Applications of bioacoustics in animal ecology

In communication animals use a full range of signals: acoustic, visual, chemical, electrical and tactile. The processes involved in how and why animals communicate have long held veritable fascination for scientists. A branch of science concerned with the production of sound and its effects on living organisms is bioacoustics.The main purpose of the present study is to raise and discuss some issues related to the relationship between animals, their sounds and ecology, including presentation of methods of analysis of sound recordings. A better understanding of the relationship between the studied animals will allow for development of a better framework for future research, as well as a better grasp of interactions between different organisms, including humans. The paper discusses the significance of acoustic research in animal ecology and its possible applications in the future. The author also summarizes previous research in the field of sound communication of various animal species.The paper proves that vocalizations of every acoustically communicating animal are threatened by climate change. For marine animals, the source of changes in vocalization abilities is ocean acidification and increased ambient noise, which can affect communication and foraging behavior. For terrestrial animals, changes in precipitation and temperature may result in modifications of the sounds emitted, as well as certain modifications to the auditory system. Together with changes in species distribution due to environmental parameters, cumulatively these factors can cause changes in the entire landscape of acoustics ecosystems. Thanks to acoustic biomonitoring, we can understand how the sounds of entire habitats and acoustic ecosystems will change in response to the changing climate and how it will affect bioacoustics on a global scale.     

Relationships between survival and habitat suitability of semi‐aquatic mammals

Spatial distribution and habitat selection are integral to the study of animal ecology. Habitat selection may optimize the fitness of individuals. Hutchinsonian niche theory posits the fundamental niche of species would support the persistence or growth of populations. Although niche‐based species distribution models (SDMs) and habitat suitability models (HSMs) such as maximum entropy (Maxent) have demonstrated fair to excellent predictive power, few studies have linked the prediction of HSMs to demographic rates. We aimed to test the prediction of Hutchinsonian niche theory that habitat suitability (i.e., likelihood of occurrence) would be positively related to survival of American beaver (Castor canadensis), a North American semi‐aquatic, herbivorous, habitat generalist. We also tested the prediction of ideal free distribution that animal fitness, or its surrogate, is independent of habitat suitability at the equilibrium. We estimated beaver monthly survival probability using the Barker model and radio telemetry data collected in northern Alabama, United States from January 2011 to April 2012. A habitat suitability map was generated with Maxent for the entire study site using landscape variables derived from the 2011 National Land Cover Database (30‐m resolution). We found an inverse relationship between habitat suitability index and beaver survival, contradicting the predictions of niche theory and ideal free distribution. Furthermore, four landscape variables selected by American beaver did not predict survival. The beaver population on our study site has been established for 20 or more years and, subsequently, may be approaching or have reached the carrying capacity. Maxent‐predicted increases in habitat use and subsequent intraspecific competition may have reduced beaver survival. Habitat suitability‐fitness relationships may be complex and, in part, contingent upon local animal abundance. Future studies of mechanistic SDMs incorporating local abundance and demographic rates are needed.     

激光雷达技术在动物生态学领域的研究进展

激光雷达(light detection and ranging, LiDAR)作为一门新兴的主动遥感技术, 近年来由于在提取和反演森林参数水平上不断提高, 被越来越多地应用于动物生态学研究中。本文通过整理和搜集国内外文献, 对激光雷达的技术特点及其在森林参数提取和动物生境上的研究进展进行综述, 指出当前基于LiDAR的森林参数反演算法主要服务于森林资源调查或林学研究, 缺少对动物生态或生理意义相关的参数量化信息。目前该技术在国内的动物生态学方面的应用较少, 尚未见文章发表。通过总结国外学者的研究, 分别从动物生境选择与三维森林结构的关系、栖息地立体生境制图、生物多样性评估和物种分布模型预测三个方面综述了LiDAR在动物生态学研究中的应用现状。相比传统方法, LiDAR技术提供的高精度三维结构信息, 能够显著提高动物生境质量的评估、生物多样性的监测水平和物种分布模型的评价精度, 有利于从机理上加深对物种生境选择和集群过程的理解。但目前LiDAR技术的应用主要集中在对已知的生态关系研究, 尤其是冠层结构与动物分布的关系, 缺少对林下层生活的动物生境质量和生物多样性的监测和评估, 同时很多有关动物生存和繁衍与立体生境的关系研究有待从LiDAR数据中进一步挖掘分析。未来应加强对森林林下层三维信息的提取, 提高林下层动物生境质量和生物多样性的监测水平, 同时建立适用于动物生态和生理意义相关的参数, 为动物生境质量和生物多样性的评估提供标准的量化指标。     

Environmental determinants of amphibian and reptile species richness in China

Understanding the factors that regulate geographical variation in species richness has been one of the fundamental questions in ecology for decades, but our knowledge of the cause of geographical variation in species richness remains poor. This is particularly true for herpetofaunas (including amphibians and reptiles). Here, using correlation and regression analyses, we examine the relationship of herpetofaunal species richness in 245 localities across China with 30 environmental factors, which include nearly all major environmental factors that are considered to explain broad-scale species richness gradients in such theories as ambient energy, water–energy dynamics, productivity, habitat heterogeneity, and climatic stability. We found that the species richness of amphibians and reptiles is moderately to strongly correlated with most of the environmental variables examined, and that the best fit models, which include explanatory variables of temperature, precipitation, net primary productivity, minimum elevation, and range in elevation, explain ca 70% the variance in species richness for both amphibians and reptiles after accounting for sample area. Although water and temperature are important explanatory variables to both amphibians and reptiles, water variables explain more variance in amphibian species richness than in reptile species richness whereas temperature variables explain more variance in reptile species richness than in amphibian species richness, which is consistent with different physiological requirements of the two groups of organisms.     

Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication

Loss of acoustic habitat due to anthropogenic noise is a key environmental stressor for vocal amphibian species, a taxonomic group that is experiencing global population declines. The Pacific chorus frog (Pseudacris regilla) is the most common vocal species of the Pacific Northwest and can occupy human‐dominated habitat types, including agricultural and urban wetlands. This species is exposed to anthropogenic noise, which can interfere with vocalizations during the breeding season. We hypothesized that Pacific chorus frogs would alter the spatial and temporal structure of their breeding vocalizations in response to road noise, a widespread anthropogenic stressor. We compared Pacific chorus frog call structure and ambient road noise levels along a gradient of road noise exposures in the Willamette Valley, Oregon, USA. We used both passive acoustic monitoring and directional recordings to determine source level (i.e., amplitude or volume), dominant frequency (i.e., pitch), call duration, and call rate of individual frogs and to quantify ambient road noise levels. Pacific chorus frogs were unable to change their vocalizations to compensate for road noise. A model of the active space and time (“spatiotemporal communication”) over which a Pacific chorus frog vocalization could be heard revealed that in high‐noise habitats, spatiotemporal communication was drastically reduced for an individual. This may have implications for the reproductive success of this species, which relies on specific call repertoires to portray relative fitness and attract mates. Using the acoustic call parameters defined by this study (frequency, source level, call rate, and call duration), we developed a simplified model of acoustic communication space–time for this species. This model can be used in combination with models that determine the insertion loss for various acoustic barriers to define the impact of anthropogenic noise on the radius of communication in threatened species. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.     

同域分布大熊猫和水鹿生境利用分异特征

野生动物的生境利用特征研究是动物生态学核心问题之一,同域分布动物对生境的利用特征及共存机制是其重要组成部分,也是实现珍稀濒危物种保护与栖息地恢复的基础。基于空间利用和生境因子选择差异研究了卧龙自然保护区同域分布大熊猫(Ailuropoda melanoleuca)和水鹿(Rusa unicolor)的生境利用关系,探讨了同域分布野生动物在生境因子选择和空间利用的分异特征。结果表明:(1)空间利用上,大熊猫和水鹿的空间重叠系数为58.35%,其中,在原始林和次生林生境中的空间重叠系数分别为66.58%和36.64%,二者在原始林中的空间重叠较高;(2)生境因子选择上,大熊猫和水鹿对物理因子的选择有坡位、离小路距离和离水源距离3个变量有显著性差异,对生物因子的选择有乔木密度、灌木盖度、灌木密度、竹林盖度、幼竹密度、幼竹基径、幼竹高度、成竹高度和死竹密度9种变量有显著性差异;(3)大熊猫和水鹿都表现为更偏好原始林生境,但大熊猫对原始林的依赖性更强。分析同域分布动物的生境利用关系有利于深入了解不同动物对资源的空间利用特征及共存机制,可以为保护区制定珍稀野生动物保护和栖息地恢复政策提供科学依据。     

Sounds of shallow water fishes pitch within the quiet window of the habitat ambient noise

The habitat ambient noise may exert an important selective pressure on frequencies used in acoustic communication by animals. A previous study demonstrated the presence of a match between the low-frequency quiet region of the stream ambient noise (termed ‘quiet window’) and the main frequencies used for sound production and hearing by two stream gobies (Padogobius bonelli, Gobius nigricans). The present study examines the spectral features of ambient noise in very shallow freshwater, brackish and marine habitats and correlates them to the range of dominant frequencies of sounds used by nine species of Mediterranean gobies reproducing in these environments. Ambient noise spectra of these habitats featured a low-frequency quiet window centered at 100 Hz (stream, sandy/rocky sea shore), or at 200 Hz (spring, brackish lagoon). The analysis of the ambient noise/sound spectrum relationships showed the sound frequencies matched the frequency band of the quiet window in the ambient noise typical of their own habitat. Analogous ambient noise/sound frequency relationships were observed in other shallow-water teleosts living in similar underwater environments. Conclusions may be relevant to the understanding of evolution of fish acoustic communication and hearing.     

Multi-scale turtle dove nest habitat selection in a Mediterranean agroforestry landscape: implications for the conservation of a vulnerable species

Determination of factors affecting nest habitat selection is a major topic in avian ecology, with strong implications for conservation purposes especially for the species with unfavorable status. The turtle dove (Streptopelia turtur) is a vulnerable species that has undergone a rapid and serious decline across its distribution range. I investigated the effect of different variables at two spatial scales (10-m radius, nest site; and 100-m radius, landscape) on the probability of presence of turtle dove nests in an agroforestry system of Central Morocco. Topography, habitat structure, human disturbance, and land use parameters were measured at nests (n?=?70) and random points (n?=?70) at both scales. Generalized linear model analyses showed that, at the nest site scale, tree height best explained occurrence of turtle dove nests (with nest occurring preferentially in smaller trees). At the landscape scale, nest occurrence probability decreased with elevation and distance to the nearest forest edge, and increased with forest cover and distance to the nearest habitation. Comparison of explanatory power of the single-scale models showed that the most relevant scale was the nest site level, followed by landscape scales, but the model including both nest-scale and landscape-scale variables was best. The variation partitioning analysis confirmed this pattern. In study area, the turtle dove nest habitat selection process occurs within a relatively small scale, but the joint effect of variables at the two scales is relevant. From a practical perspective, it would be interesting to reproduce the same experimental approach on other Mediterranean breeding habitats (agricultural and other forest habitats) to find out if this species would adopt the same nest habitat selection pattern.     

Environmental variation and moose Alces alces density as determinants of spatio-temporal heterogeneity in browsing

Understanding temporal variation in habitat selection and browsing intensity by large herbivores is fundamental because of their large impact on the ecosystems. I studied the annual variation in winter browsing pressure on young trees and habitat selection by moose Alces alces over a ten year period. Specifically, the relationships between browsing pressure on Scots pine Pinus sylvestris and two birch species ( Betula ssp.) and three explanatory variables – 1) availability of forage, 2) moose density (estimated by pellet group counts) and 3) snow cover was studied. At a larger spatial scale (forest stand level) the relationship between moose habitat selection between three different habitat types (forest <30 yr, forest>30 yr and mire) and two explanatory variables, 1) snow condition and 2) moose density, were studied. Browsing pressure on Scots pine, the dominating food plant, was related to forage availability, moose density and snow condition. No significant relationships between any of the three explanatory variables and browsing pressure on the two birch species were found. Moose selection for certain habitats varied between years and was affected by number of days with >0.10 m of snow.
Habitat selection was not significantly related to moose density and the relationship between overall moose density and habitat specific moose densities was proportional within the studied density range. These findings have implications for understanding varying browsing patterns – and will affect both the ability to predict herbivores' effect on the forest ecosystem. A snow dependent browsing pattern also indicates that one can expect a long term decrease in browsing pressure on the tree and shrub layer as a consequence of the ongoing large-scale climate change.     

Using a new framework of two-phase generalized additive models to incorporate prey abundance in spatial distribution models of juvenile slender lizardfish in Haizhou Bay,China

The predictive skill of species distribution models depends on the quality and quantity of input information. In addition to the physical environmental variables, prey availability is also one of the main drivers regulating spatial distribution of marine species. However, prey distribution data have rarely been considered in habitat models due to the lack of information on non-commercial prey species. This may lead to an incomplete view of species distributions and biased model predictions. In this study, we developed a new framework of two-phase generalized additive models (GAMs) based on the Tweedie distribution to incorporate the predicted prey abundance as covariates in habitat models, and applied this framework to juvenile slender lizardfish Saurida elongata in Haizhou Bay, China. This study demonstrated that the predictive skill of habitat models could be greatly improved through incorporating prey abundance as explanatory variables. The importance of prey distribution data in the habitat model confirms the essentiality of including prey data while modelling species distribution. Spatial overlap and GAM analysis demonstrated that not all dominant prey can be selected as potential explanatory variables and only those prey species showing high spatiotemporal occurrences with predators should be incorporated. The framework derived in this study could be extended to other marine organisms to improve the predictive skill of habitat models and enhance our understanding of the ecological mechanisms underlying the distribution of marine species.     

Foraging in space and time structure an African small mammal community

We used live-trapping and foraging to test for the effect of habitat selection and diet on structuring a community of six small mammals and one bird within the Soutpansberg, South Africa. We established grids that straddled adjacent habitats: woodland, rocky hillside, and grassland. Trapping and foraging were used to estimate abundance, habitat use, and species-specific foraging costs. The species with the highest abundance and foraging activity in a habitat, activity time, or food was considered the most efficient and presumed to have a competitive advantage. All species exhibited distinct patterns of spatial and temporal habitat preference which provided the main mechanism of coexistence, followed by diet selection. The study species were organized into three assemblages (α diversity): grassland, Rhabdomys pumilio, Dendromus melanotis, and Mus minutoides.; woodland, Aethomys ineptus and Micaelamys namaquensis; and rock-dwelling, M. namaquensis and Elephantulus myurus. Francolinus natalensis foraged in open rocky areas and under wooded islands within the grassland. Species organization across the habitats suggested that feeding opportunities are available within all habitats; however, distinct habitat preferences resulted from differing foraging aptitudes and efficiencies of the competing species. At Lajuma, species distribution and coexistence are promoted through distinct habitat preferences that were shaped by competition and species-specific foraging costs. The combination of trapping and foraging provided a mechanistic approach that integrates behavior into community ecology by ‘asking’ the animal to reveal its perspective of the environment. Using spatial and temporal foraging decisions—as behavioral indicators—enables us to guide our understanding for across-taxa species coexistence.     

Habitat-dependent song divergence in the little greenbul: an analysis of environmental selection pressures on acoustic signals

Abstract.— Bird song is a sexual trait important in mate choice and known to be shaped by environmental selection. Here we investigate the ecological factors shaping song variation across a rainforest gradient in central Africa. We show that the little greenbul ( Andropadus virens ), previously shown to vary morphologically across the gradient in fitness-related characters, also varies with respect to song characteristics. Acoustic features, including minimum and maximum frequency, and delivery rate of song notes showed significant differences between habitats. In contrast, we found dialectal variation independent of habitat in population-typical songtype sequences. This pattern is consistent with ongoing gene flow across habitats and in line with the view that song variation in the order in which songtypes are produced is not dependent on habitat characteristics in the same way physical song characteristics are. Sound transmission characteristics of the two habitats did not vary significantly, but analyses of ambient noise spectra revealed dramatic and consistent habitat-dependent differences. Matching between low ambient noise levels for low frequencies in the rainforest and lower minimal frequencies in greenbul songs in this habitat suggests that part of the song divergence may be driven by habitat-dependent ambient noise patterns. These results suggest that habitat-dependent selection may act simultaneously on traits of ecological importance and those important in prezygotic isolation, leading to an association between morphological and acoustic divergence. Such an association may promote assortative mating and may be a mechanism driving reproductive divergence across ecological gradients.     

Habitat selection behaviour links local and regional scales in aquatic systems

The role of habitat selection behaviour in the assembly of natural communities is an increasingly important theme in ecology. At the same time, ecologists and conservation biologists are keenly interested in scale and how processes at scales from local to regional interact to determine species distributions and patterns of biodiversity. How important is habitat selection in generating observed patterns of distribution and diversity at multiple spatial scales? In theory, habitat selection in response to interacting species can generate both positive and negative covariances among species distributions and create the potential to link processes of community assembly across multiple scales. Here I demonstrate that habitat selection by treefrogs in response to the distribution of fish predators functions at both the regional scale among localities and the local scale among patches within localities, implicating habitat selection as a critical link between local communities and the regional dynamics of metacommunities in complex landscapes.     

Noise pollution and decreased size of wooded areas reduces the probability of occurrence of Tawny Owl Strix aluco

At present, urban areas cover almost 3% of the Earth's land surface, and this proportion is constantly increasing along with human population growth. Although urbanization leads to biodiversity decline, at the same time it creates a novel and extensive environment that is exploited by whole assemblages of organisms. These include predators, which use the matrix of different habitat types within the urban environment for breeding and/or foraging. This study investigated how attributes of the urban landscape influence the distribution pattern of a nocturnal acoustic predator, the Tawny Owl Strix aluco. The probability of occurrence of this species was correlated with the presence of natural forests, and the increasing size of wooded habitat patches within the urban landscape; however, Tawny Owls were less likely to occur at sites with high noise levels at night. Our study suggests that the distribution pattern of acoustic predators is shaped by the availability of primary habitat but reduced by noise intensity (which may decrease hunting efficiency). The Tawny Owl is a top predator in the urban environment and its presence/absence may therefore affect populations of other species; this provides clear evidence of the indirect effect of noise pollution on animal populations inhabiting urban environments.     

Micro-scale distribution of rabbits on Fuerteventura Island

The European rabbit (Oryctolagus cuniculus) is a conservation and social dilemma in the Canary Islands. It is the main prey of endangered species, it causes severe impacts on vegetation, as well as has a considerable hunting economic value but damages agriculture. We assessed drivers of European rabbit habitat selection on Fuerteventura Island (Canary Islands, Spain) in order to understand the ecology and to contribute with data for managing this introduced species. To measure rabbit abundance, we counted the total number of fresh pellets and latrines. We used Generalized Linear Models (GLMs) to analyze the relationship between rabbit abundance and four groups of variables that represented the biological requirements of the species (environmental, food resources, refuges/shelters, and biological interactions). Hierarchical partitioning techniques were used to estimate the explanatory capacity of these different groups of variables. Our model better explained fresh pellet abundance (89% of total deviance) than latrine abundance (57%). Variables related to food resources best explained the abundance of both latrines and pellets. We identified a set of plant species highly correlated with rabbit abundance, which probably makes up the species’ diet. Variables relating to refuge/shelter and the environmental were also relevant. Interactions with other mammals did not strongly affect rabbit abundance on Fuerteventura Island. Mean annual precipitation and temperature were variables that individually best explained abundance, although half of their relevance is shared with others non-environmental variables. Our results provide policy makers and land-managers with applied information on the relationship between rabbit populations and micro-scale components of Fuerteventura.     

Stream noise,habitat filtering,and the phenotypic and phylogenetic structure of Neotropical anuran assemblages

The structure of assemblages may be determined by interspecific interactions or environmental factors (e.g. competition and habitat filtering). Since communication between conspecific and heterospecific affects fitness of individuals, habitat characteristics that prevent communication could determine habitat use and co-occurrence of species. However, at present there are few studies, most with birds, testing the relationship between sensory ecology and community ecology. Abiotic noise on streams could impede the detection and decoding of auditory signals by receivers through a process named auditory masking. Therefore, we tested the role of abiotic noise on streams as a habitat characteristic influencing the phenotypic and phylogenetic structure of Neotropical anuran assemblages. We tested this hypothesis using data of male body size, call frequency, calling place (alongside and away from streams), and phylogenetic relationship of 110 and 38 anuran species at regional and local scale, respectively. After we found quantitative evidence suggesting that call frequency and body size are conserved phenotypic traits, we found that assemblages alongside streams exhibit both phenotypic and phylogenetic clustering, while assemblages away from streams exhibit both phenotypic and phylogenetic overdispersion. These results offer quantitative evidence suggesting a role of noise on streams promoting a process of habitat filtering and affecting the structure of anuran assemblages alongside streams both at Neotropical and local scale. This is the first study using modern phylogenetic comparative metrics for covering potential causes of phenotypic and phylogenetic structure of anuran assemblages, and one of the few testing a link between community ecology and the evolutionary biology of acoustic communication to understand the processes mediating species co-occurrence in vertebrates.