Movement enables mobile organisms to respond to local environmental conditions and is driven by a combination of external and internal factors operating at multiple scales. Here, we explored how ...resource distribution interacted with the internal state of organisms to drive patterns of movement. Specifically, we tracked snail movements on experimental landscapes where resource (algal biofilm) distribution varied from 0 to 100% coverage and quantified how that movement changed over a 24 h period. Resource distribution strongly affected snail movement. Trajectories were tortuous (i.e. Brownian-like) within resource patches but straighter (i.e. Lévy) in resource-free (bare) patches. The average snail speed was slower in resource patches, where snails spent most of their time. Different patterns of movement between resource and bare patches explained movement at larger spatial scales; movement was ballistic-like Lévy in resource-free landscapes, Lévy in landscapes with intermediate resource coverage and approximated Brownian in landscapes covered in resources. Our temporal analysis revealed that movement patterns changed predictably for snails that satiated their hunger and then performed other behaviours. These changes in movement patterns through time were similar across all treatments that contained resources. Thus, external and internal factors interacted to shape the inherently flexible movement of these snails.
The speed and maneuverability of organisms are central to their fitness, determining the strength and outcome of many species interactions that drive population and community-level processes. While ...locomotion is influenced by many internal and external factors, body size and temperature are two key factors governing organismal locomotion. Biologists have been measuring locomotor performance, particularly maximum speed, for over a century. Studies have tended to focus on single species or groups of species that are either phylogenetically related, functionally similar, or use the same habitat. Few studies compare locomotor performance across a diverse range of taxa or locomotor modes, very few have incorporated locomotor traits other than maximum speed, and the data are not accessible in a single database with standardized units. Here, we present a data set we compiled from the literature that contains 2,951 measurements of locomotor performance for five traits (exploratory speed, maximum speed, maximum acceleration, minimum powered turn radius, and maximum angular speed) that are important in the daily lives of many organisms. This represents the most diverse and comprehensive database on animal locomotion yet published and includes 884 species spanning 23 orders of magnitude of body size. Together with body size (mass and length) and temperature (body and ambient), we also provide data on trophic group and habitat (aerial, terrestrial, aquatic). In publishing our data set, we hope to encourage others to contribute to a continued effort to build this locomotion database and to analyze these data for underlying patterns. Interspecific analyses can help elucidate how organismal locomotion varies with important morphological and physiological traits and environmental conditions, revealing generalities and deviations in organismal locomotion. Additionally, intraspecific analyses, which are possible for a number of species in our data set, can help corroborate these patterns and deviations and explore potential mechanisms that could underlie these patterns. Insights from these analyses should uncover drivers of locomotor performance and contribute to an understanding about how locomotion shapes ecological processes across scales. There are no copyright or proprietary restrictions, except this data paper should be cited when data are used for publication. In addition, we would appreciate hearing for which research projects or teaching exercises these data are used.
Intra-population niche differences in generalist foragers have captured the interest of ecologists, because such individuality can have important ecological and evolutionary implications. Few ...researchers have investigated how these differences affect the relationships among ecologically similar, sympatric species. Using stable isotopes, stomach contents, morphology and habitat preference, we examined niche partitioning within a group of five anurans and determined whether variation within species could facilitate resource partitioning. Species partitioned their niches by trophic level and by foraging habitat. However, there was considerable intraspecific variation in trophic level, with larger individuals generally feeding at higher trophic levels. For species at intermediate trophic levels, smaller individuals overlapped in trophic level with individuals of smaller species and larger individuals overlapped with the smallest individuals from larger species. Species varied in carbon isotopes; species with enriched carbon isotope ratios foraged farther from ponds, whereas species with depleted carbon isotope values foraged closer to ponds. Our study shows that these species partition their niches by feeding at different trophic levels and foraging at different distances from ponds. The intraspecific variation in trophic level decreased the number of individuals from each species that overlapped in trophic level with individuals from other species, which can facilitate species coexistence.
The allometry of locomotion Cloyed, Carl S.; Grady, John M.; Savage, Van M. ...
Ecology (Durham),
July 2021, Letnik:
102, Številka:
7
Journal Article
Recenzirano
Organismal locomotion mediates ecological interactions and shapes community dynamics. Locomotion is constrained by intrinsic and environmental factors and integrating these factors should clarify how ...locomotion affects ecology across scales. We extended general theory based on metabolic scaling and biomechanics to predict the scaling of five locomotor performance traits: routine speed, maximum speed, maximum acceleration, minimum powered turn radius, and angular speed. To test these predictions, we used phylogenetically informed analyses of a new database with 884 species and found support for our quantitative predictions. Larger organisms were faster but less maneuverable than smaller organisms. Routine and maximum speeds scaled with body mass to 0.20 and 0.17 powers, respectively, and plateaued at higher body masses, especially for maximum speed. Acceleration was unaffected by body mass. Minimum turn radius scaled to a 0.19 power, and the 95% CI included our theoretical prediction, as we predicted. Maximum angular speed scaled higher than predicted but in the same direction. We observed universal scaling among locomotor modes for routine and maximum speeds but the intercepts varied; flying organisms were faster than those that swam or ran. Acceleration was independent of size in flying and aquatic taxa but decreased with body mass in land animals, possibly due to the risk of injury large, terrestrial organisms face at high speeds and accelerations. Terrestrial mammals inhabiting structurally simple habitats tended to be faster than those in complex habitats. Despite effects of body size, locomotor mode, and habitat complexity, universal scaling of locomotory performance reveals the general ways organisms move across Earth’s complex environments.
Lipid‐rich animal tissues have low δ13C values, which can lead to inaccurate ecological inferences. Chemical lipid extraction (LE) or correction models account for this depletion, but the need for LE ...or correction is tissue‐ and species‐specific. Also, LE can alter δ15N values, increasing labour and costs because bulk samples must be analysed for δ15N values separately.
We studied the effects of LE on δ13C and δ15N values in liver, muscle and skin of common bottlenose dolphins Tursiops truncatus and West Indian manatees Trichechus manatus, two ecologically important species that occupy different trophic levels. We fit lipid‐correction models to each species. We also performed a meta‐analysis to more broadly determine the effects of LE across taxa, tissues and trophic groups (carnivores, omnivores and herbivores) and to fit lipid‐correction models to different taxonomic and trophic groups.
Lipid extraction increased the δ13C values in dolphin tissues but had little effect on manatee tissues and no effect on the δ15N values in either species. A mass balance lipid‐correction model best fit the data from all dolphin tissues, and a linear model best fit data for manatee liver while null models best fit data from manatee muscle and skin. Across 128 terrestrial and aquatic species, the effects of LE varied among tissues and were lower for herbivores compared to carnivores. The best‐fitting lipid‐correction models varied among tissue, taxa and trophic groups. Finally, the δ15N values from muscle and liver were affected by LE.
Our results strengthen the growing body of evidence that the need for LE is tissue‐ and species‐specific, without a reliable C:N ratio predictive threshold. The prediction errors of lipid‐correction models generally decreased with taxonomic and trophic specificity. The smaller effects of LE in herbivores may be due to differences in diet composition or the physiology of lipid synthesis in members of this trophic group. These results suggest that researchers should use the most species‐, tissue‐ and trophic group‐specific information on LE available and, if not available, perform LE on a subset of samples prior to analysis to determine effects.
Niche partitioning is an important mechanism for allowing ecologically similar species to coexist, contributing to biodiversity and the functioning of ecological communities. Species partition niches ...by taking advantage of environmental heterogeneity. However, niche partitioning and species coexistence investigations often do not include intraspecific variation or individual differences like sex and body size even though these factors can have important ecological consequences. Such intrapopulation factors can reduce the number of individuals among species that overlap in resource use and potentially facilitate coexistence. Using stable isotopes (δ
13
C and δ
15
N), we quantified dietary differences among three ecologically similar, sympatric watersnake species:
Nerodia erythrogaster
,
N. rhombifer
and
N. sipedon
. Additionally for each species, we determined intraspecific dietary patterns and determined how those within-species patterns may contribute to dietary niche partitioning among species.
Nerodia erythrogaster
fed more on terrestrial prey, while
N. rhombifer
fed at higher trophic levels. Females across species fed at higher trophic levels than did males, and isotopic variance differed between the sexes in
N. sipedon
. Larger watersnakes foraged at higher trophic levels and fed more on terrestrial prey. Each watersnake species had a distinct diet that overlapped to some degree with the other species’ diets, but these diets varied both between sexes and among size groups within species. This inter- and intraspecific dietary variation can facilitate species coexistence by reducing the number of individuals from all species that use the same resources. Intraspecific variation can add important and nuanced layers to the evolution of species coexistence, and research on interspecific niche relationships needs to increasingly consider the effects of these intraspecific variations.
Mobile, apex predators are commonly assumed to stabilize food webs through trophic coupling across spatially distinct habitats. The assumption that trophic coupling is common remains largely ...untested, despite evidence that individual behaviors might limit trophic coupling. We used stable isotope data from common bottlenose dolphins across the Gulf of Mexico to determine if these apex predators coupled estuarine and adjacent, nearshore marine habitats. δ
C values differed among the sites, likely driven by environmental factors that varied at each site, such as freshwater input and seagrass cover. Within most sites, δ
C values differed such that dolphins sampled in the upper reaches of embayments had values indicative of estuarine habitats while those sampled outside or in lower reaches of embayments had values indicative of marine habitats. δ
N values were more similar among and within sites than δ
C values. Data from multiple tissues within individuals corroborated that most dolphins consistently used a narrow range of habitats but fed at similar trophic levels in estuarine and marine habitats. Because these dolphins exhibited individual habitat specialization, they likely do not contribute to trophic coupling between estuarine and adjacent marine habitats at a regional scale, suggesting that not all mobile, apex predators trophically couple adjacent habitats.
Ecological studies of global warming impacts have many constraints. Organisms are often exposed to higher temperatures for short periods of time, probably underestimating their ability to acclimate ...or adapt relative to slower but real rates of warming. Many studies also focus on a limited number of traits and miss the multifaceted effects that warming may have on organisms, from physiology to behaviour. Organisms exhibit different movement traits, some of which are primarily driven by metabolic processes and others by decision‐making, which should influence the extent to which temperature affects them.
We collected snails from streams that have been differentially heated by geothermal activity for decades to determine how long‐term exposure to different temperatures affected their metabolism and movement. Additionally, we collected snails from a cold stream (5°C) and measured their metabolism and movement at higher temperatures (short‐term exposure). We used respirometry to measure metabolic rates and automated in situ image‐based tracking to quantify several movement traits from 5 to 21°C.
Long‐term exposure to higher temperatures resulted in a greater thermal sensitivity of metabolic rate compared to snails exposed for short durations, highlighting the need for caution when conducting acute temperature exposures in global warming research. Average speed, which is largely driven by metabolism, also increased more with temperature for long‐term exposure compared to short‐term exposure. Movement traits we interpret as more decision‐based, such as time spent moving and trajectory shape, were less affected by temperature. Step length increased and step angle decreased at higher temperatures for both long‐ and short‐term exposure, resulting in overall straighter trajectories. The power‐law exponent of the step length distributions and fractal dimension of trajectories were independent of temperature, however, suggesting that snails retained the same movement strategy.
The observed changes in snail movement at higher temperatures should lead to higher encounter rates and more efficient searching, providing a behavioural mechanism for stronger plant–herbivore interactions in warmer environments. Our research is among the first to show that temperature has contrasting effects on different movement traits, which may be determined by the metabolic contribution to those behaviours.
Metabolic rate increased more for freshwater snails exposed to higher temperatures for long periods compared to those exposed for short periods. This resulted in higher average speeds and straighter trajectories in warmer streams, providing a potential mechanism for the increased strength of plant–herbivore interactions that occurs in warm environments.
Individual generalist predators often have more specialized diets than their populations do. Individual specialization (IS) is influenced by ecological opportunity, intraspecific competition, and ...interspecific competition, although the effects of these parameters are inconsistent across studies. We investigated IS in five species of frogs and toads, Anaxyrus americanus, A. fowleri, Lithobates catesbeianus, L. clamitans, and L. sphenocephalus. We used the natural history and ecology of each species to predict which parameters would influence IS. Our predictions were supported for some species but not others. We predicted IS would be positively influenced by resource diversity in all species, but this prediction held for only three species, with the relationship significant in A. fowleri and L. catesbeianus and marginally significant in A. americanus. We also predicted that interspecific competition would have a negative relationship with IS in L. clamitans because L. catesbeianus is competitively superior to L. clamitans and likely to suppress its foraging options. This prediction was upheld. Finally, we predicted that IS in A. americanus, A. fowleri, and L. clamitans would be influenced by intraspecific competition. However, IS was not influenced by intraspecific competition in any species, a surprising result given that intraspecific competition has traditionally been assumed to be the ecological parameter with the strongest effects on IS. Many previous studies did not simultaneously consider all three ecological parameters, which may have increased the apparent importance of intraspecific competition for IS. Our results revealed that the ecological parameters affected IS differently even across closely related and ecologically similar species, and demonstrated that these differences are sometimes predictable based on natural history. This study also suggests that sympatric ecological speciation based on IS may be rare because the ecological parameters driving IS are inconsistent across species, and the strength of their effects on intraspecific diet variation varies in space.
Stable isotope analysis (SIA) provides ecological data that can be safely and efficiently collected on endangered, threatened, and cryptic species. Marine mammals are an ecologically important group ...for which economical and logistical constraints can make data collection challenging. Stranded marine mammals are often used in research, but the causes of strandings and subsequent tissue decomposition could affect SIA. We conducted a three‐part study to test the validity of using δ13C and δ15N values from tissues of stranded bottlenose dolphins (Tursiops truncatus) and West Indian manatees (Trichechus manatus) for ecological studies. First, we quantified isotopic overlap using ellipses based on 95% of the data to compare isotope values in skin between stranded and live‐captured animals. Second, we compared stable isotope values from liver, skin, and muscle of animals that had stranded and were sampled at different decomposition stages. Third, we experimentally exposed each tissue to environmental conditions and sampled tissues as they decomposed. For both dolphins and manatees, isotopic ellipses from skin of stranded carcasses were similar to live‐captured individuals. Among individuals recovered at different decomposition stages, more advanced decomposition affected δ13C values in dolphin liver and skin but not in manatee tissues and had no effect on δ15N values in any tissue for either species. In the experimental manipulation, decomposition resulted in depleted δ13C values, enriched δ15N values, and increased C:N in liver for both species. Skin and muscle from stranded dolphins and manatees are representative of their corresponding live populations and can be used for SIA with appropriate caution. To facilitate the use of tissues from stranded animals, tissues should be dried or frozen for storage as soon as possible after sampling. We recommend liver from stranded animals only be used for SIA when researchers need tissues with short turnover times and can access fresh samples. Without consideration of decomposition effects on isotope values, ecologists may make inaccurate inferences about habitat use, diet, and community structure. Careful use of SIA on tissues from stranded animals can help researchers provide better quality information for managers and policy makers.
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