Savanna ecosystems are challenging to map and monitor as their vegetation is highly dynamic in space and time. Understanding the structural diversity and biomass distribution of savanna vegetation ...requires high-resolution measurements over large areas and at regular time intervals. These requirements cannot currently be met through field-based inventories nor spaceborne satellite remote sensing alone. UAV-based remote sensing offers potential as an intermediate scaling tool, providing acquisition flexibility and cost-effectiveness. Yet despite the increased availability of lightweight LiDAR payloads, the suitability of UAV-based LiDAR for mapping and monitoring savanna 3D vegetation structure is not well established. We mapped a 1 ha savanna plot with terrestrial-, mobile- and UAV-based laser scanning (TLS, MLS, and ULS), in conjunction with a traditional field-based inventory (n = 572 stems > 0.03 m). We treated the TLS dataset as the gold standard against which we evaluated the degree of complementarity and divergence of structural metrics from MLS and ULS. Sensitivity analysis showed that MLS and ULS canopy height models (CHMs) did not differ significantly from TLS-derived models at spatial resolutions greater than 2 m and 4 m respectively. Statistical comparison of the resulting point clouds showed minor over- and under-estimation of woody canopy cover by MLS and ULS, respectively. Individual stem locations and DBH measurements from the field inventory were well replicated by the TLS survey (R2 = 0.89, RMSE = 0.024 m), which estimated above-ground woody biomass to be 7% greater than field-inventory estimates (44.21 Mg ha−1 vs 41.08 Mg ha−1). Stem DBH could not be reliably estimated directly from the MLS or ULS, nor indirectly through allometric scaling with crown attributes (R2 = 0.36, RMSE = 0.075 m). MLS and ULS show strong potential for providing rapid and larger area capture of savanna vegetation structure at resolutions suitable for many ecological investigations; however, our results underscore the necessity of nesting TLS sampling within these surveys to quantify uncertainty. Complementing large area MLS and ULS surveys with TLS sampling will expand our options for the calibration and validation of multiple spaceborne LiDAR, SAR, and optical missions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Harvests from recreational fishing are increasingly as important as commercial harvest to populations of popularly fished marine recreational species. However, it has yet to be determined whether the ...increasing importance of recreational fishing is a general trend of marine fisheries in the US or whether such a trend is limited to only those species recognized as popular recreational fishes. 71% of marine species in the US have experienced an increase in the proportion of total harvest from the recreational sector during the time harvest data are available for both sectors. Species demonstrating an increase in the proportion of harvests by the recreational sector included those generally regarded as commercial, bait, and bycatch species, as well as those considered recreational species. Marine species categorized as overfished could not be predicted from either fishery characteristics or life history characteristics in a PCA analysis of available data for fished species in the US. Consequently, there appears to be little to predict vulnerability of populations to fishing efforts save that all fished species can be made vulnerable to overexploitation. Well-developed yield-based strategies, designed for commercial fisheries, are not likely to be effective in managing populations as the diverse recreational fishing sector continues to increase in its importance. Thus, new management strategies for US marine fisheries are needed. Some possible alternative strategies are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Negative interactions between waterbirds and people are increasing. Waterbirds feeding on agricultural crops cause significant losses to farmers worldwide, but so far most research to address these ...conflicts has been conducted on migratory species in the temperate northern hemisphere. We investigated the space use and habitat selection of the magpie goose (Anseranas semipalmata), a taxonomically distinct waterbird endemic to Australia and southern Papua New Guinea. In tropical northern Australia, magpie geese are protected but are increasingly persecuted by farmers to protect crops during the late dry–early wet season (~Sep–Jan), a bottleneck of natural resources for waterbirds in the monsoonal tropics. Using satellite telemetry of 38 geese spread across 3 seasons (2016–2017, 2017–2018, 2018–2019), we evaluated daily and seasonal space use, individual site fidelity, and habitat selection to determine the extent of use of agricultural fields by geese, and the spatiotemporal scales at which management should be undertaken. Geese used relatively small daily areas (x̄ = 8.2 km2) consistently throughout the late dry–early wet season, and repeatedly used agricultural fields, forested bushlands, and local wetlands. Geese used comparatively large seasonal areas (x̄ = 219.5 km2) encompassing several agricultural areas, and had a low mean overlap between successive weekly core activity areas, indicating that site fidelity rapidly weakened over time. These results suggest that farm‐scale (<30 ha) management of geese is unlikely to be effective because hazed individuals are likely to be replaced soon afterwards. Instead, our findings suggest that goose management should be coordinated strategically at the local (~1,000 ha), or regional (~100,000 ha) scale. Farm‐level management would likely be more effective if implemented in conjunction with the creation of regional sanctuaries where geese could rest and potentially feed undisturbed away from farms. Our findings can be used by wildlife managers for optimizing the location of such sanctuaries and highlight the necessity for management to be adaptive given the opportunistic nature of the species.
We investigated the space use and habitat selection of tropical magpie geese to determine the extent of use of agricultural fields and to evaluate appropriate spatiotemporal scales for management. Geese used space opportunistically and preferentially selected irrigated agricultural fields over other land cover types, highlighting that management efforts will benefit from being adaptive, coordinated at the regional scale, and implemented in conjunction with the creation of disturbance‐free sanctuaries for geese.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The maturity of remote sensing and ecosystem restoration science provides new opportunities to monitor and assess ecosystem indicators at finer resolutions and at suitable scales. A key link in ...joining these fields is creating a framework to apply these rich datasets to ecosystem restoration projects. Savanna woodland ecosystems have discontinuous tree cover that is an important, but potentially highly variable, structural component of these ecosystems. Woody cover in savannas is also well suited to being measured with remote sensing techniques. We extracted woody cover from a 66‐yr time series of aerial imagery covering 1718 ha of mesic savanna ecosystem in northern Australia, adjacent to the Ranger uranium mine and encompassing portions of Kakadu National Park. This ecosystem is proposed as a reference ecosystem that may be used to comparatively assess and monitor restoration trajectories of the mine site in the coming decades. The spatiotemporal patterns of change in woody cover were assessed at spatial extents similar to the mine site. We were able to construct a robust distribution of canopy cover values and associated spatial heterogeneity that can be used to set closure criteria, inform restoration trajectories, and guide monitoring activities for the restored mine site.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Atlantic croaker is one of the most abundant demersal fish in Chesapeake Bay. Until recently, when substantial declines in abundance have occurred, high biomass supported elevated fisheries landings. ...Therefore, study of the diet of Atlantic croaker is important to understand its own dynamics and its role in the Chesapeake Bay ecosystem. Patterns in the diet of croaker varied annually, seasonally, and spatially, but were not strongly correlated with any measured environmental variables. Although the majority of the diet of croaker consisted of polychaetes and other benthic items, about 20% of the croaker diet by weight consisted of anchovy and other fishes. Croaker consumption of anchovy is likely a result of crepuscular feeding that has not been captured in previous studies that sampled during the day and with bottom trawls. Thus, croaker influences both the benthic and pelagic components of the Chesapeake Bay food web and incorporating such diel patterns in diet may increase the reliability of fishery ecosystem models.
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•Spectra of savanna understorey vegetation species over phenological seasons.•Separability of functional groups, and species, depended on season.•Informs species separation and timing ...for drone-based hyperspectral captures.•VNIR drone spectral range excludes foliar traits such as cellular water absorption.
The relationship between species phenology and spectral separability is essential to determine the optimal remote sensing sampling period to maximise spectral separability of vegetation species. However, this relationship in many native grasses, introduced grasses and herbs, shrubs, and vine species in tropical savannas is unknown. We measured the in-situ hyperspectral response of monospecific vegetation stands of several understorey species representing different functional groups over phenological stages (throughout dry and wet seasons) using a non-imaging spectrometer. We present a spectral library of both native and introduced species of a tropical savanna environment. We analysed the data using continuum removal to highlight absorption features. Most understorey species displayed a photosynthetic spectral response with increased greenness at the end of the wet season that progressively declined as vegetation dried out. For some species, there were seasonally dependent differences in absorption features with spectral differences between the late wet and early dry season, and late dry and early wet seasons. We resampled the data to the spectral range typical of drone-mounted hyperspectral sensors (i.e., 150 bands between 400 and 1000 nm), which omits the water absorption features of the SWIR. These findings suggest an ideal sampling period for measuring outdoor canopy reflectance of understorey species, which will promote methodological improvements of hyperspectral data capture. The use of a VNIR only hyperspectral sensor will exclude the important regions of the spectrum for plant spectral identification including non-pigment bands for water, nitrogen and cellulose. The results have implications for determining the completeness of rehabilitation assessing reestablishment among indigenous species across mine sites under rehabilitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The miniaturisation of hyperspectral sensors for use on drones has provided an opportunity to obtain hyper temporal data that may be used to identify and monitor non-native grass species. However, a ...good understanding of variation in spectra for species over time is required to target such data collections. Five taxological and morphologically similar non-native grass species were hyper spectrally characterised from multitemporal spectra (17 samples over 14 months) over phenological seasons to determine their temporal spectral response. The grasses were sampled from maintained plots of homogenous non-native grass cover. A robust in situ standardised sampling method using a non-imaging field spectrometer measuring reflectance across the 350–2500 nm wavelength range was used to obtain reliable spectral replicates both within and between plots. The visible-near infrared (VNIR) to shortwave infrared (SWIR) and continuum removed spectra were utilised. The spectra were then resampled to the VNIR only range to simulate the spectral response from more affordable VNIR only hyperspectral scanners suitable to be mounted on drones. We found that species were separable compared to similar but different species. The spectral patterns were similar over time, but the spectral shape and absorption features differed between species, indicating these subtle characteristics could be used to distinguish between species. It was the late dry season and the end of the wet season that provided maximum separability of the non-native grass species sampled. Overall the VNIR-SWIR results highlighted more dissimilarity for unlike species when compared to the VNIR results alone. The SWIR is useful for discriminating species, particularly around water absorption.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Waterbirds commonly undertake extensive movements in search of resources. While much is known about waterbird movements within temperate regions where resource distribution is seasonally predictable, ...less is understood about waterbird movements in tropical and subtropical environments where the temporal distribution of resource is less predictable. This knowledge is critical to understanding a species' response to environmental and anthropogenic changes to natural habitats. Here, we investigated the movement behaviour of a tropical waterbird of northern Australia, the Magpie Goose (Anseranas semipalmata), seasonally utilising a recently developed mixed natural-anthropogenic landscape. Using satellite telemetry, we assessed the daily movements and space use of 18 individuals (4673 goose-days) to determine whether these individuals spent the year locally, migrated seasonally from further areas, or were transitory individuals from across northern Australia. Geese released from peri-urban and rural areas in the late dry season dispersed to both local (≤ 50 km) and distant (≤ 566 km) floodplain systems over the wet season. Tracked individuals returned to sites within the same floodplain systems in the wet season and within the same anthropogenic areas in the late dry season over consecutive years. Our results suggest that anthropogenic environments may provide predictable resources for Magpie Geese during a seasonal bottleneck of natural resources. We highlight the need to learn more about waterbird movement behaviour within tropical human-dominated landscapes to evaluate the likelihood that predictable resources could exacerbate human-wildlife conflicts, and the possible long-term effects on species population dynamics, behaviour and distribution.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
When RNA purified from sea urchin embryos is fractionated by the addition of LiCl to 2 molar, low molecular weight (LMW) RNA is partitioned into both the soluble (S) and insoluble (P) fractions. The ...S fraction contains most of the LMW RNA. S and P fraction RNA was isolated from embryos which had been incubated with radioactive nucleotide precursors for 30 min to 2 hours. Electrophoresis of this RNA on 15% acrylamide gels containing 7M urea results in most of the radioactivity being found in two peaks; one centered at 4S (peak I), and the other at approximately 4.5S (peak II). Four classes of 4- to 5S RNA are thus defined on the basis of salt solubility and molecular weight, and are designated SI, SII, PI, and PII. Chain length estimates of these RNA classes based on the mobility of E coli tRNA and 55 RNA are as follows: SI, 75 nucleotides; SII, 95 nucleotides; PI, 78 nucleotides, and PII, 100 nucleotides. On the basis of several criteria, SI is comprised of tRNA, and SII and PII appear to contain two classes of precursor tRNA; PI contains 'tRNA-like' molecules and may either represent precursor molecules in the final stages of maturation, or a class of tRNAs distinguishable from the major portion of tRNAs in a number of characteristics. All four classes of RNA are highly methylated, possess tRNA-like base compositions, and contain a spectrum of modified nucleotides characteristic of tRNA. The levels of methylation of RNA in the SII and PII fractions are lower than those in SI and PI, which are similar to each other. All four of these RNA fractions are represented in nuclei, although the fraction of total RNA which is nuclear may differ between the S and P fractions. A comparison of the modified nucleotide content of these RNA fractions isolated from nuclei and whole cells suggest that most of the nucleotide modifications occur within the nucleus. A detailed analysis of the kinetics of synthesis and turnover of these RNA fractions was made for cleavage, blastula, gastrula, and pluteus stage embryos. SII and PII RNAs were unstable and turned over with half lives of about 20- and 10 min, respectively. SI and PI molecules were stable, except in cleavage stage embryos where PI RNA was unstable. The rates of synthesis of all four RNAs was several fold lower in cleavage stage embryos compared to those in blastula stage embryos. The synthesis and processing of S and P fraction RNAs appeared to be regulated independently. While the rate of synthesis of SII RNA and the rate of accumulation of RNA in SI were similar in the three later stage embryos, those of PII and PI RNAs decreased several fold during development. There appeared to be quantitative processing of SII molecules to RNA found in fraction SI, with all of the RNA accumulating in SI derived from processing of SII molecules. This was not the case for the P fraction where there appeared to be a progressively increasing 'overproduction' of PII RNA with respect to the accumulation of PI molecules during development. Several additional kinetic properties of these RNAs are discussed. A comparison of the conformations of the four RNA fractions as probed by hydroxyapatite chromatography and SI nuclease digestion indicated that SII and PII molecules possessed conformations distinct from each other, whereas those of SI and PI molecules were quite similar.
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