Seasonal variation in avian diversity and tolerance by migratory forest specialists of the patch-isolation gradient across a fragmented forest system

Forest-habitat loss and fragmentation reduce connectivity, presenting dispersal challenges for many forest-dependent species with deleterious effects on community structure and diversity. It is expected that avian forest specialists are vulnerable to fragmentation, yet seasonal migrants may be more resilient to isolation effects than sedentary specialists. We surveyed bird communities in 138 habitat patches of the critically endangered Indian Ocean Coastal Belt, South Africa, across a range of isolation distances from mainland forests during the breeding and non-breeding seasons. We quantified taxonomic and functional diversity per patch based on species’ traits and performed 26 generalized linear mixed-effects models on the effects of isolation and the amount of habitat in the surrounding matrix on avian trait-diversity measurements. We compared diversity measures between seasons for evidence of resilience to isolation effects for migrants and compared linear regressions of isolation-distance effects to segmented regressions at various isolation distances to explore dispersal limits of sedentary forest specialists. All avian diversity measures were higher during the breeding season. The amount of surrounding habitat was a positive driver of all diversity measures. Isolation-distance effects had the most negative effect during the breeding season, and on sedentary forest specialists, which were unable to disperse across isolation distances > 500 m. Sedentary forest specialists are a conservation priority given (a) their value in perpetuating ecosystem services and (b) their vulnerability to isolation effects. Migratory forest specialists exhibited resilience to the isolation effect during non-breeding; thus, certain specialized niches may be occupied given the vagility of migratory forest specialists.     

Distinct spatiotemporal succession of bacterial generalists and specialists in the lacustrine plastisphere

The assembly processes of generalists and specialists and their driving mechanisms during spatiotemporal succession is a central issue in microbial ecology but a poorly researched subject in the plastisphere. We investigated the composition variation, spatiotemporal succession, and assembly processes of bacterial generalists and specialists in the plastisphere, including non-biodegradable (NBMPs) and biodegradable microplastics (BMPs). Although the composition of generalists and specialists on NBMPs differed from that of BMPs, colonization time mainly mediated the composition variation. The relative abundance of generalists and the relative contribution of species replacement were initially increased and then decreased with colonization time, while the specialists initially decreased and then increased. Besides, the richness differences also affected the composition variation of generalists and specialists in the plastisphere, and the generalists were more susceptible to richness differences than corresponding specialists. Furthermore, the assembly of generalists in the plastisphere was dominated by deterministic processes, while stochastic processes dominated the assembly of specialists. The network stability test showed that the community stability of generalists on NBMPs and BMPs was lower than corresponding specialists. Our results suggested that different ecological assembly processes shaped the spatiotemporal succession of bacterial generalists and specialists in the plastisphere, but were less influenced by polymer types.     

Dynamic trait-niche relationships shape niche partitioning across habitat transformation gradients

Multidimensional approaches examining complex trait-niche relationships are crucial to understand community assembly. This is particularly important across habitat transformation gradients because specialists are progressively substituted by generalists and, despite increasing functional homogenization, in both specialist and generalist communities niche partitioning is apparent. Here, in line with the continuum hypothesis, we expected that divergent trait-niche relationships would arise in passerine assemblages across the natural-to-urban transformation gradient. More specifically, we expected that traits linking form to function would be more important in less transformed habitats, while population density and traits linked to dispersal and dominance would predominate in more transformed habitats. Accordingly, we found that beak length and its interaction with tarsus length correlated significantly with isotopic niches in natural and rural habitats, where specialists predominate. Conversely, body size and aggressiveness only showed significant relationships with isotopic niches with increasing habitat transformation, where generalists prevail. Interestingly, we recorded a mix of these processes in rural habitats, which acted as a frontier between these two domains. Our study is thus important in showing that a complex combination of morphological and behavioral traits determine niche characteristics, and that these relationships are dynamic across habitat transformation gradients.     

Contrasting Patterns of Genetic Differentiation among Blackcaps (Sylvia atricapilla) with Divergent Migratory Orientations in Europe

Migratory divides are thought to facilitate behavioral, ecological, and genetic divergence among populations with different migratory routes. However, it is currently contentious how much genetic divergence is needed to maintain distinct migratory behavior across migratory divides. Here we investigate patterns of neutral genetic differentiation among Blackcap (Sylvia atricapilla) populations with different migratory strategies across Europe. We compare the level of genetic divergence of populations migrating to southwestern (SW) or southeastern (SE) wintering areas with birds wintering in the British Isles following a recently established northwesterly (NW) migration route. The migratory divide between SW and SE wintering areas can be interpreted as a result of a re-colonization process after the last glaciation. Thus we predicted greater levels of genetic differentiation among the SW/SE populations. However, a lack of genetic differentiation was found between SW and SE populations, suggesting that interbreeding likely occurs among Blackcaps with different migratory orientations across a large area; therefore the SW/SE migratory divide can be seen as diffuse, broad band and is, at best, a weak isolating barrier. Conversely, weak, albeit significant genetic differentiation was evident between NW and SW migrants breeding sympatrically in southern Germany, suggesting a stronger isolating mechanism may be acting in this population. Populations located within/near the SW/SE contact zone were the least genetically divergent from NW migrants, confirming NW migrants likely originated from within the contact zone. Significant isolation-by-distance was found among eastern Blackcap populations (i.e. SE migrants), but not among western populations (i.e. NW and SW migrants), revealing different patterns of genetic divergence among Blackcap populations in Europe. We discuss possible explanations for the genetic structure of European Blackcaps and how gene flow influences the persistence of divergent migratory behaviors.     

Community structure of insect herbivores is driven by conservatism,escalation and divergence of defensive traits in Ficus

Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant‐herbivore arms race. We studied the defences and caterpillars associated with 21 sympatric New Guinean figs. Herbivore generalists were concentrated on hosts with low protease and oxidative activity. The distribution of specialists correlated with phylogeny, protease and trichomes. Additionally, highly specialised Asota moths used alkaloid rich plants. The evolution of proteases was conserved, alkaloid diversity has escalated across the studied species, oxidative activity has escalated within one clade, and trichomes have diverged across the phylogeny. Herbivore specificity correlated with their response to host defences: escalating traits largely affected generalists and divergent traits specialists; but the effect of escalating traits on extreme specialists was positive. In turn, the evolution of defences in Ficus can be driven towards both escalation and divergence in individual traits, in combination providing protection against a broad spectrum of herbivores.     

Migratory divides coincide with reproductive barriers across replicated avian hybrid zones above the Tibetan Plateau

Migratory divides are proposed to be catalysts for speciation across a diversity of taxa. However, it is difficult to test the relative contributions of migratory behaviour vs. other divergent traits to reproductive isolation. Comparing hybrid zones with and without migratory divides offers a rare opportunity to directly examine the contribution of divergent migratory behaviour to reproductive barriers. We show that across replicate sampling transects of two pairs of barn swallow (Hirundo rustica) subspecies, strong reproductive isolation coincided with a migratory divide spanning 20 degrees of latitude. A third subspecies pair exhibited no evidence for a migratory divide and hybridised extensively. Within migratory divides, overwintering habitats were associated with assortative mating, implicating a central contribution of divergent migratory behaviour to reproductive barriers. The remarkable geographic coincidence between migratory divides and genetic breaks supports a long‐standing hypothesis that the Tibetan Plateau is a substantial barrier contributing to the diversity of Siberian avifauna.     

Arbuscular mycorrhizal fungal communities in plant roots are not random assemblages

We investigated whether arbuscular mycorrhizal fungal (AMF) communities in plant roots are random subsets of the local taxon pool or whether they reflect the action of certain community assembly rules. We studied AMF small subunit rRNA gene sequence groups in the roots of plant individuals belonging to 11 temperate forest understorey species. Empirical data were compared with null models assuming random association. Distinct fungal species pools were present in young and old successional forest. In both forest types, the richness of plant-AMF associations was lower than expected by chance, indicating a degree of partner selectivity. AMF communities were generally not characteristic of individual plant species, but those associated with ecological groups of plant species - habitat generalists and forest specialists - were nonrandom subsets of the available pool of fungal taxa and differed significantly from each other. Moreover, these AMF communities were the least distinctive in spring, but developed later in the season. Comparison with a global database showed that generalist plants tend to associate with generalist AMF. Thus, the habitat range of the host and a possible interaction with season played a role in the assembly of AMF communities in individual plant root systems.     

Community assembly in temperate forest birds: habitat filtering,interspecific interactions and priority effects

Recent attempts to understand the processes governing community assembly have increasingly focused on patterns of phylogenetic relatedness and functional similarity among co-existing species. Considerations of the species pool, the number and identity of functional traits and the metrics used to identify patterns have come under scrutiny as possible influences on the detection of non-random patterns. Most mechanistic explanations of community assembly based on functional and phylogenetic approaches rely on deterministic explanations, while ignoring the role of stochastic processes and historical contingency, despite the prominent historical role of both types of explanations of species coexistence. We evaluated the phylogenetic and functional structure of 20 temperate forest bird assemblages in northeastern North America. We compared three approaches for characterizing the functional structure of assemblages. Regardless of approach, assemblages were generally no different than expected by chance. In contrast, phylogenetic structures of bird assemblages were overdispersed, clumped or consistent with random assembly depending on the site. Nonetheless, we found little evidence for differences in phylogenetic structure arising as a consequence of the identity of the species pool. We identified a strong relationship between the proportion of residents and phylogenetic relatedness that was unrelated to the species richness of assemblages. Our results suggest that different assembly mechanisms may structure resident and migratory subsets of temperate breeding bird communities. Resident assemblages are likely structured by interspecific interactions and habitat filtering prior to arrival of migrants. In contrast, the composition of migrant assemblages may be a consequence of priority effects in which the presence and abundance of residents and earliest arriving species affect the ability of subsequent migrants to colonize sites. This phenomenon enhances the likelihood of multiple alternative community structures in similar environments.     

Insights on the functional composition of specialist and generalist birds throughout continuous and fragmented forests

A decline in species number often occurs after forest fragmentation and habitat loss, which usually results in the loss of ecological functions and a reduction in functional diversity in the forest fragments. However, it is uncertain whether these lost ecological functions are consistently maintained throughout continuous forests, and so the importance of these functions in continuous forests remains unknown. Point counts were used to assess both the taxonomic and functional diversity of specialist and generalist birds from sampling in a continuous primary forest compared with forest fragments in order to investigate the responses of these groups to forest fragmentation. We also measured alpha and beta diversity. The responses of specialists and generalists were similar when we assessed all bird species but were different when only passerines were considered. When examining passerines we found lower total taxonomic beta diversity for specialists than for generalists in the continuous forest, while taxonomic beta diversity was higher in the fragmented forest and similar between bird groups. However, total functional beta‐diversity values indicated clearly higher trait regularity in continuous forest for specialists and higher trait regularity in fragments for generalists. Specialists showed significantly higher functional alpha diversity in comparison with generalists in the continuous forest, while both groups showed similar values in fragments. In passerines, species richness and alpha functional diversity of both specialist and generalist were explained by forest connectivity; but, only fragment size explained those parameters for specialist passerines. We suggest that considering subsets of the community with high similarity among species, as passerines, provides a better tool for understanding responses to forest fragmentation. Due to the regularity of specialists in continuous forest, their lost could highly affect functionality in forest fragments.     

Ecological traits modulate bird species responses to forest fragmentation in an Amazonian anthropogenic archipelago

Aim

We assessed patterns of avian species loss and the role of morpho‐ecological traits in explaining species vulnerability to forest fragmentation in an anthropogenic island system. We also contrasted observed and detectability‐corrected estimates of island occupancy, which are often used to infer species vulnerability.

Location

Tucuruí Hydroelectric Reservoir, eastern Brazilian Amazonia.

Methods

We surveyed forest birds within 36 islands (3.4–2,551.5 ha) after 22 years of post‐isolation history. We applied species–area relationships to assess differential patterns of species loss among three data sets: all species, forest specialists and habitat generalists. After controlling for phylogenetic non‐independence, we used observed and detectability‐corrected estimates of island occupancy separately to build competing models as a function of species traits. The magnitude of the difference between these estimates of island occupancy was contrasted against species detectability.

Results

The rate of species loss as a function of island area reduction was higher for forest specialists than for habitat generalists. Accounting for the area effect, forest fragmentation did not affect the overall number of species regardless of the data set. Only the interactive model including natural abundance, habitat breadth and geographic range size was strongly supported for both estimates of island occupancy. For 30 species with detection probabilities below 30%, detectability‐corrected estimates were at least tenfold higher than those observed. Conversely, differences between estimates were negligible or non‐existent for all 31 species with detection probabilities exceeding 45.5%.

Main conclusions

Predicted decay of avian species richness induced by forest loss is affected by the degree of habitat specialisation of the species under consideration, and may be unrelated to forest fragmentation per se. Natural abundance was the main predictor of species island occupancy, although habitat breadth and geographic range size also played a role. We caution against using occupancy models for low‐detectability species, because overestimates of island occupancy reduce the power of species‐level predictions of vulnerability.

     

Migratory New World Blackbirds (Icterids) Are More Neophobic than Closely Related Resident Icterids

Environments undergo short-term and long-term changes due to natural or human-induced events. Animals differ in their ability to cope with such changes which can be related to their ecology. Changes in the environment often elicit avoidance reactions (neophobia) which protect animals from dangerous situations but can also inhibit exploration and familiarization with novel situations and thus, learning about new resources. Studies investigating the relationship between a species’ ecology and its neophobia have so far been restricted to comparing only a few species and mainly in captivity. The current study investigated neophobia reactions to experimentally-induced changes in the natural environment of six closely-related blackbird species (Icteridae), including two species represented by two distinct populations. For analyses, neophobic reactions (difference in number of birds feeding and time spent feeding with and without novel objects) were related to several measures of ecological plasticity and the migratory strategy (resident or migratory) of the population. Phylogenetic relationships were incorporated into the analysis. The degree of neophobia was related to migratory strategy with migrants expressing much higher neophobia (fewer birds feeding and for a shorter time with objects present) than residents. Furthermore, neophobia showed a relationship to diet breadth with fewer individuals of diet generalists than specialists returning when objects were present supporting the dangerous niche hypothesis. Residents may have evolved lower neophobia as costs of missing out on opportunities may be higher for residents than migrants as the former are restricted to a smaller area. Lower neophobia allows them approaching changes in the environment (e.g. novel objects) quickly, thereby securing access to resources. Additionally, residents have a greater familiarity with similar situations in the area than migrants and the latter may, therefore, initially stay behind resident species.     

Molecular phylogeny of reed beetles (Col., Chrysomelidae, Donaciinae): the signature of ecological specialization and geographical isolation

The Donaciinae consist of approximately 165 species predominantly occurring in the northern hemisphere. We analysed mitochondrial and nuclear DNA (COI, EF-1alpha) of 46 species to investigate their phylogeny and to discuss general topics in the context of insect herbivory (generalists versus specialists, ecological speciation). Phylogenetic reconstructions from various methodical approaches yielded very similar results. Clades corresponding to the traditional tribes/genera were recovered. Within the genus Donacia, species groups with characteristic host plant preference were identified. Estimated divergence times are discussed on the background of geological events. The origin of the Donaciinae is dated to 75-100 million years before present, after which they quickly diversified into the main groups. An initial split of those groups occurred in the Palaeocene. In the Eocene and Oligocene, major lineages specialized on certain host plants, where they radiated in the Miocene. This radiation was enforced by geographic isolation brought about by the final separation of America and Europe, after which there arose continental lineages within three larger species groups. In their evolution based on ecological specialization with a recently superimposed geographic isolation, the Donaciinae follow a pattern of specialists arising from generalists. Host plant shifts show that such a specialization is not necessarily an 'evolutionary dead-end'.     

Mobility is related to species traits in noctuid moths

1. Mobility is important for the understanding of how species survive in fragmented landscapes and cope with increasing rates of habitat and climate change. However, mobility is a difficult trait to explore and is poorly known in most taxa. Species traits have been studied in relation to range shifts, extinction risks, and responses to habitat area and isolation, and have also been suggested as good estimators of mobility. Here we explore the relation between mobility and species traits in noctuid moths. 2. We sampled noctuid moths by an automatic light‐trap on an island far out in the Baltic Sea. We compared traits of the non‐resident species on the island with traits of a species pool of assumed potential migrants from the Swedish mainland. 3. Mobility was significantly related to adult activity period, length of flight period, and the interaction between host‐plant specificity and distribution area. Widely distributed host‐plant generalists were more mobile than host‐plant specialists with more restricted distribution, and species with an adult activity period in August to September moved to the island to a higher extent than species with an adult activity period in May to July. Our results remained qualitatively robust in additional analyses, after controlling for phylogeny and including all species recorded on the island, except for the trait ‘length of flight period’. 4. Our results highlight the importance of the relation between mobility and species traits. Noctuid moths with certain traits move over longer distances than earlier known. This finding is important to include when predicting range dynamics in fragmented and changing landscapes, and when conservation measures of species are devised.     

Reproductive isolation caused by visual predation on migrants between divergent environments

In theory, natural selection can drive adaptation within species while simultaneously promoting the formation of new species by causing the evolution of reproductive isolation. Cryptic coloration is widespread in nature and is generally considered to be a clear visual example of adaptation. I provide evidence that population divergence in cryptic coloration can also cause reproductive isolation. First, a manipulative field experiment using walking-stick insects demonstrates that the relative survival of different colour-pattern morphs depends on the host-plant species on which they are resting, but only in the presence of avian predation. Second, natural populations adapted to different host plants have diverged in colour-pattern-morph frequencies such that between-host migrants are more likely to be the locally less-cryptic morph than are residents. Collectively, these data indicate that high rates of visual predation on less-cryptic migrants are likely to reduce encounters, and thus interbreeding, between host-associated populations. Comparison with previous estimates of sexual isolation reveals that the contribution of selection against between-host migrants to total premating isolation is as strong as, or stronger than, that of sexual isolation. These findings highlight the potential role of natural selection against migrants between divergent environments in the formation of new species.     

Experimental insights into the importance of ecologically dissimilar bacteria to community assembly along a salinity gradient

The response of local communities to marine–freshwater transitions and the processes that underlie community assembly are unclear, particularly with respect to bacteria that differ in their life strategies. Here, we implemented a transplant experiment where bacterioplankton from three regions of the Baltic Sea with differing salinities (～3, 7 and 28 psu) were exposed to each other's environmental conditions. We found that habitat specialists were more abundant than generalists after exposure to salinity changes, irrespective of their origins. Most specialists that were selected following a salinity change were rare in the starting communities. Selection for generalists, however, was not specifically driven by the recruitment of either rare or abundant members, suggesting that taxon's initial abundance is minor relevant to the growth of generalists. Patterns in phylogenetic relatedness indicated that environmental filtering was the most influential assembly mechanism for specialists, whereas competitive interaction was more important for the assembly of generalists. Altogether, this study shows that large salinity changes promote the establishment of habitat specialists and that deterministic processes vary during community assembly for ecologically dissimilar taxa. We, therefore, propose that distinguishing assembly mechanisms of different community members helps understand and predict community dynamics in response to environmental change.     

Species pool structure determines the level of generalism of island parasitoid faunas

Aim To examine whether island parasitoid faunas are biased towards generalists when compared with the mainland and their species pool, and to evaluate the effects of climate, island characteristics and regional factors on the relative proportions of idiobionts (i.e. generalists) and koinobionts (i.e. specialists) of two parasitic wasp families, Braconidae and Ichneumonidae. Location Seventy‐three archipelagos distributed world‐wide. Methods We used data on the distribution and biology obtained from a digital catalogue and several literature sources. We related level of generalism, measured as the ratio between the number of idiobiont and koinobiont species, to climatic, physiographic and regional factors using generalized linear models. We compared models by means of Akaike weighting, and evaluated the spatial structure of their residuals. We used partial regressions to determine whether the final models account for all latitudinal structure in the level of generalism. Results Islands host comparatively more idiobionts than continental areas. Although there is a latitudinal gradient in the level of generalism of island faunas correlating with both environmental factors and island characteristics, the most important determinant of island community structure is their source pool. This effect is stronger for ichneumonids, where generalism is higher in the Indomalayan region, arguably due to the higher diversity of endophytic hosts in its large rain forests. Main conclusions The level of generalism of island parasitoid faunas is largely constrained by regional factors, namely by the structure of the species pool, which emphasizes the importance of including regional processes in our understanding of the functioning of ecological communities. The fact that generalist species are more predominant in islands with a large cover of rain forests pinpoints the importance of the indirect effects of ecological requirements on community structure, highlighting the complex nature of geographical gradients of diversity.     

Eco-evolutionary drivers of avian migratory connectivity

Migratory connectivity, reflecting the extent by which migrants tend to maintain their reciprocal positions in seasonal ranges, can assist in the conservation and management of mobile species, yet relevant drivers remain unclear. Taking advantage of an exceptionally large (~150,000 individuals, 83 species) and more-than-a-century-long dataset of bird ringing encounters, we investigated eco-evolutionary drivers of migratory connectivity in both short- and long-distance Afro-Palearctic migratory birds. Connectivity was strongly associated with geographical proxies of migration costs and was weakly influenced by biological traits and phylogeny, suggesting the evolutionary lability of migratory behaviour. The large intraspecific variability in avian migration strategies, through which most species geographically split into distinct migratory populations, explained why most of them were significantly connected. By unravelling key determinants of migratory connectivity, our study improves knowledge about the resilience of avian migrants to ecological perturbations, providing a critical tool to inform transboundary conservation and management strategies at the population level.     

Biogeographic responses and niche occupancy of microbial communities following long-term land-use change

Understanding the effects of forest-to-agriculture conversion on microbial diversity has been a major goal in soil ecological studies. However, linking community assembly to the ruling ecological processes at local and regional scales remains challenging. Here, we evaluated bacterial community assembly patterns and the ecological processes governing niche specialization in a gradient of geography, seasonality, and land-use change, totaling 324 soil samples, 43 habitat characteristics (abiotic factors), and 16 metabolic and co-occurrence patterns (biotic factors), in the Brazilian Atlantic Rainforest, a subtropical biome recognized as one the world’s largest and most threatened hotspots of biodiversity. Pairwise beta diversities were lower in pastures than in forest and no-till soils. Pasture communities showed a predominantly neutral model, regarding stochastic processes, with moderate dispersion, leading to biotic homogenization. Most no-till and forest microbial communities followed a niche-based model, with low rates of dispersal and weak homogenizing selection, indicating niche specialization or variable selection. Historical and evolutionary contingencies, as represented by soil type, season, and dispersal limitation were the main drivers of microbial assembly and processes at the local scale, markedly correlated with the occurrence of endemic microbes. Our results indicate that the patterns of assembly and their governing processes are dependent on the niche occupancy of the taxa evaluated (generalists or specialists). They are also more correlated with historical and evolutionary contingencies and the interactions among taxa (i.e., co-occurrence patterns) than the land-use change itself.

     

Elevational differentiation accelerates trait evolution but not speciation rates in Amazonian birds

The importance of ecologically mediated divergent selection in accelerating trait evolution has been poorly studied in the most species‐rich biome of the planet, the continental Neotropics. We performed macroevolutionary analyses of trait divergence and diversification rates across closely related pairs of Andean and Amazonian passerine birds, to assess whether the difference in elevational range separating species pairs – a proxy for the degree of ecological divergence – influences the speed of trait evolution and diversification rates. We found that elevational differentiation is associated with faster divergence of song frequency, a trait important for pre‐mating isolation, and several morphological traits, which may contribute to extrinsic post‐mating isolation. However, elevational differentiation did not increase recent speciation rates, possibly due to early bursts of diversification during the uplift of the eastern Andes followed by a slow‐down in speciation rate. Our results suggest that ecological differentiation may speed up trait evolution, but not diversification of Neotropical birds.     

The Flight Apparatus of Migratory and Sedentary Individuals of a Partially Migratory Songbird Species

Variations in the geometry of the external flight apparatus of birds are beneficial for different behaviors. Long-distance flight is less costly with more pointed wings and shorter tails; however these traits decrease maneuverability at low speeds. Selection has led to interspecific differences in these and other flight apparatuses in relation to migration distance. If these principles are general, how are the external flight apparatus within a partially migratory bird species shaped in which individuals either migrate or stay at their breeding grounds? We resolved this question by comparing the wing pointedness and tail length (relative to wing length) of migrant and resident European blackbirds (Turdus merula) breeding in the same population. We predicted that migrant blackbirds would have more pointed wings and shorter tails than residents. Contrary to our predictions, there were no differences between migrants and residents in either measure. Our results indicate that morphological differences between migrants and residents in this partially migratory population may be constrained.