Estimates Of Relative Abundance Research Articles

Stock assessment of juvenile sturgeons in the Iranian water of the Caspian Sea by bottom trawl survey

The sturgeon stock assessment was performed to aim at estimation of absolute and relative abundance and determination of species composition at lower 10 m depths using the Si-Sara2 RV vessel in the Iranian coasts of the Caspian Sea in Guilan, Mazandaran and Golestan provinces during 6-30 September 2011-2012. In this study, 40 stations were selected on the basis of stratified random sampling design and then the stock estimation was performed using the swept area method. The study was carried out using bottom trawling with 9 m head rope. The time and speed of trawling in each station were 30 minutes and 2.5 knots respectively. The Catch per Unit of Effort (CPUE) in 2011–2012 were 7.03 and 6.96 individuals per trawling, respectively. The catch per unit of area in these years were found to be 1662 and 1644 fish in nm2, respectively. Total abundance of sturgeon juveniles was 13,327,164 individuals in 2011. So, the species composition included A. persicus (87.8%) and A. stellatus (12.2%). Total abundance of sturgeon juveniles was found to be 14,364,882 individuals in 2012 and the species composition comprised A. persicus (61.4%) and A. stellatus (38.6%). In 2011 the biomass of sturgeons in Iranian coastal water of the Caspian Sea was 295 tons and the composition of biomass included A. persicus (81.5%) and A. stellatus (18.5%), respectively. In the cruises conducted in 2011, this amount was estimated to be 217 tons comprising A. persicus (54.2%) and A. stellatus (45.8%), respectively. The results of this study in 2011–2012 showed remarkable abundance of juvenile sturgeons in Iranian coastal waters of the Caspian Sea in late summer and early autumn. So, by conserving these valuable stocks, the number of spawners will be increased in the future.

Opening the black box: an open‐source release of Maxent

This software note announces a new open‐source release of the Maxent software for modeling species distributions from occurrence records and environmental data, and describes a new R package for fitting such models. The new release (ver. 3.4.0) will be hosted online by the American Museum of Natural History, along with future versions. It contains small functional changes, most notably use of a complementary log‐log (cloglog) transform to produce an estimate of occurrence probability. The cloglog transform derives from the recently‐published interpretation of Maxent as an inhomogeneous Poisson process (IPP), giving it a stronger theoretical justification than the logistic transform which it replaces by default. In addition, the new R package, maxnet, fits Maxent models using the glmnet package for regularized generalized linear models. We discuss the implications of the IPP formulation in terms of model inputs and outputs, treating occurrence records as points rather than grid cells and interpreting the exponential Maxent model (raw output) as as an estimate of relative abundance. With these two open‐source developments, we invite others to freely use and contribute to the software.

Sampling, sequencing and the SAD

The Species Abundance Distribution (SAD) is a common metric for characterizing macroscopic ecological communities. Recently, this metric has been applied to analysis of microbial communities as well. However, as compared to macroscopic communities, sampling of microscopic communities is different. In particular, most microbial communities are studied using sequencing techniques. These techniques have known biases that result in certain taxa being detected more often than others, even if the taxa are present in the sample at equivalent abundances. There are, for example, amplification biases that result in some sequences being amplified more than others. Likewise, differences in genome size across organisms can result in different numbers of reads from different taxa, again resulting in biased detection. A number of bioinformatics methods have been devised to account for biases in sequencing data, allowing for more accurate estimates of relative taxon abundances. However, because the sampling process itself is affected by biased detection, and because sampling (and under-sampling in particular) can influence the shape of the SAD, it is possible that, even when corrected for through re-scaling, detection biases can affect SAD predictions from sequencing data. To test this hypothesis, we construct a simulation model of the sampling process, focusing on biased detection in shotgun sequencing that arises from genome size differences across microbial taxa. Interestingly, we find that, although genome size itself does not impact SAD predictions, predictions can vary depending on the range of genome sizes that are represented in a community, as well as how genome size is distributed (i.e., whether the majority of species have small versus large genomes). Our results suggest that care should be taken when comparing SADs across environments, particularly when those environments might have taxa with different genome size distributions. Furthermore, our results indicate that relatively deep sequencing might be required to avoid drawing spurious inferences about ecological differences across microbial communities.

Comparability of macroinvertebrate biomonitoring indices of river health derived from semi-quantitative and quantitative methodologies

Aquatic macroinvertebrates have been the basis for one of the primary indicators and a cornerstone of lotic biomonitoring for over 40 years. Despite the widespread use of lotic invertebrates in statutory biomonitoring networks, scientific research and citizen science projects, the sampling methodologies employed frequently vary between studies. Routine statutory biomonitoring has historically relied on semi-quantitative sampling methods (timed kick sampling), while much academic research has favoured fully quantitative methods (e.g. Surber sampling). There is an untested assumption that data derived using quantitative and semi-quantitative samples are not comparable for biomonitoring purposes. As a result, data derived from the same site, but using different sampling techniques, have typically not been analysed together or directly compared. Here, we test this assumption by comparing a range of biomonitoring metrics derived from data collected using timed semi-quantitative kick samples and quantitative Surber samples from the same sites simultaneously. In total, 39 pairs of samples from 7 rivers in the UK were compared for two seasons (spring and autumn). We found a strong positive correlation (rs=+0.84) between estimates of taxa richness based on ten Surber sub-samples and a single kick sample. The majority of biomonitoring metrics were comparable between techniques, although only fully quantitative sampling allows the density of the community (individual m−2) to be determined. However, this advantage needs to be balanced alongside the greater total sampling time and effort associated with the fully quantitative methodology used here. Kick samples did not provide a good estimate of relative abundance of a number of species/taxa and, therefore, the quantitative method has the potential to provide important additional information which may support the interpretation of the biological metrics.

Paleoecological quantitative analysis based on benthic foraminifera of the Aalenian–Bajocian boundary (upper Bradfordensis–lower Discites) in the Barranco de Agua Larga section (Betic Cordillera, Southern Spain)

To report, for the first time, the benthic foraminiferal assemblages recorded across the upper Bradfordensis–lower Discites ammonite zones (Aalenian–Bajocian boundary, Middle Jurassic) in the Barranco de Agua Larga section (Betic Cordillera, Southern Spain),in order to infer the paleecological conditions that affected their development. A total of 17 samples were collected in this reference section, and the composition of the foraminiferal assemblages recorded throughout the studied stratigraphical was analyzed using quantitative data obtained through the estimation of relative abundances and the calculation of several diversity indexes. The assemblages are abundant (a total of 3, 139 well-preserved specimens) and diverse(82 species). Their composition displays close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm (Type-A), Boreal Atlantic subdivision. The studied assemblages were developed in distal marine environmental conditions, at a depth situated above the level of the calcite compensation, well oxygenated and with normal salinity, although for certain times (Aalenian–Bajocian boundary) unfavorable environmental conditions could have developed. The sharp decrease in the abundance and diversity that was recorded during the Aalenian–Bajocian transition has also been recognized in other coeval basins of the Iberian Plate paleomargin, thus representing a bioevent of regional rank.

Effects of Tamarix removal on the community dynamics of riparian birds in a semiarid grassland

AbstractInvasion of riparian habitats by non‐native plants is a global problem that requires an understanding of community‐level responses by native plants and animals. In the Great Plains, resource managers have initiated efforts to control the eastward incursion of Tamarix as a non‐native bottomland plant (Tamarix ramosissima) along the Cimarron River in southwestern Kansas, United States. To understand how native avifauna interact with non‐native plants, we studied the effects of Tamarix removal on riparian bird communities. We compared avian site occupancy of three foraging guilds, abundance of four nesting guilds, and assessed community dynamics with dynamic, multiseason occupancy models across three replicated treatments. Community parameters were estimated for Tamarix‐dominated sites (untreated), Tamarix‐removal sites (treated), and reference sites with native cottonwood sites (Populus deltoides). Estimates of initial occupancy (ψ2006) for the ground‐to‐shrub foraging guild tended to be highest at Tamarix‐dominated sites, while initial occupancy of the upper‐canopy foraging and mid‐canopy foraging guilds were highest in the treated and reference sites, respectively. Estimates of relative abundance for four nesting guilds indicated that the reference habitat supported the highest relative abundance of birds overall, although the untreated habitat had higher abundance of shrub‐nesters than treated or reference habitats. Riparian sites where invasive Tamarix is dominant in the Great Plains can provide nesting habitat for some native bird species, with avian abundance and diversity that are comparable to remnant riparian sites with native vegetation. Moreover, presence of some native vegetation in Tamarix‐dominated and Tamarix‐removal sites may increase abundance of riparian birds such as cavity‐nesters. Overall, our study demonstrates that Tamarix may substitute for native flora in providing nesting habitat for riparian birds at the eastern edge of its North American range.

At the forefront: evidence of the applicability of using environmental DNA to quantify the abundance of fish populations in natural lentic waters with additional sampling considerations

Environmental DNA (eDNA) sampling has proven to be a valuable tool for detecting species in aquatic ecosystems. Within this rapidly evolving field, a promising application is the ability to obtain quantitative estimates of relative species abundance based on eDNA concentration rather than traditionally labor-intensive methods. We investigated the relationship between eDNA concentration and Arctic char (Salvelinus alpinus) abundance in five well-studied natural lakes; additionally, we examined the effects of different temporal (e.g., season) and spatial (e.g., depth) scales on eDNA concentration. Concentrations of eDNA were linearly correlated with char population estimates ([Formula: see text] = 0.78) and exponentially correlated with char densities ([Formula: see text] = 0.96 by area; 0.82 by volume). Across lakes, eDNA concentrations were greater and more homogeneous in the water column during mixis; however, when stratified, eDNA concentrations were greater in the hypolimnion. Overall, our findings demonstrate that eDNA techniques can produce effective estimates of relative fish abundance in natural lakes. These findings can guide future studies to improve and expand eDNA methods while informing research and management using rapid and minimally invasive sampling.

Comparison of Dog Surveys and Fall Covey Surveys in Estimating Fall Population Trends of Northern Bobwhite

The use of fall covey surveys to monitor population trends for northern bobwhite (Colinus virginianus; hereafter bobwhite) have been widely used in bobwhite research. Estimates of relative abundance from this monitoring technique are often important in assessing population responses to management practices or annual variation. However, conducting covey call surveys is labor intensive and typically can only be conducted during a narrow time frame. The use of dogs as a research tool may offer an efficient alternative to monitor bobwhite population trends. While dogs have been used in research for many other gallinaceous species, their application for bobwhite has received minimal research. To compare traditional and novel (dog) methods for both relative population abundance and density estimation, we conducted covey call surveys (50 points) and dog transects (32 km) during the fall (Sep-Oct) season from 2012-2014 at Beaver River WMA, Beaver County, Oklahoma, USA. A total of 306 detections were observed through fall covey count surveys, while only 44 detections were observed through dog transect surveys. Fall covey surveys yielded indices of 1.45, 2.04, and 3.21 detections per point count during 2012, 2013, and 2014, respectively. Dog transects yielded 0.23, 0.34, and 0.67 detections per km during 2012, 2013, and 2014, respectively. A Pearson’s correlation coefficient of 0.996 indicated high correlation between indices estimated between both survey methods. However, the low sample size for detections during dog surveys precluded any analysis that would yield bobwhite density estimates. Our results indicate that dog transects can be a method for estimating abundance indices for bobwhite. However, if estimates of bobwhite densities are of interest, then use of dog transect surveys are not recommended as only under high quail densities or with high observer efforts do enough detections accumulate for robust density estimation unless large effort is expended.

Red Snapper Distribution on Natural Habitats and Artificial Structures in the Northern Gulf of Mexico

AbstractIn 2011, an intensive, multiple‐gear, fishery‐independent survey was carried out in the northern Gulf of Mexico (GOM) to collect comprehensive age and length information on Red Snapper Lutjanus campechanus. Based on this synoptic survey, we produced a spatial map of Red Snapper relative abundance that integrates both gear selectivity effects and ontogenetically varying habitat usage. Our methodology generated a spatial map of Red Snapper at a 10‐km2 grid resolution that is consistent with existing knowledge of the species: Red Snapper occurred in relatively high abundances at depths of 50–90 m along the coasts of Texas and Louisiana and in smaller, patchy “hot spots” at a variety of depths along the Alabama coast and the west Florida shelf. Red Snapper biomass and fecundity estimates were higher for the northwestern GOM than for the northeastern GOM, as the latter area contained mostly smaller, younger individuals. The existence of similar surveys on petroleum platforms and artificial reefs also enabled us to calculate their relative contribution to Red Snapper distribution compared with that of natural habitats. We estimated that for the youngest age‐classes, catch rates were approximately 20 times higher on artificial structures than on natural reefs. Despite the high catch rates observed on artificial structures, they represent only a small fraction of the total area in the northern GOM; thus, we estimated that they held less than 14% of Red Snapper abundance. Because artificial structures—particularly petroleum platforms—attract mostly the youngest individuals, their contribution was even lower in terms of total population biomass (7.8%) or spawning potential (6.4%). Our estimates of Red Snapper relative abundance, biomass, and spawning potential can be used to design spatial management strategies or as inputs to spatial modeling techniques.

Summer Whistle Counts, Roadside Counts, and Fall Abundance of Northern Bobwhite

Reliable information on fall abundance of northern bobwhite (Colinus virginianus) is important for proper harvest management. Aerial surveys can provide reliable estimates of abundance, but can be expensive. Alternatively, whistle counts and roadside counts are indices of abundance that are relatively inexpensive, simple, and commonly used by biologists. We compared whistle and roadside counts conducted during summer to fall relative abundance (coveys/km) estimates obtained using helicopter surveys. All data were collected at the pasture scale (mean 1⁄4 1,716–2,762 ha) on the King Ranch (334,000 ha), which is comprised of 4 divisions across South Texas. Average survey effort was 245 km/year (1999–2001) and 1,194 km/year (1999–2007) for whistle and roadside counts, respectively, and 48 km/pasture/year (1999–2009) for fall helicopter surveys. Preliminary analyses demonstrate a moderate correlation between whistling bobwhite males and fall relative abundance (r 1⁄4 0.68). We collected age-based (i.e., chicks, juveniles, and adults) and population structure-based (i.e., singles, pairs, or coveys) data for roadside counts. Correlations between roadside counts and fall relative abundance varied by age and population structure. We found moderate correlation between total juveniles and fall relative abundance (r 1⁄4 0.49); all other correlations were low (r 1⁄4 ,0.36). We explore the feasibility of using summer whistle and roadside counts as a surrogate for fall relative abundance and discuss optimum timing to conduct surveys.

Species diversity of freshwater decapod crustaceans (crabs and shrimps) from Colombia

The aim of this paper is to characterize the species diversity of freshwater decapod crustaceans (crabs and shrimps) from Colombia by using a dataset containing 964 digitized records and 13 881 specimens collected between 1910 and 2016, information that has been assembled with data from 21 museums and other institutions worldwide. The characterization of species diversity is based on the estimation of relative abundance of species and it is calculated in three separate analyses in which the data were partitioned as follows: (a) by decapod families (six in Colombia) (b) the unpartitioned dataset of all 139 Colombian species and (c) by the five biogeographic regions in the country. In each case, Campos & Isaza’s species diversity index and the Shannon entropy index were calculated. The calculations performed here also allowed the identification of predominant species and those that are least represented in collections and might therefore be at greater risk of extinction.

Are Filopodia Privileged Signaling Structures in Migrating Cells?

Filopodia are thin, fingerlike structures that contain bundled actin filaments and project from the cell periphery. These structures are dogmatically endowed with the ability to sense cues in the microenvironment, implying that filopodia foster local signal transduction, yet their small diameter hampers the imaging of dynamic processes therein. To overcome this challenge, we analyzed total internal reflection fluorescence images of migrating fibroblasts coexpressing either a plasma membrane marker or tagged AktPH domain, a translocation biosensor for signaling through the phosphoinositide 3-kinase pathway, along with a cytosolic volume marker. We devised a scheme to estimate the radii of filopodia using either the membrane marker or volume marker data, and we used that information to account for geometry effects in the biosensor data. With conservative estimates of relative target molecule abundance, it is revealed that filopodia typically harbor higher densities of 3′ phosphoinositides than adjacent regions at the cell periphery. In this context at least, the analysis supports the filopodial signaling hypothesis.

Maternal effects and Symbiodinium community composition drive differential patterns in juvenile survival in the coral Acropora tenuis.

Coral endosymbionts in the dinoflagellate genus Symbiodinium are known to impact host physiology and have led to the evolution of reef-building, but less is known about how symbiotic communities in early life-history stages and their interactions with host parental identity shape the structure of coral communities on reefs. Differentiating the roles of environmental and biological factors driving variation in population demographic processes, particularly larval settlement, early juvenile survival and the onset of symbiosis is key to understanding how coral communities are structured and to predicting how they are likely to respond to climate change. We show that maternal effects (that here include genetic and/or effects related to the maternal environment) can explain nearly 24% of variation in larval settlement success and 5–17% of variation in juvenile survival in an experimental study of the reef-building scleractinian coral, Acropora tenuis. After 25 days on the reef, Symbiodinium communities associated with juvenile corals differed significantly between high mortality and low mortality families based on estimates of taxonomic richness, composition and relative abundance of taxa. Our results highlight that maternal and familial effects significantly explain variation in juvenile survival and symbiont communities in a broadcast-spawning coral, with Symbiodinium type A3 possibly a critical symbiotic partner during this early life stage.

Ecology and local knowledge of the Baird's tapir (Tapirella bairdii) in the Sierra Madre de Oaxaca, Mexico.

As well as being of global cultural importance (from local tribal folklore to being an iconic species for conservation), the tapir plays an important role in its ecosystem as a herbivore and seed disperser. However, the ecology and ethnozoology of the endangered Baird's tapir in the north of Oaxaca, Mexico is poorly understood. We used camera traps to estimate its relative abundance and density and to describe the activity patterns of the northernmost population of Baird's tapir in the Sierra Madre de Oaxaca. Local knowledge concerning the tapir was also documented, along with the conservation strategies undertaken by the 2 indigenous communities that own the land where the study site is located. Only adult tapirs were photographed, and these were active 14 h per day, but were mainly nocturnal and crepuscular. The estimated relative abundance (12.99 ± 2.24 events/1000 camera days) and density values (0.07-0.24 individuals/km(2) ) were both similar to those found in another site in Mexico located within a protected area. Semi-structured interviews revealed that people have a basic understanding of the eating habits, activity and main predators of the tapir. There were reports of hunting, although not among those respondents who regularly consume bush meat. Thus, the relative abundance and density estimates of tapir at the study site could be related to the favorable condition of the forest and the absence of hunting and consumption of tapir meat. Fortunately, the local people are conducting initiatives promoting the conservation of this ungulate and its habitat that combine to constitute a regional trend of habitat and wildlife protection.

A spatial–temporal double-hurdle model for extremely over-dispersed avian count data

Several wind energy facilities are currently being planned for offshore Atlantic waters of the United States. However, relatively little is known about the distribution, abundance and spatio-temporal variability of marine birds in their offshore habitats and it is becoming increasingly necessary to accurately characterize these demographic parameters before assessing the influence of factors such as offshore energy development on populations. Thus, we incorporate a multi-scale approach to develop models for the space-time distribution and abundance of marine birds to identify potential high-use areas in need of further study. With data taken from past and ongoing survey efforts, we provide relative abundance and density estimates for marine birds over a wide geographical area during multiple years. Due to the excessive amount of zeros as well as extremely large counts exhibited in the data, a double-hurdle model is formulated that includes a negative binomial and a generalized Pareto distribution mixture. Spatial heterogeneity is modeled using a conditional auto-regressive (CAR) prior, and a Fourier basis was used for seasonal variation. We demonstrate our model by creating probability maps that show areas of high-abundance and aggregation for twenty-four species of marine bird.

Density-dependent effects as key drivers of intraspecific size structure of six abundant fish species in lakes across Europe

We studied fish size structure by using mean size, size diversity, and the slope of linear size spectra of six common European fish species along large-scale environmental gradients. We further analyzed the response of these three size metrics to environmental variables and to density-dependent effects, i.e., relative estimates of abundance (catch per unit effort, CPUE). We found differences in the strength of main predictors of size structure between the six species, but the direction of the response was relatively similar and consistent for most of the size metrics. Mean body size was negatively related to temperature for perch (Perca fluviatilis), roach (Rutilus rutilus), and ruffe (Gymnocephalus cernuus). Lake productivity (expressed as total phosphorus concentration) and lake depth were also predictors of size structure for four of six species. Moreover, we found a strong density dependence of size structure for all species, resulting in lower mean body size and size diversity and steeper size spectra slopes when density dependence increases. This suggests that density dependence is a key driver of fish size structure.

Insights from baited video sampling of temperate reef fishes: How biased are angling surveys?

The need to address biodiversity information requirements has led to ‘methods research’ growing significantly in the field of ecology. Optimizing inference from survey data is dependent upon understanding the extent of sampling bias, which is inevitable when a subsample is taken to represent the entire population. In this study, angling is compared to Baited Remote Underwater Stereo–Video systems (stereo-BRUVs) as fisheries-independent sampling techniques for surveying temperate reef fishes in the Tsitsikamma Marine Protected Area, South Africa. The comparison highlighted a number of differences in the observed ichthyofauna, notably the ability of stereo-BRUVs to sample a wider range of species while also providing a more consistent index of relative abundance. Comparing relative abundance estimates indicated that both sampling methods were, in general, detecting similar environmentally-induced trends. Size distribution data from the two methods differed significantly amongst the predominant species, and angling produced consistently larger length–frequencies than stereo-BRUVs. However, when the hook-based size selectivity of angling was taken into account, there were no significant differences between the two methods. The ability to detect a species-specific population change over a period of five years was assessed using power analyses, and stereo-BRUVs consistently outperformed angling. The results identify stereo-BRUVs as the superior technique for monitoring the population and size-structure of temperate reef fishes.

Modelling the relative abundance of the primary African vectors of malaria before and after the implementation of indoor, insecticide-based vector control.

BackgroundMalaria remains a heavy burden across sub-Saharan Africa where transmission is maintained by some of the world’s most efficient vectors. Indoor insecticide-based control measures have significantly reduced transmission, yet elimination remains a distant target. Knowing the relative abundance of the primary vector species can provide transmission models with much needed information to guide targeted control measures. Moreover, understanding how existing interventions are impacting on these relative abundances highlights where alternative control (e.g., larval source management) is needed.MethodsUsing the habitat suitability probabilities generated by predictive species distribution models combined with data collated from the literature, a multinomial generalized additive model was applied to produce relative abundance estimates for Anopheles arabiensis, Anopheles funestus and Anopheles gambiae/Anopheles coluzzii. Using pre- and post-intervention abundance data, estimates of the effect of indoor insecticide-based interventions on these relative abundances were made and are illustrated in post-intervention maps.ResultsConditional effect plots and relative abundance maps illustrate the individual species’ predicted habitat suitability and how they interact when in sympatry. Anopheles arabiensis and An. funestus show an affinity in habitat preference at the expense of An. gambiae/An. coluzzii, whereas increasing habitat suitability for An. gambiae/An. coluzzii is conversely less suitable for An. arabiensis but has little effect on An. funestus. Indoor insecticide-based interventions had a negative impact on the relative abundance of An. funestus, and a lesser effect on An. arabiensis. Indoor residual spraying had the greatest impact on the relative abundance of An. funestus, and a lesser effect on An. gambiae/An. coluzzii. Insecticide-treated bed nets reduced the relative abundance of both species equally. These results do not indicate changes in the absolute abundance of these species, which may be reduced for all species overall.ConclusionsThe maps presented here highlight the interactions between the primary vector species in sub-Saharan Africa and demonstrate that An. funestus is more susceptible to certain indoor-based insecticide interventions than An. gambiae/An. coluzzii, which in turn, is more susceptible than An. arabiensis. This may provide An. arabiensis with a competitive advantage where it is found in sympatry with other more endophilic vectors, and potentially increase the need for outdoor-based vector interventions to deal with any residual transmission barring the way to malaria elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1187-8) contains supplementary material, which is available to authorized users.

Temporal partial unmixing of exotic salt cedar using Landsat time series

ABSTRACTIn the south-western United States, the rapid colonization of exotic salt cedar (Tamarix spp.) along the riparian corridors poses a serious threat to the native plant diversity. Monitoring the salt cedar abundance in diversified riparian ecosystems is critically essential for evaluating the biodiversity loss and developing corresponding restoration strategies. To date, it still remains a significant challenge to estimate the abundance of plant species within a pixel, as many plants share similar spectral signatures. This challenge is even more daunting in species diverse ecosystems due to the difficulty of securing all the endmembers (e.g. plant species) in unmixing procedures. The objective of this study is to introduce a new concept, temporal partial unmixing, to estimate the relative abundance of plant species using Landsat time series. Temporal partial unmixing only requires the signature of the target endmember, but it emphasizes the importance of the temporal dimension of the target signature in estimating the corresponding abundance. Two types of temporal signatures that capture the phenological trajectory of the salt cedar growth were devised in this study. Compared to the traditional partial unmixing method (R2 = 0.35), temporal partial unmixing that exploited the temporal signatures greatly improved the relative abundance estimation accuracy (R2 = 0.56 or 0.49). It is concluded that the proposed temporal partial unmixing, along with the readily available Landsat imagery, offers unprecedented opportunities to monitor the abundance dynamics of plant species, especially in spatially heterogeneous landscapes.

Optimization and accuracy of faecal pellet count estimates of population size: The case of European rabbits in extensive breeding nuclei

Cost-effective indices to estimate relative abundances of species are crucial for their management and conservation. As an example, population indices are needed to monitor extensive breeding nuclei used for translocating wild rabbit populations. Based on counts of faecal pellets from four high density rabbit nuclei in southwest Spain: (i) we assess the accuracy of this population index in high-density populations; and (ii) present a simulation approach to evaluate how the reduction of the counting effort affects accuracy of the population estimates. Our findings suggest that this method provides a valid estimate in high-density rabbit populations, and, notably, estimates would have not substantially changed after a reduction of 45–65% in the number of counted plots depending on variation on rabbit density between nuclei. We provide a framework that managers and other scientists could use to improve data collection of pellet counts in order to optimize their chances of detecting relative abundance estimates of rabbits. In addition, we present a R function to implement our approach that can easily be applied in a variety of monitoring programmes for other species based on count data. This will likely help to reduce field-effort in different studies without compromising population indices estimates.