Metapopulation Dynamics Research Articles

Reactivity, Attenuation, and Transients in Metapopulations

Transient dynamics often differ drastically from the asymptotic dynamics of systems. In this paper we analyze transient dynamics in birth-jump metapopulations where dispersal occurs immediately after birth (e.g., via larval dispersal). We address the choice of appropriate norms as well as the effect of stage structure on transient dynamics. We advocate the use of the $\ell_1$ norm, because of its biological interpretation, and extend the transient metrics of reactivity and attenuation to birth-jump metapopulations in this norm. By way of examples we compare this norm to the more commonly used $\ell_2$ norm. Our focus is the case where transient dynamics are very different than asymptotic dynamics. We provide simple examples of metapopulations where this is the case and also show how increasing the number of habitat patches can increase this difference. We then connect the reactivity and attenuation of metapopulations to the source-sink classification of habitat patches and demonstrate how to meaningfully measure reactivity when metapopulations are stage-structured, with a focus on marine metapopulations. Our paper makes three primary contributions. First, it provides guidance to readers as to the appropriate norm and scalings for studying transients in birth-jump metapopulations. Second, it provides three examples of transient behavior in metapopulations involving slow-fast systems, crawl-bys, and high dimensionality. Third, it connects the concepts of reactivity and attenuation to the source-sink classification of habitat patches more commonly found in marine metapopulations.

Predicting harvest impact and establishment success when translocating highly mobile and endangered species

Abstract Harvesting individuals for translocations can negatively impact source populations, a critical challenge for species reduced to small populations. Consequently, translocation cohorts often remain small, reducing the establishment probability at the destination. Balancing the potential benefits and risks of such translocations is further complicated by philopatry and natural metapopulation dynamics if the target species is highly mobile. These challenges highlight the importance of translocation feasibility assessments, but such assessments often remain qualitative to date. The critically endangered Kuaka (Whenua Hou Diving Petrel; Pelecanoides whenuahouensis) is a philopatric, highly mobile seabird that could benefit from conservation translocations, but only one small population remains. Through expert elicitations with a user‐friendly Shiny app, we developed a novel metapopulation extension to an integrated population model fitted to long‐term data, allowing us to simultaneously project harvest impact on the source and establishment of destination populations under alternative translocation scenarios, while accounting for philopatry and metapopulation dynamics. Establishment of a destination population without excessive impact on the source was possible, but subject to uncertainty about philopatry and metapopulation dynamics. Accounting for juveniles returning to the source post‐translocations reduced impact on the source, but also decreased establishment at the destination. Natural movements of adults and juveniles between source and destination populations were predicted to modulate effects of different harvest intensities. Synthesis and application. Using state‐of‐the art integrated population models and expert elicitations, we illustrate how translocation feasibility can be evaluated transparently and quantitatively, even when targeting endangered, philopatric and highly mobile species. Our approach is a considerable improvement on current qualitative feasibility assessments. However, we also illustrate that, ultimately, the favoured translocation strategy depends on balancing biological and other fundamental objectives inherent to translocations. Therefore, the ideal strategy cannot be determined solely mathematically, and feasibility assessments should incorporate explicit value statements. Our methodology is applicable to any future translocation scenario.

Asynchrony, density dependence, and persistence in an amphibian.

Understanding drivers of metapopulation dynamics remains a critical challenge for ecology and conservation. In particular, the degree of synchrony in metapopulation dynamics determines how resilient a metapopulation is to a widespread disturbance. In this study, we used 21 years of egg mass count data across 64 nonpermanent freshwater ponds in Connecticut, USA to evaluate patterns of abundance and growth and to assess regional as well as local factors in shaping the population dynamics of wood frogs (Rana sylvatica=Lithobates sylvaticus). In particular, we asked whether a species known to undergo metapopulation dynamics exhibited spatial synchrony in abundances. With the exception of a single year when breeding took place during severe drought conditions, our analyses revealed no evidence of synchrony despite close proximity (mean minimum distance < 300 m) of breeding ponds across the 3213-ha study area. Instead, local, pond-scale conditions best predicted patterns of abundance and population growth rate. We found negative density dependence on population growth rate within ponds as well as evidence that larger neighboring pond populations had a negative effect on focal ponds. Beyond density, pond depth was a critical predictor; deeper ponds supported larger populations. Drought conditions and warm winters negatively affected populations. Overall, breeding ponds vary in critical ways that either support larger, more persistent populations or smaller populations that are not represented by breeding pairs in some years. The infrequency of spatial synchrony in this system is surprising and suggests greater resilience to stressors than would have been expected if dynamics were strongly synchronized. More generally, understanding the characteristics of systems that determine synchronous population dynamics will be critical to predicting which species are more or less resilient to widespread disturbances like land conversion or climate change.

Adjacent crop type impacts potential pollinator communities and their pollination services in remnants of natural vegetation

AbstractAimPollination plays a crucial role in the conservation of many plant species persisting in fragmented, human‐dominated landscapes. Pollinators are known to be instrumental in maintaining genetic diversity and metapopulation dynamics for many plant species and are important for providing ecological services that are essential in agricultural landscapes where populations of native plants are highly isolated. Numerous studies have explored the value of remnant native vegetation for supporting pollination services to crop species, yet the effect of mass‐flowering crops on the pollinator communities and the pollination services they provide to native plant communities persisting in fragmented landscapes are less well understood. Here, we assess the influence of the presence and phenology of a mass‐flowering crop to pollinator community structure, abundance, and pollen load composition in remnant vegetation in complex agricultural landscapes.LocationSouth‐west Western Australia, Australia.MethodsWe recorded the composition and abundance of insect flower visitors and their pollen loads in isolated remnants of York Gum‐Jam woodlands adjacent to canola (insect‐attracting) or wheat (non‐insect‐attracting) fields over two years.ResultsAll bees were much more sensitive to adjacent crop type (neighbouring canola or wheat) than non‐bee pollinators. Honeybees were the most abundant pollinators in canola fields during peak flowering. Honeybee abundance increased in canola‐adjacent reserves post canola bloom, potentially indicating a movement into reserves as crop flowering waned. Native bees were the most diverse in remnant vegetation. Pollen loads of native bees were more mixed (increased pollen richness and evenness) when sampled next to canola fields compared to wheat fields.Main conclusionThe availability of potential insect pollinators to remnant wildflower communities in agricultural landscapes is context dependent. Whether sampled communities were adjacent to wheat or canola in a landscape significantly impacted the abundance of potential pollinators in certain landscape elements, but not others, and the composition of pollen loads carried by these insects. Results offer novel insights about the influence of landscape context on pollinator communities and the potential pollination services available for the conservation of native plant species in highly fragmented agricultural landscapes.

Comparative exploratory movements of two terrestrial isopods (suborder: Oniscidea), in response to humidity and availability of food

Abstract Unfavourable conditions within familiar environments may prompt organisms to make forays into other habitats, at least temporarily. This behaviour is in turn linked to key demographic processes such as immigration, emigration, and eventually, metapopulation dynamics. How such movements are triggered by environmental conditions (much less their interaction effects) has rarely been experimentally tested. To address this, we examined how environmental conditions (3 levels of food and 3 levels of humidity) within a microcosm affect the movements of two species of isopods (Armadillidium vulgare and Porcellio scaber) out of their familiar habitat. We used web-camera checkpoints to record the movements of individually marked animals as they conducted forays along corridors that lead to new, unused habitats. Thirty-six trials were run in total for each species, with each trial involving 16 animals (8 ♂♂, 8 ♀♀). Relatively unfavourable conditions of low humidity, low food levels, and their interaction prompted changes to all the foray metrics we measured. However, different levels of mobility and tolerance to desiccation between the two species also appeared linked to the degree of responses, e.g., Porcellio demonstrated a greater tendency to depart from familiar habitat under low humidity, possibly due to their superior mobility and greater susceptibility to desiccation. This study improves our understanding of how different environmental conditions act in concert to affect the exploratory movements away from familiar habitat, and how these responses differ even for closely-related species.

“Engaging the Enemy”: Orangutan (Pongo pygmaeus morio) Conservation in Human Modified Environments in the Kinabatangan floodplain of Sabah, Malaysian Borneo

Throughout the equatorial tropics, forest conversion to agriculture often fragments crucial primate habitat. In 30 years, 80% of the alluvial lowland forests along the Kinabatangan River in Sabah, Malaysian Borneo, have been supplanted by oil palm (Elaeis guineensis) plantations. Today, only about 20% of the former orangutan (Pongo pygmaeus morio) population remains in the region. Because most of the land is now under the tenure of agribusiness companies, we used a pragmatic approach of mixed biosocial methods and citizen science engagement of oil palm growers (N = 6) as active conservation partners to study orangutan use of the privately administered landscape between protected forest fragments. We found that 22 of 25 remanent forest patches (0.5 to 242 hectares) surveyed within plantations contained food or shelter resources useful for orangutans. Of these, 20 are in regular transitory use by wider-ranging adult male orangutans, and in 9 patches, females are resident and raising offspring isolated within oil palm plantations. These findings indicate that orangutans retain a measure of normal metapopulation dynamics necessary for viability at the landscape level despite drastic habitat modification. We found that barriers to in situ conservation in these agroforest matrices were due to the following misconceptions across sectors: 1) Good farming practices require exclusion of wildlife; 2) Orangutans seen in plantations must be “rescued” by people; and 3) Translocation is an appropriate conservation strategy, and nondetrimental to orangutans. Our exploratory study exemplifies the value of biosocial methods and collaboration with industrial-scale farmers to support primate resilience in forests fragmented by agriculture.

Metapopulation dynamics of multiple species in a heterogeneous landscape

AbstractCharacterizing the diversity of demographic strategies among species can inform research in topics such as trait syndromes, community stability, coexistence, and ecological succession. However, this diversity can depend on the spatial scale considered: at the landscape scale, species often form metapopulations, that is sets of local, sometimes short‐lived, populations, inhabiting discrete habitat patches. Metapopulation dynamics are most frequently analyzed in individual species or pairs of interacting species because of the large amount of data required for multiple species, and because species vary in their perceptions of what constitutes a favorable or unfavorable habitat. Here we evaluate, using a case study, whether a metapopulation model can be used to generate accurate estimates of demographic parameters and to describe the diversity of dynamics, responses to environment, and prospects of long‐term persistence in a guild of species inhabiting a common fragmented landscape. We applied this approach to a guild of 22 mollusk species that inhabit freshwater habitats on two islands of Guadeloupe, to compare metapopulation dynamics among species. We analyzed a 15‐year time series of occupancy records for 278 sites using a multistate occupancy model that estimated colonization and extinction rates as a function of site‐specific and year‐specific environmental covariates, then used model results to simulate future island metapopulation dynamics. Despite the diverse array of metapopulation trajectories—a mix of species with either stable, increasing, declining, or fluctuating metapopulations—and the inherent challenges associated with such data (e.g., imperfect detection, spatial and temporal heterogeneity), our model accurately captured among‐patch variation in suitability for many mollusk taxa. The dynamics of rare species or species with habitat preferences not fully captured by the retained set of covariates were less well described. For several species, we detected a negative correlation between extinction and colonization. This variation in habitat suitability created species‐specific extinction‐resistant pockets in the landscape. Our comparative analysis also revealed that species had distinct strategies for metapopulation dynamics, such as “fast‐turnover” species with both a high proportion of occupied sites and a high rate of site extinction in the landscape.

A river-based approach in reconstructing connectivity among protected areas: Insights and challenges from the Balkan region

Global efforts to halt biodiversity loss mandate the establishment of protected areas. In the face of habitat loss and climate uncertainty, large-scale networks of protected areas connected by corridors are needed to increase the dispersal and persistence potential of biota. For example, the recent European Biodiversity Strategy for 2030 defines clear targets for identifying, establishing and integrating ecological corridors, as part of a Trans-European Nature Network. Here, we examined whether rivers could serve as such corridors, facilitating landscape connectivity (i.e. extent to which landscape facilitates or impedes species movement, exchange of genes, natal dispersal and metapopulation dynamics) among protected areas hosted within different countries in the Balkan Peninsula, southeastern Europe. To quantitatively address this question, we calculated the proportion of the river network enclosed within a protected area per country to detect patterns of protection coverage and explored the degree to which spatial connections between 1878 protected areas are supported by the river network. Acknowledging that dams hinder instream continuity, we further quantified potential loss of connections between protected areas caused by the existence of already implemented or planned dam projects upon critical river habitats of endangered fish species. Our results highlight that Balkan rivers have great potential in providing the spatial connections needed to establish landscape connectivity between most of protected areas in the region. Still, heedless hydropower growth and dissimilarities in river protection between neighboring countries remain key challenges for the evolution of a relative framework. Transnational cooperation and systematic planning of infrastructure development could be the only efficient steps towards supporting the establishment of a river-based network to reconstruct connectivity between protected areas and meet biodiversity goals.

Project ButterBike, or Migrating with Monarchs

Dykman, Sara. 2021. Bicycling with Butterflies: My 10,201-Mile Journey Following the Monarch Migration. Timber Press, Portland, Oregon, USA. The Eastern North American monarch migration, spanning multiple countries and thousands of miles, has long fascinated ecologists, evolutionary biologists, and people of all backgrounds and ages alike. In Bicycling with Butterflies: My 10,201-mile Journey Following the Monarch Migration, Sara Dykman chronicles her expedition across Mexico, the United States, and Canada, cycling along monarch migration routes for nine months. Dykman is a gifted science communicator; she expertly walks readers through phenomena ranging from monarch physiology to coevolution to metapopulation dynamics, using language that is accessible to the general public but still informative to scientists. In this way, it is reminiscent of texts like Anurag Agrawal’s Monarchs and Milkweed (2017) and Sharman Apt Russell’s An Obsession with Butterflies (2004), but it stands out in that each phenomenon is vividly illustrated with Dykman’s personal anecdotes against the backdrop of her epic trip. The book is also an encyclopedia of the people who work with and advocate for monarch butterflies. Dykman details her interactions with guides to the sanctuaries in Mexico, Monarch Watch conservation specialists, “monarch celebrities,” and scientists alike, embodying them with glimpses into their conservation-focused backyards and homes that serve as waypoints throughout her journey. The practical details of her trip are also interesting. The themes of living on the road and cobbling together equipment may seem familiar to field biologists, and the logistics of undertaking such a long bicycle tour alone are fascinating. It is also where a missed opportunity for photographs stands out; as she describes biking along the Mississippi River, the Trans-Canada Highway, and the many other locales, some pictures would have been helpful, especially alongside her vivid descriptions of the ecological and cultural communities associated with each place. The map at the beginning of the book anchors each point of her route to the timing of each chapter effectively, but detailed pictures embedded in the chapters would have added extra clarity. Dykman’s perspective is an interesting one, as a person so captivated by monarch butterflies that she was motivated to bike the entirety of their migration route. In every chapter, her concern for the monarchs and wildlife in general is palpable as she stops to talk to passers-by about the environmental crisis and teach them when best to mow lawns to avoid killing insects, or to pick butterflies and turtles off the road. The gravity with which Dykman approaches these sections can seem a little heavy-handed in the bleakness of her outlook; although she is clearly earnest in trying to communicate the urgency of the situation to her readers, I imagine that most of her audience will already share her sentiments. In places, she also personifies the monarchs, which sometimes seems out of place besides the factually oriented sections on biology. In general, Bicycling with Butterflies is a worthwhile read, with pertinent pieces of information for everyone including cyclists, travelers, and people interested in ecology or the natural world. It serves both as an intriguing ecologist’s travel journal and as a thoughtfully presented compendium of monarch-related information.

Fine Scale Microevolutionary and Demographic Processes Shaping a Wild Metapopulation Dynamics of the South American Fruit Fly Anastrepha fraterculus.

Anastrepha fraterculus (Wiedmann)is an important American pest species. Knowledge of its population dynamics is of particular interest for ecology, evolutionary biology, and management programs. In the present study, phenotypic, genotypic, and spatial data were combined, within the frame of landscape genetics, to uncover the spatial population genetic structure (SGS) and demographic processes of an Argentinian local population from the Yungas ecoregion. Eight simple sequence repeats (SSR) loci and six morphometric traits were analysed considering the hierarchical levels: tree/fruit/individual. Genetic variability estimates were high (HE = 0.72, RA = 4.39). Multivariate analyses of phenotypic data showed that in average 52.81% of variance is explained by the tree level, followed by between individuals 28.37%. Spatial analysis of morphological traits revealed a negative autocorrelation in all cases. SGS analysis and isolation by distance based on SSR showed no significant autocorrelation for molecular coancestry. The comparison between phenotypic (PST) and molecular (FST) differentiation identified positive selection in different fruits for all traits. Bayesian analysis revealed a cryptic structure within the population, with three clusters spatially separated. The results of this study showed a metapopulation dynamics. The genetic background of the components of this metapopulation is expected to change through time due to seasonality, repopulation activities, and high gene flow, with an estimated dispersal ability of at least 10km. Effective population size (Ne) of the metapopulation was estimated in around 800 flies, and within subpopulations (clusters) Ne was associated with the levels of genetic drift experienced by the founding lineages.

Cumulative stressors impact macrofauna differentially according to sandy beach type: A meta-analysis

Many studies have demonstrated human impacts on sandy beach macroinvertebrates. However, little is known about causative drivers among multiple co-occurring stressors and how these interact with natural habitat conditions to yield specific faunal responses. We performed a global meta-analysis to shed light on how interactions between human disturbances and beach morphodynamics shape macroinvertebrate populations. We found that supralittoral forms (Talitridae and Ocypodidae) responded more negatively to the Human Modification Metric (a proxy for urbanization) on dissipative beaches, whereas intertidal organisms (Hippidae and Cirolanidae) showed more negative responses on non-dissipative beaches. Based on these findings we propose the Cumulative Harshness Hypothesis (CHH), which predicts higher sensitivity of beach macroinvertebrates to human disturbances when inhabiting a harsher physical environment according to their life histories. Secondly, we compared the response of macroinvertebrates to urbanization levels from local to larger scales (from 500 to 50000 m). Supralittoral families responded more negatively to local urbanization, which leads to habitat loss due to removal or reduction of upper beach zones. Conversely, intertidal organisms with planktonic larval stages were more affected by urbanization at the largest spatial scales, which we hypothesize disrupts metapopulation dynamics by impacting the supply of larvae that could colonize human-disturbed beaches. The differential effects of human disturbances on macroinvertebrates according to beach morphodynamics suggest that the efficiency of these ecological indicators for beach monitoring is context-dependent. Focusing on multiple stressors rather than on a single one is also critical to mitigate human impacts on these threatened ecosystems.

Fragmentation of lateral connectivity and fish population dynamics in large rivers

AbstractLateral Hydrological Connectivity (LHC) has been extensively fragmented in river–floodplain ecosystems of the world. Uncertainties about how LHC affects fishes are great, impeding the design of effective rehabilitation strategies. Existing conceptual frameworks do not provide sufficient mechanistic detail to support the novel decision problems river managers face. We offer a framework of how LHC affects fishes in river–floodplain ecosystems that is, process‐based, integrates all life‐stages and is spatial; these features, we argue, are required to assess risks and opportunities associated with different LHC rehabilitation strategies. Within river–floodplain segments, LHC affects population processes through five ‘effect‐classes’: effects of floodplain habitat (1) and channel habitat (2); effects of material subsidies from the floodplain to the channel (3) andvice versa(4); and effects of connectivity on lateral dispersal (5). The relative influence of these effect‐classes on processes varies among species and life‐stages. At the scale of the drainage basin, inter‐segment variation in geomorphology generates a longitudinal source‐sink structure to habitat quality and quantity, pointing to a need to better understand fish metapopulation dynamics in river–floodplain ecosystems. Given the significant investment in trying to restore river–floodplain ecosystems, we highlight potentially costly and ineffective LHC management decisions. These include certain heavily engineered LHC rehabilitation strategies that do not promote critical population processes at a local scale, and at basin scales implementing strategies that do not facilitate the metapopulation processes that promote species’ persistence.

The relationship between pathogen life-history traits and metapopulation dynamics.

Summary Plant pathogen traits, such as transmission mode and overwintering strategy, may have important effects on dispersal and persistence, and drive disease dynamics. Still, we lack insights into how life‐history traits influence spatiotemporal disease dynamics.We adopted a multifaceted approach, combining experimental assays, theory and field surveys, to investigate whether information about two pathogen life‐history traits – infectivity and overwintering strategy – can predict pathogen metapopulation dynamics in natural systems. For this, we focused on four fungal pathogens (two rust fungi, one chytrid fungus and one smut fungus) on the forest herb Anemone nemorosa.Pathogens infecting new plants mostly via spores (the chytrid and smut fungi) had higher patch occupancies and colonization rates than pathogens causing mainly systemic infections and overwintering in the rhizomes (the two rust fungi). Although the rust fungi more often occupied well‐connected plant patches, the chytrid and smut fungi were equally or more common in isolated patches. Host patch size was positively related to patch occupancy and colonization rates for all pathogens.Predicting disease dynamics is crucial for understanding the ecological and evolutionary dynamics of host–pathogen interactions, and to prevent disease outbreaks. Our study shows that combining experiments, theory and field observations is a useful way to predict disease dynamics.

The role of wind in controlling the connectivity of blue mussels (Mytilus edulis L.) populations

BackgroundLarval connectivity between distinct benthic populations is essential for their persistence. Although connectivity is difficult to measure in situ, it can be predicted via models that simulate biophysical interactions between larval behaviour and ocean currents. The blue mussel (Mytilus Edulis L.) is widespread throughout the northern hemisphere and extensively commercialised worldwide. In the Irish Sea, this industry represents ~ 50% of Welsh shellfisheries, where cultivation is mainly based on wild spat. However, the main sources and amount of spat varied interannually (1100 tonnes harvest in 2014 against zero in 2018). The aim of this study is to characterise the structure and dynamics of the blue mussel metapopulation within the northern part of the Irish Sea.MethodsWe develop a Lagrangian particle tracking model, driven by a high-resolution (from 30 to 5000 m) validated unstructured coastal hydrodynamic model of the Irish Sea, to simulate spatial and temporal variability of larval dispersal and connectivity between distinct mussel populations and potential settlement areas.ResultsOur results showed that: (1) larvae positioned near the surface were strongly influenced by wind-driven currents suggesting that connectivity networks had the potential to span hundreds of kilometres; (2) in contrast, larvae positioned deeper in the water column were driven by tidal currents, producing intricate spatial patterns of connectivity between mussel beds over tens of kilometres that were consistent over time.ConclusionsDispersal of mussel larvae in the tidally energetic Irish Sea during the April–May spawning season is potentially driven by wind-driven surface currents, as confirmed by fisherman observations of inter-annual variability in wild spat collection. These results have important implications for metapopulation dynamics within the context of climate change and sustainable shellfisheries management (i.e. gain and loss of populations and harvest areas according to wind conditions).

Strong spatial population structure shapes the temporal coevolutionary dynamics of costly female preference and male display

Female mating preferences for exaggerated male display traits are commonplace. Yet, comprehensive understanding of the evolution and persistence of costly female preference through indirect (Fisherian) selection in finite populations requires some explanation for the persistence of additive genetic variance (V a) underlying sexual traits, given that directional preference is expected to deplete V a in display and hence halt preference evolution. However, the degree to which V a, and hence preference‐display coevolution, may be prolonged by spatially variable sexual selection arising solely from limited gene flow and genetic drift within spatially structured populations has not been examined. Our genetically and spatially explicit model shows that spatial population structure arising in an ecologically homogeneous environment can facilitate evolution and long‐term persistence of costly preference given small subpopulations and low dispersal probabilities. Here, genetic drift initially creates spatial variation in female preference, leading to persistence of V a in display through “migration‐bias” of genotypes maladapted to emerging local sexual selection, thus fueling coevolution of costly preference and display. However, costs of sexual selection increased the probability of subpopulation extinction, limiting persistence of high preference‐display genotypes. Understanding long‐term dynamics of sexual selection systems therefore requires joint consideration of coevolution of sexual traits and metapopulation dynamics.

Improved chromosome-level genome assembly of the Glanville fritillary butterfly (Melitaea cinxia) integrating Pacific Biosciences long reads and a high-density linkage map.

BackgroundThe Glanville fritillary (Melitaea cinxia) butterfly is a model system for metapopulation dynamics research in fragmented landscapes. Here, we provide a chromosome-level assembly of the butterfly's genome produced from Pacific Biosciences sequencing of a pool of males, combined with a linkage map from population crosses.ResultsThe final assembly size of 484 Mb is an increase of 94 Mb on the previously published genome. Estimation of the completeness of the genome with BUSCO indicates that the genome contains 92–94% of the BUSCO genes in complete and single copies. We predicted 14,810 genes using the MAKER pipeline and manually curated 1,232 of these gene models.ConclusionsThe genome and its annotated gene models are a valuable resource for future comparative genomics, molecular biology, transcriptome, and genetics studies on this species.

A unique diploid – triploid contact zone provides insights into the evolutionary mechanisms of cytotype coexistence in flowering rush (Butomus umbellatus)

Polyploidisation is an important evolutionary force in land plants. Due to its recurrent incidence, many plant species retain individuals of two or more different ploidy levels. However, particular ecological and evolutionary mechanisms facilitating intraspecific cytotype coexistence have been identified for just a handful of species and cannot yet be generalised. Our pilot data have revealed a unique complex of mixed diploid-triploid populations of the marshland perennial Butomus umbellatus in the Eastern Slovak Lowland (eastern Central Europe). Intensive flow-cytometric ploidy screening of 1,230 individuals sampled from 72 populations was conducted at both regional and local (within-population) scales to assess cytotype distribution patterns. Vegetation assessments along with phenotypic comparisons of cytotypes directly in the field and later under common garden cultivation served to provide insight into mechanisms of cytotype coexistence. Altogether 42 % of the sampled populations were mixed-ploidy, pointing to unexpectedly high rates of diploid-triploid coexistence. While the cytotype distribution was random at the regional scale, significant spatial clustering occurred at the local scale. No ecological niche differences between the cytotypes were detected. Triploids attained greater values of several morphological characters both in the field and under cultivation, differences in the shape of inner tepals even show potential for cytotype discrimination. Both cytotypes exhibited high and comparable investments into clonal traits, reproductive assurance provided by asexual reproduction likely plays a key role in cytotype coexistence and triploid predominance. The common cytotype coexistence in this region seems to be also facilitated by periodical seasonal floods promoting transport of vegetative propagules among populations (i.e. metapopulation dynamics) and providing long-term continuity of favourable sites by recurrent disturbances.

Editorial 2022

Editorial 2022

Network topology and patch connectivity affect dynamics in experimental and model metapopulations.

Biological populations are rarely isolated in space and instead interact with others via dispersal in metapopulations. Theory predicts that network connectivity patterns can have critical effects on network robustness, as certain topologies, such as scale-free networks, are more tolerant to disturbances than other patterns. However, at present, experimental evidence of how these topologies affect population dynamics in a metapopulation framework is lacking. We used experimental metapopulations of the aquatic protist Paramecium tetraurelia to determine how network topology influences occupation patterns. We created metapopulations engineered to be comparable in linkage density, but differing in their degree distribution. We compared random networks to scale-free networks by evaluating local population occupancy and abundance throughout 18-30 protist generations. In parallel, we used simulations to explore differences in patch occupation patterns among topologies. Our experimental results highlighted the importance of the balance between dispersal and extinction in the interaction with spatial network topology. Under low dispersal conditions, random metapopulations of P. tetraurelia reached higher abundance and higher occupancy (proportion of occupied patches) compared to scale-free systems in both experimental and simulated systems. Under high dispersal conditions, we did not detect differences between types of metapopulations. Increasing patch degree (i.e. number of connections per patch) reduced the probability of extinction of local populations in both types of networks. We suggest the interaction between colonization/extinction rates and network topology alters the likelihood of rescue effects which results in differential patterns of occupancy and abundance in metapopulations.

Dispersal of aquatic invertebrates by lesser black-backed gulls and white storks within and between inland habitats

Waterbirds can transport aquatic invertebrates internally, contributing to metapopulation dynamics between aquatic habitats in a terrestrial matrix. However, research into this dispersal process to date has focused on individual field sites or laboratory studies. We investigated the invertebrates dispersed by endozoochory by the lesser black-backed gull Larus fuscus wintering in Andalusia, south-west Spain in 2016–2017, comparing seven sites interconnected by their movements, with different degrees of anthropogenization [three landfills, two saltpan complexes, a natural lake, and a large (370 km2) ricefield area]. In the ricefields, we also compared invertebrates dispersed by gulls with those dispersed by the larger white stork Ciconia ciconia. A total of 642 intact invertebrates and their propagules (mainly plumatellid bryozoans, cladocerans, and other branchiopods) were recorded in excreta (faeces and pellets) from gulls and storks. A greater diversity and abundance of invertebrates were recorded in ricefields, notably 43 individuals of the alien snail Physella acuta. One snail was still alive in a gull pellet 3 weeks after being stored in a fridge. This represents the first record of snail dispersal within waterbird pellets. Viability was also confirmed for the cladoceran Macrothrix rosea recorded in ricefields, and the alien brine shrimp Artemia franciscana recorded mainly in saltpans. In ricefields, gulls and pellets had significantly fewer propagules and fewer taxa per gram of excreta than storks and faeces, respectively. Through their high mobility, gulls and storks can disperse invertebrates between different natural and artificial habitats, and even to landfills. They can promote metapopulation dynamics for native bryozoans and branchiopods, but also the spread of invasive snails and brine shrimp.