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51 results for “ecological specialization”
Ecological specialization, rather than the island effect, explains morphological diversification in an ancient radiation of geckos
Island colonists are often assumed to experience higher levels of phenotypic diversification than continental taxa. However, empirical evidence has uncovered exceptions to this 'island effect'. Here, we tested this pattern using the geckos of the genus Pristurus from continental Arabia and Africa and the Socotra Archipelago. Using a recently published phylogeny and an extensive morphological dataset, we explore the differences in phenotypic evolution between Socotran and continental taxa. Moreover, we reconstructed ancestral habitat occupancy to examine if ecological specialization is correlated with morphological change, comparing phenotypic disparity and trait evolution between habitats. We found a heterogeneous outcome of island colonization. Namely, only one of the three colonization events resulted in a body size increase. However, in general, Socotran species do not present higher levels or rates of morphological diversification than continental groups. Instead, habitat specialization explains better the body size and shape evolution in Pristurus . Particularly, the colonization of ground habitats appears as the main driver of morphological change, producing the highest disparity and evolutionary rates. Additionally, arboreal species show very similar body size and head proportions. These results reveal a determinant role of ecological mechanisms in morphological evolution and corroborate the complexity of ecomorphological dynamics in continent–island systems.
Linking ecological specialization to its macroevolutionary consequences: An example with passerine nest type
<p>A long-standing hypothesis in evolutionary biology is that the evolution of resource specialization can lead to an evolutionary dead end, where specialists have low diversification rates and limited ability to evolve into generalists. In recent years, advances in comparative methods investigating trait-based differences associated with diversification have enabled more robust tests of this idea and have found mixed support. We test the evolutionary dead end hypothesis by estimating net diversification rate differences associated with nest site specialization among 3,224 species of passerine birds. In particular, we test whether the adoption of hole-nesting, a nest site specialization that decreases predation, results in reduced diversification rates relative to nesting outside of holes. Further, we examine whether evolutionary transitions to the specialist hole-nesting state have been more frequent than transitions out of hole-nesting. Using diversification models that accounted for background rate heterogeneity and different extinction rate scenarios, we found that hole-nesting specialization was not associated with diversification rate differences. Furthermore, contrary to the assumption that specialists rarely evolve into generalists, we found that transitions out of hole-nesting occur more frequently than transitions into hole-nesting. These results suggest that interspecific competition may limit adoption of hole-nesting, but that such competition does not result in limited diversification of hole-nesters. In conjunction with other recent studies using robust comparative methods, our results add to growing evidence that evolutionary dead ends are not a typical outcome of resource specialization.</p>
Linking ecological specialization to its macroevolutionary consequences: An example with passerine nest type
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Ecological specialization, rather than the island effect, explains morphological diversification in an ancient radiation of geckos
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Considerable genetic diversity and structure despite narrow endemism and limited ecological specialization in the Hayden's ringlet, Coenonympha haydenii
<p>Understanding the processes that underlie the development of population genetic structure is central to the study of evolution. Patterns of genetic structure can reveal signatures of isolation by distance, barriers to gene flow, or even the genesis of speciation. However, it is unclear how severe range restriction might impact the processes that dominate the development of genetic structure. In narrow endemic species, is population structure likely to be adaptive in nature, or rather the result of genetic drift? In this study, we investigated patterns of genetic diversity and structure in the narrow endemic Hayden's ringlet butterfly. Specifically, we asked to what degree genetic structure in the Hayden's ringlet can be explained by isolation by distance, isolation by resistance (in the form of geographic or ecological barriers to migration between populations), and isolation by environment (in the form of differences in host plant availability and preference). We employed a genotyping-by-sequencing (GBS) approach coupled with host preference assays, Bayesian modeling, and population genomic analyses to answer these questions. Our results suggest that despite their restricted range, levels of genetic diversity in the Hayden's ringlet are comparable to those seen in more widespread butterfly species. Hayden's ringlets showed a strong preference for feeding on grasses relative to sedges, but neither larval preference nor potential host availability at sampling sites correlated with genetic structure. We conclude that geography, in the form of isolation by resistance and simple isolation by distance, was the major driver of contemporary patterns of differentiation in this narrow endemic species.</p>
Do ecological specialization and functional traits explain the abundance–frequency relationship? Arable weeds as a case study
<p>Aim: The abundance-frequency relationship (AFR) is among the most-investigated pattern in biogeography, yet the relative contributions of niche-based processes related to ecological strategies, and of neutral processes related to spatial colonization-extinction dynamics, remains uncertain. Here, we tested the influences of ecological specialization and functional traits on local abundance and regional frequency, to determine the contribution of niche-based processes.</p> <p>Location: France and the UK.</p> <p>Taxon: Vascular plants.</p> <p>Methods: We used two arable weed surveys covering 1544 fields in Western Europe (France, UK), along with functional traits related to resource acquisition, flowering phenology and dispersal. We quantified specialization both to arable habitat and to individual crop types, and performed phylogenetic path analyses to test competing models accounting for direct and indirect relationships between traits, specialization, abundance and frequency. We performed the analyses for all species in each country, as well as for a subset of the most abundant species.</p> <p>Results: Local abundance of weeds increased with their regional frequency, but the relationship became negative or null when considering only the most abundant weeds. Specialization to arable habitat and to individual crop type either had a similar or opposite effect on regional frequency and local abundance explaining these positive and negative relationships, respectively. Regional frequency was not directly explained by any trait but indirectly by resource requirement traits conferring specialization to the arable habitat. Conversely, high local abundance was directly related to low seed mass, high SLA, early and short flowering.</p> <p>Main Conclusions: Direct/indirect effects of functional traits on local abundance/regional frequency, respectively, supports a significant role of niche-based processes in AFR. Neutral spillover dynamics could further explain a direct linkage of abundance and frequency. Similar causal paths and consistent influences of traits on specialization and abundance in the two studied regions suggest genericity of these findings.</p>
Do ecological specialization and functional traits explain the abundance–frequency relationship? Arable weeds as a case study
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Considerable genetic diversity and structure despite narrow endemism and limited ecological specialization in the Hayden's ringlet, Coenonympha haydenii
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Data from: Specialization and niche overlap across spatial scales: revealing ecological factors shaping species richness and coexistence in Australian songbirds
1. Ecological specialization enables the partitioning of resources and thus can facilitate the coexistence of species and promote higher species richness. Specialization and niche partitioning are expected to exert a decisive influence on local spatial scales, while species richness at regional scales should be shaped mostly by historical factors and abiotic conditions. Moreover, specialization is expected to be particularly important in communities that are exceptionally species rich for their environmental conditions. Concurrently, niche overlap in these communities should be minimized to enable species coexistence. 2. We tested these hypotheses by studying specialization-richness relationship and niche overlap in assemblages of 298 species of songbirds (Passeriformes) across Australia. We used local (2-6 ha) to regional (bioregions) spatial scales, and detailed data on habitat, diet, and foraging behaviour (method, substrate, and stratum). 3. We expected the richness-specialization relationship to be particularly strong i) on local spatial scales and ii) in communities exceptionally species rich for given environmental conditions (approximated by moisture and vegetation complexity). We also expected iii) low niche overlap in assemblages with specialized species. 4. Only the third prediction was partly supported. First, while the specialization and species richness were often positively related, the strength and the direction of the relationship changed between traits and across spatial scales. The strength of the specialization-richness relationship was consistently positive only in foraging stratum, and it increased towards smaller spatial scales only in case of habitat and diet. Simultaneously, species in local communities demonstrated high overlap in habitat and diet. Second, we did not find particularly strong specialization-richness relationships in exceptionally species rich communities. Third, we found the expected negative relationship between specialization and overlap in foraging stratum and substrate (in local communities), suggesting that species partition ecological space locally in terms of where they find food. 5. Our expectations were only weakly supported. Specialization on foraging stratum was probably important in facilitating species co-existence. Conversely, although species were often specialized on habitat and diet, high overlap in these traits did not preclude their local coexistence. Overall, specialization and overlap in foraging traits were more important for species coexistence than habitat or diet.
Data from: Behavioral adaptations imply a direct link between ecological specialization and reproductive isolation in a sympatrically diverging ground beetle
Adaptation to a previously unoccupied niche within a single population is one of the most contentious topics in evolutionary biology as it assumes the simultaneous evolution of ecologically selected and preference traits. Here, we demonstrate behavioral adaptation to contrasting hydrological regimes in a sympatric mosaic of Pogonus chalceus beetle populations, and argue that this adaptation may result in nonrandom gene flow. When exposed to experimental inundations, individuals from tidal marshes, which are naturally subjected to frequent but short floods, showed a higher propensity to remain submerged compared to individuals from seasonal marshes that are inundated for several months. This adaptive behavior is expected to decrease the probability that individuals will settle in the alternative habitat, resulting in spatial sorting and reproductive isolation of both ecotypes. Additionally, we show that this difference in behavior is induced by the environmental conditions experienced by the beetles during their nondispersive larval stages. Hence, accidental or forced ovipositioning in the alternative habitat may induce both an increased performance and preference to the natal habitat type. Such plastic traits could play an important role in the most incipient stages of divergence with gene flow.
Data from: Biogeography of scorpions in the Pseudouroctonus minimus complex (Vaejovidae) from south-western North America: implications of ecological specialization for pre-Quaternary diversification
Aim: The aim of this study was to assess the impact of pre-Quaternary tectonics and orogeny relative to that of Pleistocene climate change on diversification within the Pseudouroctonus minimus complex, a group of vaejovid scorpions with stenotopic habitat requirements. Location: South-western North America (United States and Mexico). Methods: Multilocus sequence data (1899 base pairs from two mitochondrial and two nuclear genes) were generated from 65 samples of scorpions in the minimus complex. Phylogeographical structure within the minimus complex was explored using model-based phylogenetic methods and a general mixed Yule coalescent model to identify independent geographical clusters. A time-calibrated multilocus species tree was reconstructed using a multispecies coalescent approach. Ancestral areas were estimated at divergence events across the tree using a probabilistic Bayesian approach. Results: Extensive geographical structure was evident within two well-supported clades. These clades probably diverged over 25 million years ago (Ma), based on estimated mean divergence dates, followed by 14 divergences in the Miocene (25–5 Ma) and 4 divergences in the Pliocene and Pleistocene (< 5 Ma). The ancestral origin of the minimus complex was reconstructed to be across California and the Mexican Highlands. The Chihuahuan Desert was colonized twice from the Mexican Highlands, and one dispersal event occurred from the Mexican Highlands back to California. Main conclusions: Spatial and temporal patterns of evolution in the minimus complex support predictions that stenotopy promoted pre-Quaternary diversification. Miocene and Pliocene geomorphology, perhaps in concert with climate change, induced allopatric divergence across the heterogeneous landscape of south-western North America. Stenotopic scorpions such as the minimus complex provide a model for exploring correlations between Earth history and biological diversification.
Data from: Ecological opportunities and specializations shaped genetic divergence in a highly mobile marine top predator
Environmental conditions can shape genetic and morphological divergence. Release of new habitats during historical environmental changes was a major driver of evolutionary diversification. Here, forces shaping population structure and ecotype differentiation ('pelagic' and 'coastal') of bottlenose dolphins in the North-east Atlantic were investigated using complementary evolutionary and ecological approaches. Inference of population demographic history using approximate Bayesian computation indicated that coastal populations were likely founded by the Atlantic pelagic population after the Last Glacial Maxima probably as a result of newly available coastal ecological niches. Pelagic dolphins from the Atlantic and the Mediterranean Sea likely diverged during a period of high productivity in the Mediterranean Sea. Genetic differentiation between coastal and pelagic ecotypes may be maintained by niche specializations, as indicated by stable isotope and stomach content analyses, and social behaviour. The two ecotypes were only weakly morphologically segregated in contrast to other parts of the World Ocean. This may be linked to weak contrasts between coastal and pelagic habitats and/or a relatively recent divergence. We suggest that ecological opportunity to specialize is a major driver of genetic and morphological divergence. Combining genetic, ecological and morphological approaches is essential to understanding the population structure of mobile and cryptic species.
Data from: Use it or lose it: reproductive implications of ecological specialization in a haematophagous ectoparasite
Using experimentally induced disruptive selection, we tested two hypotheses regarding the evolution of specialization in parasites. The 'trade-off' hypothesis suggests that adaptation to a specific host may come at the expense of a reduced performance when exploiting another host. The alternative 'relaxed selection' hypothesis suggests that the ability to exploit a given host would deteriorate when becoming obsolete. Three replicate populations of a flea Xenopsylla ramesis were maintained on each of two rodent hosts, Meriones crassus and Dipodillus dasyurus, for nine generations. Fleas maintained on a specific host species for a few generations substantially decreased their reproductive performance when transferred to an alternative host species, whereas they generally did not increase their performance on their maintenance host. The results support the 'relaxed selection' hypothesis of the evolution of ecological specialization in haematophagous ectoparasites, while suggesting that trade-offs are unlikely drivers of specialization. Further work is needed to study the extent by which the observed specializations are based on epigenetic or genetic modifications.
Data from: Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators
Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near-top trophic-level marine predators have been little studied in polar regions or with latitude. We quantified the large-scale latitudinal variation of population- and individual-level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both within- and between-individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within-individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large-scale spatial variation in ecological opportunity, suggesting species-specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem.
FIGURE 5 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 5. Plots of the principal component analyses (PCA) and discriminant analyses of principal components (DAPC) for the meristc, mensural, and concatenated data sets illustrating the morphological separation of Tytthoscincus monticolus sp. nov. and T. keciktuek sp. nov.
FIGURE 4 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 4. Maximum Likelihood phylogram depicting the relationships of species within the montane clade of Tytthoscincus and the delimitation of the semi-fossorial and leaf-litter generalist lineages. Black circles denote nodal Bayesian support ± 0.95 and ultrafast bootstrap support ±95, grey circle denotes nodal Bayesian support ± 0.95 only, and the white circle denotes poor Bayesian and ultrafast bootstrap support.
FIGURE 7 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 7. Left: General habitat of Tytthoscincus monticolus sp. nov. and T. keciktuek sp. nov. from the Sekayu region of Hulu Terengganu. Photograph by L. L. Grismer. Upper right: microhabitat at the type locality of T. monticolus sp. nov. near Sungai Bubu, Sekayu, Hulu Terengganu, Terengganu State, Peninsular Malaysia. Photograph by M. Afiq-Shuhaimi. Lower right: microhabitat at the type locality of T. keciktuek sp. nov. from Sungai Peres, Sekayu, Hulu Terengganu, Terengganu State, Peninsular Malaysia. Photograph by M. Aqmal-Naser.
FIGURE 2 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 2. Type localities for Tytthoscincus keciktuek sp. nov. and T. monticolus sp. nov. and their closest relatives T. perhentianensis and Tytthoscincus sp. nov., respectively, in Peninsular Malaysia.
FIGURE 6 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 6. Upper: type specimen (LSUHC 13858) of Tytthoscincus monticolus sp. nov. collected from a hilly area near Sungai Bubu, Sekayu, Hulu Terengganu, Terengganu State, Peninsular Malaysia. Photograph by A. B. Ahmad. Middle: type specimen (LSUHC 13859) of Tytthoscincus keciktuek sp. nov. collected along a small tributary of the Sungai Peres, Sekayu, Hulu Terengganu, Terengganu State, Peninsular Malaysia. Photograph by A. B. Ahmad. Lower: Tytthoscincus butleri (LUSHC 13860) from a new lowland locality at Bukit Mertajam, Penang, Peninsular Malaysia. Photograph by E.S.H. Quah.
FIGURE 3 in Two new Tytthoscincus Linkem, Diesmos, & Brown (Squamata; Scincidae) from Peninsular Malaysia and another case of microsyntopy between ecologically specialized, unrelated, leaf-litter species
FIGURE 3. Generalized illustration of head scale terminology of Tytthoscincus adapted from Grismer et al. (2017a) and Taylor (1935). cs = chinshield; fn = frontonasal; il = infralabial; lo = loreal; m = mental; n = nasal; p = parietal; pf = prefrontal; pm = postmental; po = preorbital; psc = postsuperciliary; psl = postsupralabial; pt = primary temporal; r = rostral; sc = superciliary; sl = supralabial; so = supraorbital; st = secondary temporal; asterisk = subocular; and star = postocular.
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