of hunting are less important than the effect of the hunting rate applied. Almost half the hunters would agree to policy changes. More than 75% of hunters implemented self-imposed hunting restrictions to improve rabbit populations, that were more frequently applied in high rabbit abundance areas. Therefore, changing the timing of hunting and increasing the participation of hunters in low abundance areas could optimise both the exploitation and the conservation of wild rabbit populations in southwestern Europe.

Translocation of Canada Geese branta canadensis in great Britain

In Britain, Canada Geese Branta canadensis have been translocated into new areas and/or areas of low abundance, principally in order to solve problems of local damage to crops or amenity grasslands and to provide new sport‐shooting opportunities for wildfowling clubs. This paper, based on a compilation of the available translocation records, provides the most definitive record of the extent of this activity, information necessary to understand the population history of Canada Geese in Britain. The details of 102 translocations, involving 1,910 birds, are collated and analysed. Capture and release information is considered, together with the subsequent fate of a proportion of the geese that had been relocated. The capture of Canada Geese for translocation was a ividespread activity in the 1950s/1960s, but there was particularly intense capture effort in some regions (eg central England) and at some sites (eg Clumber Park, Frampton, Melton Mowbray, Petworth) in Britain. The geese captured were ividely dispersed and there was considerable mixing of birds from different sub‐populations, residting in the introduction of Canada Geese into many new areas. The available evidence suggests that many geese remained in the areas in which they were released but others, of unknown age, sex or breeding status, returned to the areas from which they were taken; this was the case for 32% of recoveries with sufficient details.

Spatial Use and Group Dynamics of Sympatric Collared Peccaries and Feral Hogs in Southern Texas

Range and group dynamics of collared peccaries ( Tayassu tajacu ) and feral hogs ( Sus scrofa ) on the Welder Wildlife Refuge near Sinton, Texas, were studied during June 1991– November 1992. Eleven females (six peccaries, five hogs) representing distinct herds were outfitted with radiotransmitters. Crude densities of peccaries and hogs were estimated at 2.0 and 9.5 animals/km2, respectively. Peccary herds were highly cohesive units, in contrast to hogs, which exhibited a flexible grouping pattern. Ecological density of peccaries appeared to be negatively related to the density of observations of hogs within individual territories of peccaries. The distribution of group sizes also differed for peccaries in areas of low abundance of hogs (two herds) and in areas of high abundance of hogs (four herds). Size of home ranges did not differ between species. Home ranges of both species were larger during summer than spring. Overlap occurred between ranges of peccaries and hogs, but was diminished at the level of 75 and 50% core areas. Peccaries have declined on the study area for nearly 30 years, and feral hogs may have been involved in reducing herd and group size of peccaries.

Erratum

The fine- to coarse-scale distribution patterns of tuna larvae in the east Indian Ocean were investigated by a combination of continuous transect sampling using surface tows and random sampling using double oblique tows. Thunnus maccoyii was the most abundant species, reaching densities near patch centres of ∼22 m −3 in surface tows, which is 25 times greater than the highest previous records for tuna larvae. Patches of T maccoyii larvae in areas of high abundance appeared to be ∼5–15 km in diameter. Smaller patches in areas of low abundance were usually composed of older larvae Lloyd's index of patchiness was consistently high for all tuna species, ranging from 3.0 to 5.2 for T.maccoyii . There was no change in the index when tow distance was doubled to 1200 m, which suggests that the dominant patch size was somewhat larger than the larger sampling interval. Sampling larvae at the same site 4 days apart resulted in estimates of abundance that differed by an order of magnitude. Abundance estimated from a single station would depend largely on what day the station was occupied and where the sample was taken in relation to a patch.

Patterns of horizontal distribution of the larvae of southern bluefin (Thunnus maccoyii) and other tuna in the Indian Ocean

The abstract was incorrectly printed. The correct version is given below. Abstract. The fine- to coarse-scale distribution patterns of tuna larvae in the east Indian Ocean were investigated by a combination of continuous transect sampling usmg surface tows and random sampling using double oblique tows. Thunnus maccoyii was the most abundant species, reaching densities near patch centres of —22 m3 in surface tows, which is 25 times greater than the highest previous records for tuna larvae. Patches of T maccoyii larvae in areas of high abundance appeared to be —5—15 km in diameter. Smaller patches in areas of low abundance were usually composed of older larvae Lloyd's index of patchiness was consistently high for all tuna species, ranging from 3.0 to 5.2 for T.maccoyii. There was no change in the index when tow distance was doubled to 1200 m, which suggests that the dominant patch size was somewhat larger than the larger sampling interval. Sampling larvae at the same site 4 days apart resulted in estimates of abundance that differed by an order of magnitude. Abundance estimated from a single station would depend largely on what day the station was occupied and where the sample was taken in relation to a patch.