1,720,973 research outputs found
Physiological mechanisms underlying fish distributions along elevational gradients: estimating fundamental thermal niches
No full textSubmission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Ecology, Environment and Evolution, School of Life Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora.There is much concern about how climate change will affect the thermal regimes of freshwater ecosystems and, by extension, the performance of ectothermic animals within those systems. The aim of this PhD thesis was to improve our understanding of the thermal niches of two congeneric species of fish distributed along elevational gradients: the river blackfish (Gadopsis marmoratus), and two-spined blackfish (G. bispinosus). By studying the thermal niches of these two species, this thesis aimed to 1) determine whether the distributions of the blackfish are constrained by their thermal physiology, and 2) determine how changes in thermal regimes predicted by climate change will impact these two species. The distribution of the two species, and associated temperature regimes suggest they have different realized thermal niches, with G. bispinosus occupying cooler habitats than G. marmoratus. Despite this, there were only small differences in their thermal niche when defined by aerobic swimming performance, aerobic scope, growth rate and thermal tolerance. Predictions of how increasing temperatures due to climate change may impact these two species were made based on temperature-dependent growth models and upper thermal limits (UTL). The impact of increasing temperatures on growth rates were highly seasonally specific, with strong decreases predicted for summer. These reductions in growth will occur during the recruitment season, which may result in blackfish distribution contracting to higher elevations. Additionally, climate change is likely to cause maximum temperatures to frequently exceed blackfish UTLs across large parts of their distribution. This thesis demonstrates that modelling the thermal niches of ectotherms distributed along the river continuum is not straightforward. If we are to effectively and efficiently forecast impacts of different thermal futures, riverine ecologists must do more to experimentally decipher the relative influence of temperature and other abiotic drivers on the fitness of riverine ectotherms.This thesis was a recipient of the Nancy Millis Award for theses of exceptional merit
Using citizen science to test for acoustic niche partitioning in frogs
Full text linkThe acoustic niche hypothesis proposes that to avoid interference with breeding signals, vocal species should evolve to partition acoustic space, minimising similarity with co-occurring signals. Tests of the acoustic niche hypothesis are typically conducted using a single assemblage, with mixed outcomes, but if the process is evolutionarily important, a pattern of reduced acoustic competition should emerge, on average, over many communities. Using a continental-scale dataset derived from audio recordings collected by citizen scientists, we show that frogs do partition acoustic space. Differences in calls were predominately caused by differences in spectral, rather than temporal, features. Specifically, the 90% frequency bandwidths of observed frog assemblages overlapped less than expected, and there was greater distance between dominant frequencies than expected. To our knowledge, this study is the first to use null models to test for acoustic niche partitioning over a large geographic scale
Spectral overlap and temporal avoidance in a tropical savannah frog community
No full textVocalizing animals often occur in complex acoustic environments where there is a high chance of acoustic interference from co-occurring species with spectrally overlapping vocalizations. Acoustic interference impedes detection and discrimination of signals, and may ultimately reduce fitness. The aim of this study was to determine the relationship between spectral overlap and temporal overlap in a tropical savannah frog community. We predicted that species pairs that overlap spectrally would behaviourally respond to one another by avoiding calling at the same time, to minimize acoustic interference. We determined the calling activity of 14 frog species at four locations across 4 months during peak breeding season. We then determined the difference between observed and expected temporal overlap for all species pairs as a function of spectral overlap at three temporal scales (night-minute-call). There was potential for acoustic interference between many of the species studied with the calls of up to half of the species pairs at each site overlapping spectrally. There was no relationship between spectral overlap and observed–expected temporal overlap at either the night or minute level. Instead, calling activity was aggregated at both the night and minute level. Evidence of a negative relationship between spectral overlap and temporal overlap was found at the call level, with species pairs with greater mean spectral overlap calling together less frequently than expected. The observed aggregated calling at the night and minute level suggest that at gross timescales, factors other than avoiding spectral overlap are driving calling activity in tropical savannah frog communities. The call level avoidance found in this study may be sufficient for spectrally overlapping species pairs to avoid the negative effects of acoustic interference, allowing them to call during the same nights and at similar times to take advantage of favourable environmental conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Towards automated detection of the endangered southern black-throated finch (Poephila cincta cincta)
No full textContext
Biodiversity is declining worldwide, with many species decreasing in both number and range. Acoustic monitoring is rapidly becoming a common survey method in the ecologist’s toolkit that may aid in the conservation of endangered species, but effective analysis of long-duration audio recordings is still challenging.
Aims
The aims of this study were to: (1) develop and test call recognisers for the endangered southern black-throated finch (Poephila cincta cincta) as well as the similar sounding, but non-endangered, double-barred finch (Taeniopygia bichenovii); and (2) compare the ability of these recognisers to detect these species with that of on-ground bird surveys at under-surveyed locations in the Desert Uplands bioregion which is at the edge of the known range of the black-throated finch.
Methods
A range of convolutional neural network call recognition models were built and tested for both target species, before being deployed over new audio recordings collected at 25 sites during 2020, 2021 and 2022, and compared with the results of on-ground bird surveys at those same sites.
Key results
Call recognisers for both species performed well on test datasets from locations in the same area as the training data with an average area under the precision-recall curve (PRAUC) of 0.82 for black-throated finch and 0.87 for double-barred finch. On-ground bird surveys in the Desert Uplands bioregion detected black-throated finches at two locations in different years, and our call recognisers confirmed this with minimal post-validation of detections. Similar agreement between methods were obtained for the double-barred finch, with site occupancy in the Desert Uplands bioregion confirmed with audio recognition in all nine surveys with on-ground detections, as well as during four additional surveys that had no on-ground detections.
Conclusions
Using call recognisers to survey new locations for black-throated finch presence was equally successful as on-ground surveys, and with further refinements, such as retraining models with examples of commonly misclassified vocalisations added to the training data, minimal validation should be required to detect site presence.
Implications
Acoustic monitoring should be considered as a valuable tool to be used alongside manual surveys to allow effective monitoring and conservation of this endangered species
An Optimised Grid Search Based Framework for Robust Large-Scale Natural Soundscape Classification
No full textLarge-scale natural soundscapes are remarkably complex and offer invaluable insights into the biodiversity and health of ecosystems. Recent advances have shown promising results in automatically classifying the sounds captured using passive acoustic monitoring. However, the accuracy performance and lack of transferability across diverse environments remains a challenge. To rectify this, we propose a robust and flexible ecoacoustics sound classification grid search-based framework using optimised machine learning algorithms for the analysis of large-scale natural soundscapes. It consists of four steps: pre-processing including the application of spectral subtraction denoising to two distinct datasets extracted from the Australian Acoustic Observatory, feature extraction using Mel Frequency Cepstral Coefficients, feature reduction, and classification using a grid search approach for hyperparameter tuning across classifiers including Support Vector Machine, k-Nearest Neighbour, and Artificial Neural Networks. With 10-fold cross validation, our experimental results revealed that the best models obtained a classification accuracy of 96% and above in both datasets across the four major categories of sound (biophony, geophony, anthrophony, and silence). Furthermore, cross-dataset validation experiments using a pooled dataset highlight that our framework is rigorous and adaptable, despite the high variance in possible sounds at each site
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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