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Location of tooth sample collections of common bottlenose dolphins (CBD) and south Australian bottlenose dolphins (SABD). It can be seen that the CBD strandings occur on beaches open to offshore waters, whereas the SABD mainly strands in either Port Phillip Bay or the Gippsland Lakes. doi:10.1371/journal.pone.0016457.g001
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Understanding the foraging ecology and diet of animals can play a crucial role in conservation of a species. This is particularly true where species are cryptic and coexist in environments where observing feeding behaviour directly is difficult. Here we present the first information on the foraging ecology of a recently identified species of dolphi...
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Context 1
... SABD is commonly found in coastal areas of Port Phillip Bay and the Gippsland Lakes whereas the CBD is rarely seen in these coastal areas and more regularly observed in the offshore areas of Bass Strait. These observations of dolphin species sightings are also supported by the locations of strandings of both of these species (Figure 1) with the SABD commonly stranding in inshore coastal waters of Port Phillip Bay and the Gippsland Lakes, whereas the CBD regularly strands on beaches exposed to offshore waters. Therefore, it is hypothesised that SABD are more reliant on coastal prey sources than CBD which may rely more heavily on offshore food sources. ...
Context 2
... salinity of the Lakes also varies seasonally, being influenced by salt water entering from Bass Strait and variability in fresh water inputs from river inflows [47]. Both Port Phillip Bay and the Gippsland Lakes are connected to the offshore environment of Bass Strait located between Victoria and Tasmania, Australia (Figure 1). These environmental differences are likely to result in variation in basal resource availability and consequently, in the dominant fish species in the two waterways. ...
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Citations
... King George whiting, are documented prey items of Burrunan dolphins Owen et al., 2011). There is Bay, the highest proportion of snapper was found between 7 and 18 m, and the King George whiting was found within 2-10 m (Jenkins et al., 2020). ...
... However, it is also possible, given the close proximity of this region to Bass Strait, Burrunan dolphins may travel outside of PPB in search of resources. Stable isotope analysis conducted byOwen et al. (2011) found that the PPB population was 4.5% higher in δ 15 N than the average signature of potential prey items within PPB. This suggests that the PPB population have additional unidentified prey resources that have a higher trophic level than that of the prey items sampled. ...
Bottlenose dolphin ( Tursiops ) populations, also described as the Burrunan dolphins, consist of a resident population of approximately 150 individuals in Port Phillip Bay (PPB), Victoria. Previous reports indicate distribution across a small southern region of PPB; however, little is known about their full distribution patterns across the entire PPB region. Here, we investigate the spatiotemporal distribution of the Burrunan dolphins across four zones representative of PPB benthic habitats and bathymetry to gain a better understanding of the potential drivers of the population's habitat use. Port Phillip Bay, Victoria, Australia. One hundred and twenty‐nine boat‐based surveys were undertaken between March 2015 and August 2021, encompassing 181 sightings. Generalised linear models (GLMs) were used to investigate annual, seasonal and zonal variation. We found no variation in sighting frequencies between years. Austral summer and winter had a significantly higher sighting frequency than autumn. We found that Burrunan dolphins utilise the entire bay, further extending the species range, and show a significantly higher number of sightings in the southern zone than in any other zones. Overlaying dolphin sightings with known oceanographic characteristics within PPB, we found bathymetry and benthic habitats were potential drivers for the Burrunan dolphins distribution and habitat use within the bay, with the dolphins significantly favouring the 5–10 and 10–15 m contour depths. These results show a more widespread distribution across the bay than previously documented. We recommend expansion of the current marine protected areas in the north and south of the bay. This study has increased our understanding of the vital habitat for the Burrunan dolphin populations. By providing evidence‐based conservation recommendations, we hope to improve and contribute to future research, conservation management plans and effective marine protected areas across PPB for the resident Burrunan dolphin population.
... While stomach content analysis is a valuable tool in studies of diet composition, it can be biased due to inherent problems in the sampling regime and prey identification (Pierce & Boyle, 1991;Santos et al., 2001). Stomach contents can only be collected from dead stranded animals, which limits sampling opportunities (Barros et al., 2004;Matley et al., 2015), and stranded animals may have been engaged in abnormal feeding behavior before stranding due to illness (Owen et al., 2011); misrepresenting the actual diet of a healthy animal. Stomach contents are also biased toward hard parts such as otoliths and beaks, which are resistant to digestion, and may cause overestimation of the importance of particular prey such as cephalopods (Bowen & Iverson, 2013). ...
Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning in space and time. Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range in northern Australian waters. We compared stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014– 2015. Both species had similar δ13C and δ15N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial di- etary overlap, and rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ15N value than humpback dolphins, indi- cating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ13C range suggesting they may forage on a wider range of habi- tats. Overall, results suggest that subtle differences in habitat use and prey selection are likely the principal resource partitioning mechanisms enabling the coexistence of Australian snubfin and humpback dolphins.
... Although stomach contents analysis has been used to investigate ecological questions in cetaceans in the past, it is not always a viable option on stranded animals, due to differences in digestion rates of prey species, and carcass deterioration [114][115][116]. Both stable isotope and fatty acid analysis have been previously used to investigate trophic interactions [113], diet [117,118], and resource partitioning [119,120] in cetacean species. Should there be dietary specialisation within species, dietary overlap, or resource partitioning, between co-occurring species, this should be reflected in stable isotope signatures taken from body tissues during necropsy examinations. ...
Climate change is predicted to have profound consequences for marine ecosystems. Due to the growing political and social drive to address its impacts, monitoring and mitigating climate change is a priority in marine policy in the UK. Cetaceans have been proposed as informative sentinel species for monitoring ocean health. Here, strandings data from four UK cetacean species were assessed for their use as a tool to aid policy makers monitoring climate change in marine environments. Data on stranded cetaceans were collected from 1990 to 2018 and differences in the proportions of stranded cold water adapted and warm water adapted species assessed using Generalised Linear Models (GLM), with 6-year periods and four regions of the UK included as explanatory variables. This modelling approach showed an increase in the proportion of stranded warm water adapted species over time across the UK and that differences in proportion of strandings between cold water and warm water adapted species can be detected between regions and 6-year periods, chosen as metrics to coordinate with reporting cycles for policy assessment needs. As such, these results show the potential for utilising strandings data to identify changing oceanic trends at the appropriate spatial and temporal scales for policy reporting in the UK. However, development of these analyses with a more detailed examination of
... Niche partitioning should allow cryptic species to escape competitive exclusion, for example via spatial partitioning as shown in butterflies or fig wasps (Vodȃ et al., 2015;Darwell & Cook, 2017) or trophic differentiation as shown for bats (Siemers et al., 2011) or dolphins (Owen et al., 2011). Ca. femoratus PAT and PS have different climate niches, but still often occur in sympatry . ...
1. The potential for competition is highest among species in close association. Despite net benefits for both parties, mutualisms can involve costs, including food competition. This might be true for the two neotropical ants Camponotus femoratus and Crematogaster levior, which share the same nest in a presumably mutualistic association (parabiosis).
2. While each nest involves one Crematogaster and one Camponotus partner, both taxa were recently found to comprise two cryptic species that show no partner preferences and seem ecologically similar. Since these cryptic species often occur in close sympatry, they might need to partition their niches to avoid competitive exclusion.
3. Here, we investigated first, is there interference competition between parabiotic Camponotus and Crematogaster, and do they prefer different food sources under competition? And second, is there trophic niche partitioning between the cryptic species of either genus?
4. Using cafeteria experiments, neutral lipid fatty acid and stable isotope analyses, we found evidence for interference competition, but also trophic niche partitioning between Camponotus and Crematogaster. Both preferred protein‐ and carbohydrate‐rich baits, but at protein‐rich baits Ca. femoratus displaced Cr. levior over time, suggesting a potential discovery‐dominance trade‐off between parabiotic partners. Only limited evidence was found for trophic differentiation between the cryptic species of each genus.
5. Although we cannot exclude differentiation in other niche dimensions, we argue that neutral dynamics might mediate the coexistence of cryptic species. This model system is highly suitable for further studies of the maintenance of species diversity and the role of mutualisms in promoting species coexistence.
... In the present study, we examined the stomach content recovered from humpback dolphins that stranded in the PRD region between 2003 and 2017. As stomach contents represent a snapshot of individual feeding habits and findings from an individual stomach may be biased towards the prey available at its stranding site/region (Ambrose et al. 2013), spatial factors and representatively wide geographic range have to be considered, especially when studying highly mobile animals (Owen et al. 2011). In the PRD, to be representative the geographic range has to include not only diverse environmental features but also a spatial pattern (or gradient) of anthropogenic impacts, as they likely cause varying degree of stress acting on the marine biota (Sanderson et al. 2010;Green et al. 2016;Karczmarski et al. 2016). ...
The Pearl River Delta (PRD) region on the southeast coast of China has long been known as a highly productive fishing ground. Since the late 1980s, fishing pressure in the PRD has been intense, which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region, such as the Indo-Pacific humpback dolphin (Sousa chinensis). In this study, we examined 54 stomachs with food remains, collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017. The 6043 identified prey items represent 62 teleost taxa, primarily small estuarine fish, but also larger reef fish. The dolphins appear to be opportunistic foragers, hunting across the water-column, with preference for shoaling and meaty fishes (e.g. Chrysochir aureus IRI% = 38.6%, Johnius belangerii IRI% = 23.1%, Mugil cephalus IRI% = 14.0%). Our findings suggest a dietary shift in recent years, from primarily demersal (as previously reported) to greater intake of neritic and pelagic fish. Dolphin foraging group size has decreased in recent years, which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs. We suggest that these are indicators of declining food resources. Faced with a shortage of preferred prey, humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake, while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging.
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... Furthermore, the investigation of habitat preferences and trophic ecology of an individual is very important for understanding the roles and niches occupied by it (e.g. Das et al., 2000;Gross et al., 2009;Bisi et al., 2013;Santos-Carvalho, 2015), which may in turn help with conservation strategies for populations (Owen et al., 2011). In this sense, a coupled approach using photo-identification and SIA was applied to: (1) investigate the occurrence and movements of bottlenose dolphins along the south-eastern Brazilian coast; (2) evaluate their habitat use and the trophic ecology of the species in the region; (3) compare movements and isotopic signatures calculated here with previous studies. ...
Bottlenose dolphins ( Tursiops truncatus ) have been surveyed for at least two decades on the southern Brazilian coast. However, little is known about their distribution and habitat use in lower latitudes of the South-western Atlantic Ocean. Aiming to study the movements and distribution of the species along the south-eastern Brazilian coast, we made a comparison of photo-identified individuals of the species catalogued in 21 cruises conducted between 2012 and 2015. Additionally, we performed stable isotope analyses of carbon and nitrogen in skin samples (N = 35) to provide some insights of dolphin habitat use and trophic ecology through comparisons among individuals of distinct surveyed sectors (northern and southern) and sex. A total of 177 individuals were identified. Re-sightings (N = 24) occurred at intervals from 82 to 979 days at distances from 7 to 179 km. No individual was sighted in both sectors, suggesting spatial segregation. Isotopic comparisons showed no significant differences in carbon and nitrogen signatures between distinct sectors. However, ecological divergences were found when we divided the samples by gender. Wider isotopic niches were found for the northern bottlenose dolphins vs the southern ones, which could be related to temporal and spatial variation in the availability of resources, as well as possible differences in the home ranges of males and females in each region. This study represents a preliminary evaluation of ecological aspects of bottlenose dolphins along the Brazilian south-eastern coast, however, long-term studies on the feeding ecology and habitat use of this species are important to further improve our knowledge.
... Usually it is assumed that niche partitioning allows cryptic species to escape competitive exclusion, e.g. spatial partitioning as shown in butterflies or fig wasps (Vodă et al. 2015;Darwell & Cook 2017) or very different trophic niches as shown for bats (Siemers et al. 2011) and dolphins (Owen, Charlton-Robb & Thompson 2011). In Ca. femoratus, we found evidence for climatic segregation between the cryptic species although both still occur sympatrically at many sites (Hartke, Sprenger et al. 2019, Chapter 1). ...
Species interactions such as competition, antagonism and mutualism are thought to promote diversification in phenotypic traits and thus significantly contribute to species diversity on Earth. Cuticular hydrocarbons (CHCs) are the major components of the waxy layer covering basically all terrestrial arthropods. Most importantly they protect insects from desiccation and act as agents of chemical communication. The communication functions of CHCs are especially important in social insects, such as ants, bees, wasps or termites. Amongst other functions, ants use CHC profiles to identify mutualistic partner species. A special form of such a mutualism is parabiosis, i.e. two ant species mutualistically sharing the same nest. In this thesis, I investigate the causes and consequences for the divergence of CHC profiles in the parabiotic ant species Crematogaster levior and Camponotus femoratus from the South American rainforest. In Chapter 1, I elucidate the species status of chemically diverged morphs of the ants of both genera mentioned above and discuss which role CHCs could have mediating speciation. I conclusively demonstrate that both, Cr. levior and Ca. femoratus, in fact consist of two cryptic species that, despite only slight morphological differences, strongly differ in their CHC profiles and their genetic background. By in detail investigating CHC differences within and between the cryptic species, I identify several ultimate causes for variation of the CHC profiles in Chapter 2. Especially the parabiotic lifestyle led to strong changes such as elongations of the carbon backbone of the CHCs, in both cryptic species of Ca. femoratus, but only one of Cr. levior. Although the cryptic species are closely related, they show vastly different CHC profiles, which is why I further investigated if gene expression differences at the site of CHC biosynthesis might explain this in Chapter 3. In this chapter, I identify several candidate genes and their expression patterns as proximate causes for the CHC variation. In many cases I am able to show that the gene expression differences between the cryptic species are mirrored in the differences observed in their CHC profiles. The strong differences in CHC profiles are likely to have consequences for nestmate recognition and aggression behavior, which is why I investigated recognition within and between the cryptic species of Cr. levior in Chapter 4, trying to identify which substances or structural CHC classes are involved. In line with the hypothesis that elongations of the carbon backbone of CHCs make the molecules harder to perceive, I found that CHC extracts of the shorter-chained Cr. levior species were probably more perceivable and thus treated more aggressively. In Chapter 5, I examine if the species divergence was accompanied by trophic niche partitioning a) between the mutualistic partners and b) between the cryptic species of Cr. levior and Ca. femoratus. Here, the results imply that competition between the mutualists is mediated by a discovery- dominance trade-off and differences in the trophic niche. The differences between the cryptic species, however, were very subtle suggesting that there is either niche differentiation in dimensions I did not investigate so far or that these cryptic species might be an example for ‘neutral species’. Finally, in Chapter 6, I provide an overview on the levels and magnitude of variation in CHC profiles in ants, but also other insects. By reviewing up-to-date literature, I provide detailed insights into sources of fixed and plastic variation on the levels of individuals, social insect colonies, populations and species. Furthermore, I discuss which factors may lead to adaptive CHC changes and how these could be constraint by biosynthetical and biophysical mechanisms. In conclusion, this thesis unravels the existence of cryptic species using integrative taxonomy, provides important insights into the complexity of selection pressures shaping the evolution of CHC profiles and identifies several candidate genes that could be involved in divergence of such profiles. The divergence in CHC profiles could play an important role in mediating speciation. However, it is yet unclear if chemical differences mediated mate choice and led to prezygotic reproductive isolation or if the CHC profiles diverged through reinforcement after speciation. While CHC divergence enabling assortative mating would allow speciation even in sympatry, allopatric populations might diverge through isolation-by-distance, genetic drift or local adaptation reinforcing CHC differences. Furthermore, this thesis identifies the cryptic species of parabiotic ants as an interesting model system to examine how ecologically similar species might avoid competitive exclusion and potentially for the investigation of ‘neutral processes’ mediating species coexistence in tropical ecosystems.
... Using generalized affiliation indices (Whitehead and James 2015), social network techniques, and genetic relatedness analyses, we investigated the social structure of southern Australian bottlenose dolphins in Coffin Bay, South Australia. The southern Australian bottlenose dolphin, or Burrunan dolphin (Tursiops australis), was described as a new species based on genetic, morphological, and stable isotope data Charlton-Robb et al. 2011;Owen et al. 2011). Their taxonomic identity however is still contentious (Perrin et al. 2013; Committee on Taxonomy 2018; IWC Report of the Sub-Comitee on Small Cetaceans 2018), and thus, we refer to them here as southern Australian bottlenose dolphins (Tursiops cf. ...
Social relationships represent an adaptive behavioral strategy that can provide fitness benefits to individuals. Within mammalian societies , delphinids are known to form diverse grouping patterns and show a variety of social systems. However, how ecological and intrinsic factors have shaped the evolution of such diverse societies is still not well understood. In this study, we used photo-identification data and biopsy samples collected between March 2013 and October 2015 in Coffin Bay, a heterogeneous environment in South Australia, to investigate the social structure of southern Australian bottlenose dolphins (Tursiops cf. australis). Based on the data from 657 groups of dolphins, we used generalized affiliation indices, and applied social network and modularity methods to study affiliation patterns among individuals and investigate the potential presence of social communities within the population. In addition, we investigated genetic relatedness and kinship relationships within and between the communities identified. Modularity analysis revealed that the Coffin Bay population is structured into 2 similar sized, mixed-sex communities which differed in ranging patterns, affiliation levels and network metrics. Lagged association rates also indicated that nonrandom affiliations persisted over the study period. The genetic analyses suggested that there was higher relatedness, and a higher proportion of inferred full-sibs and half-sibs, within than between communities. We propose that differences in environmental conditions between the bays and kinship relationships are important factors contributing to the delineation and maintenance of this social structure.
... Currently two species, T. truncatus, and T. aduncus are widely accepted based on morphological and genetic evidence, and a third (T. australis) has been recently proposed (Wang et al. 1999;Charlton-Robb et al. 2011;Owen et al. 2011;Moura et al. 2013). However, molecular genetic evidence also shows reciprocal monophyly for the South African and Asian "aduncus" forms (Natoli et al. 2004;Moura et al. 2013) and supports other proposed taxonomic units, such as the named subspecies in the Black Sea, T. truncatus ponticus (Natoli et al. 2005;Viaud-Martínez et al. 2008). ...
For highly mobile species that nevertheless show fine-scale patterns of population genetic structure, the relevant evolutionary mechanisms determining structure remain poorly understood. The bottlenose dolphin (Tursiops truncatus) is one such species, exhibiting complex patterns of genetic structure associated with local habitat dependence in various geographic regions. Here we studied bottlenose dolphin populations in the Gulf of California and Pacific Ocean off Baja California where habitat is highly structured to test associations between ecology, habitat dependence and genetic differentiation. We investigated population structure at a fine geographic scale using both stable isotope analysis (to assess feeding ecology) and molecular genetic markers (to assess population structure). Our results show that there are at least two factors affecting population structure for both genetics and feeding ecology (as indicated by stable isotope profiles). On the one hand there is a signal for the differentiation of individuals by ecotype, one foraging more offshore than the other. At the same time, there is differentiation between the Gulf of California and the west coast of Baja California, meaning that for example, nearshore ecotypes were both genetically and isotopically differentiated either side of the peninsula. We discuss these data in the context of similar studies showing fine-scale population structure for delphinid species in coastal waters, and consider possible evolutionary mechanisms.
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... The role of resource utilisation in the distribution of sympatric species of H. azteca amphipods remains to be explored. Hyalella azteca species could occupy different feeding niches depending on the interaction between their nutritive requirements and competition for resources, as reported for other cryptic species complex (Owen, Charlton-Robb, & Thompson, 2011;Siemers, Greif, Borissov, Voigt-Heucke, & Voigt, 2011) or for non-cryptic species of the genus Hyalella (Castiglioni & Buckup, 2008). It has also been proposed that some H. azteca species could feed primarily on foods with low nutritive value as long as these foods can offer them a refuge against predators (Dionne, 2009). ...
1. Ecological differences among species are usually associated with phenotypic differences that
enable species to lessen interspecific competition. Many cryptic species co-occur in
communities, thus raising the question of their ecological equivalency. In the case of freshwater
amphipods from the Hyalella azteca cryptic species complex, both ecological differences and
overlaps have been reported among species that co-occur in lakes. Since lakes are
heterogeneous habitats that vary in space and time, it is possible that species minimize
interspecific competition by occupying different trophic niches.
2. We tested the hypothesis that amphipod species from the H. azteca complex co-occur by
feeding on different food resources in the littoral zone of boreal lakes. We compared the stable
isotopes ratios (δ 13 C and δ 15 N) of amphipods from different species, and reconstructed their
diets using mixing models.
3. We showed that H. azteca amphipods from different species had isotopic compositions and
habitat uses that greatly overlapped. Differences in isotopic composition often occurred, but
they were also observed for amphipods of the same species sampled at different depths. This
suggests that H. azteca amphipods fed mainly on resources that were available at the site where
they occurred rather than distributed according to the occurrence of a specific resource.
4. The overlap in diets suggests that H. azteca amphipods had overlapping trophic niches.
Therefore, niche partitioning for food resources was not a process explaining the co-occurrence
of these species within these lakes.
5. Competition for food resources was not likely an important mechanism to explain
H. azteca species assemblages in communities. Each H. azteca species apparently fed on food
items that were abundant in the littoral zone of lakes, meaning that competition for food might
be avoided most of the time. If food scarcity ever happens, the scarcity is probably too short to
allow the exclusion of one amphipod species by competitive exclusion because of the low
differences in fitness between the species, allowing Hyalella cryptic species to co-occur during
the open-water season. Neutral mechanisms and ecological drift might also be important to
explain their community dynamics.
