Long-distance Dispersal Research Articles

New finding on a migratory bird, the fowl tick Argas (Persicargas) persicus (Oken, 1818), in Italy

Migratory birds reach Europe from sub-Saharan Africa, and some avian species may harbor and transport infected ectoparasites, mainly ticks, native to the territories of departure. In 2022, a project focused on identifying the introduction of pathogens in Italy from Africa via migratory birds represented an important opportunity to investigate this particular route of tick dispersal. Among ticks collected from migratory birds on the island of Ventotene, Latium Region, we found one larva of a soft tick on a common whitethroat (Curruca communis) that was morphologically and molecularly identified to the species level as Argas (Persicargas) persicus (Oken 1818). This study reports the fifth detection of this species in Italy; therefore, it is considered very rare. Further monitoring programmes should be implemented to better monitor the spread of this species and possibly update its distribution.

Biome evolution in subfamily Cercidoideae (Leguminosae): a tropical arborescent clade with a relictual depauperate temperate lineage

Some plant lineages remain within the same biome over time (biome conservatism), whereas others seem to adapt more easily to new biomes. The c. 398 species (14 genera) of subfamily Cercidoideae (Leguminosae or Fabaceae) are found in many biomes around the world, particularly in the tropical regions of South America, Asia and Africa, and display a variety of growth forms (small trees, shrubs, lianas and herbaceous perennials). Species distribution maps derived from cleaned occurrence records were compiled and compared with existing biome maps and with the literature to assign species to biomes. Rainforest (144 species), succulent (44 species), savanna (36 species), and temperate (10 species) biomes were found to be important in describing the global distribution of Cercidoideae, with many species occurring in more than one biome. Two phylogenetically isolated species-poor temperate (Cercis) and succulent (Adenolobus) biome lineages are sister to two broadly distributed species-rich tropical clades. Ancestral state reconstructions on a time-calibrated phylogeny suggest biome shifts occurred throughout the evolutionary history of the subfamily, with shifts between the succulent and rainforest biomes, from the rainforest to savanna, from the succulent to savanna biome, and one early occurring shift into (or from) the temperate biome. Of the 26 inferred shifts in biome, three are closely associated with a shift from the ancestral tree/shrub growth form to a liana or herbaceous perennial habit. Only three of the 13 inferred transcontinental dispersal events are associated with biome shifts. Overall, we find that biome shifts tend to occur within the same continent and that dispersals to new continents tend to occur within the same biome, but that nonetheless the biome-conserved and biogeographically structured Cercidoideae have been able to adapt to different environments through time.

Uncharted territory: the arrival of Psychoda albipennis (Zetterstedt, 1850) (Diptera: Psychodidae) in Maritime Antarctica

Despite increasing awareness of the threats they pose, exotic species continue to arrive in Antarctica with anthropogenic assistance, some of which inevitably have the potential to become aggressively invasive. Here, we provide the first report of the globally cosmopolitan species Psychoda albipennis (Diptera, Psychodidae; commonly known as moth flies) in Antarctica during the austral summer of 2021/2022, with the identification confirmed using traditional taxonomic and molecular approaches. The species was present in very large numbers and, although predominantly associated with the drainage and wastewater systems of Antarctic national operator stations in synanthropic situations, it was also present in surrounding natural habitats. While it is unclear if P. albipennis is capable of long-distance dispersal, adult psychodid flies are known to travel more than 90 m from their emergence sites, and up to 1.5 km with wind assistance. Thus, once established in the natural environment of King George Island there appears to be a high risk of the species rapidly becoming invasive. The introduction of non-native species such as P. albipennis can be a significant driver of future biodiversity change and loss, and seriously impact ecosystem health. In vulnerable low diversity ecosystems, such as in the terrestrial environments of Antarctica, non-native species can lead to step changes in ecological functions and interactions, displace native species and, potentially, lead to the extinction of native biota.

Comparative phylogeography of vicariant species of the <i>Daphnia longispina</i> s.lat. complex (Crustacea: Cladocera) in North Eurasia

This study presents new data on population-genetic polymorphism, phylogeny and phylogeography of two vicariant species belonging to the Daphnia longispina s.lat. complex (Crustacea: Cladocera) in northern Eurasia, D. longispina s.str. and D. dentifera. Based on the variability of the fragments of non-coding 12S rRNA and the protein coding ND2 genes of mitochondrial DNA, the demographic processes that took place in populations of this vast region have been reconstructed. The previously suggested hypothesis about the different demographic history of the “Siberian” and “European” D. longispina s.str. clades has not been confirmed, since we first revealed a deep mitochondrial divergence within the “Siberian” clade. Moreover, a new divergent lineage of D. longispina s.str. in Siberia has been identified. Nevertheless, the phylogeographic patterns of D. longispina s.str. and D. dentifera in northern Eurasia confirm the earlier conclusion that repeated, combined effects on their populations of dispersion and vicariate events occurred in different phases of the Pleistocene.

Rowing Against the Tide: The Golden Mussel (Limnoperna fortunei) Leaves DNA Footprints Along Its Invasion Route in South American Rivers

The invasion of the golden mussel has resulted in considerable environmental and socioeconomic alterations, which present a considerable threat to the native biodiversity and sustainability of the region. Understanding the distribution and biological characteristics of this Asian mussel, as well as its interaction with human activities, is of the utmost importance to developing effective strategies for mitigating and preventing its further spread. This study examines the dispersal route and incidence of golden mussels, tracing their movement from initial populations in Argentina to their arrival in the São Francisco River Basin (SFR). The presence of the mussel was confirmed through an integrative assessment that included shell taxonomic analyses and mitochondrial DNA signatures. This assessment identified populations located 7.5 km from the river’s mouth, close to the Atlantic Ocean, in areas such as shrimp farms, artisanal ports, and marinas. The analysis of mitochondrial DNA revealed the presence of South-American-specific and shared ancestral haplotypes in the SFR, Grande River, and Argentina. These findings indicate that intracontinental colonization toward the northeast region of South America originated from Asian populations that entered South America via Argentina. The absence of Asian-specific signatures in the SFR, combined with a geomorphological structure unsuitable for large ports or transoceanic vessels, supports the hypothesis of the intracontinental dispersal of Limnoperna fortunei.

Connectivity of scamp Mycteroperca phenax populations in the United States Gulf of Mexico and Atlantic Ocean

Connectivity among marine fish populations not only arises through the movement of adults but also through larval dispersal facilitated by ocean currents. For species with long pelagic larval duration and high site fidelity as adults, larval dispersal can be the dominant mechanism of connectivity among otherwise spatially distinct populations. Therefore, when assessing the recruitment dynamics or population structure of such species, it is essential to evaluate how larval biology and reproductive ecology interact with oceanographic circulation. To investigate this interaction for scamp Mycteroperca phenax, a grouper found in the Gulf of Mexico and Atlantic Ocean, we simulated the dispersal of millions of virtual larvae throughout the scamp’s range near the southeastern USA. We found a pattern of local retention, with larvae tending to settle close to their spawning location. There was also, however, long-distance dispersal that consistently crossed the boundary between spatial management units. Due to directional patterns in oceanographic transport and spatial differences in abundance, almost one-third of the virtual larvae that settled in the Atlantic came from spawning locations in the Gulf of Mexico, although most of these settled near the boundary between the regions. These patterns were robust to a variety of sensitivity analyses, but the magnitude of connectivity between management units varied. This connectivity has significant implications for stock assessment and fishery management. It may increase the resilience of Atlantic populations, but it also means that the sustainability of Atlantic populations may rely, in part, on the health of spawning populations in the Gulf of Mexico.

Movement Ecology of a Coastal Foundation Seagrass Species: Insights From Genetic Data and Oceanographic Modelling

ABSTRACTAimSeed dispersal plays a key role in shaping the distribution and genetic complexity of seagrass populations and affects their resilience capacity under disturbance. The endemic seagrass Posidonia oceanica is a key component of Mediterranean coastal ecosystems, but knowledge about movement ecology in this species is limited, especially regarding seed movement pathways and dispersal potential.LocationWestern coast of Sicily (central Mediterranean).MethodsBeach‐cast fruits of the Mediterranean seagrass P. oceanica were collected from nine localities along the Western coast of Sicily, along with adult shoots from eight putative donor meadows. We determined pair‐wise genetic differentiation between established meadows and seed cohorts. Genetic assignment tests were used to infer the most likely meadow of origin of individual seeds and were complemented with forward and backward Lagrangian simulations of dispersal.ResultsA significant genetic differentiation was found between seed pools and the most‐likely meadow of origin. The genetic assignment confirmed that seeds from the same cohort originated from multiple meadows and emphasised the presence of long‐distance‐dispersal (LDD) events (up to hundreds of km). Genetic connectivity appeared to be greater than that predicted by oceanographic simulations, which may reflect the longer temporal scales on which gene flow is shaped, in contrast to contemporary dispersal patterns. Lagrangian simulations highlighted that fruits were physically capable of dispersing beyond the study area and that the north Tunisian coast could be a key source of propagules for the populations studied.Main ConclusionsOur study represents a significant step forward in the understanding of P. oceanica movement ecology and could guide meadows' conservation and restoration actions. Our findings are significant in a broader context outside of the research area and could be the basis of similar studies in other regions, especially considering the increasing number of fruiting events recorded across the Mediterranean likely associated with ocean warming.

There and back again: local institutions, an Uruk expansion and the rejection of centralisation in the Sirwan/Upper Diyala region

During the fourth millennium BC, public institutions developed at several large settlements across greater Mesopotamia. These are widely acknowledged as the first cities and states, yet surprisingly little is known about their emergence, functioning and demise. Here, the authors present new evidence of public institutions at the site of Shakhi Kora in the lower Sirwan/upper Diyala river valley of north-east Iraq. A sequence of four Late Chalcolithic institutional households precedes population dispersal and the apparent regional rejection of centralised social forms of organisation that were not then revisited for almost 1500 years.

How fast are viruses spreading in the wild?

Genomic data collected from viral outbreaks can be exploited to reconstruct the dispersal history of viral lineages in a two-dimensional space using continuous phylogeographic inference. These spatially explicit reconstructions can subsequently be used to estimate dispersal metrics that can be informative of the dispersal dynamics and the capacity to spread among hosts. Heterogeneous sampling efforts of genomic sequences can however impact the accuracy of phylogeographic dispersal metrics. While the impact of spatial sampling bias on the outcomes of continuous phylogeographic inference has previously been explored, the impact of sampling intensity (i.e., sampling size) when aiming to characterise dispersal patterns through continuous phylogeographic reconstructions has not yet been thoroughly evaluated. In our study, we use simulations to evaluate the robustness of 3 dispersal metrics - a lineage dispersal velocity, a diffusion coefficient, and an isolation-by-distance (IBD) signal metric - to the sampling intensity. Our results reveal that both the diffusion coefficient and IBD signal metrics appear to be the most robust to the number of samples considered for the phylogeographic reconstruction. We then use these 2 dispersal metrics to compare the dispersal pattern and capacity of various viruses spreading in animal populations. Our comparative analysis reveals a broad range of IBD patterns and diffusion coefficients mostly reflecting the dispersal capacity of the main infected host species but also, in some cases, the likely signature of rapid and/or long-distance dispersal events driven by human-mediated movements through animal trade. Overall, our study provides key recommendations for the use of lineage dispersal metrics to consider in future studies and illustrates their application to compare the spread of viruses in various settings.

Area sharing among tigers in re-introduced population of Sariska tiger reserve demonstrating space crunch in Human dominated landscape

We examined the home range dynamics, dispersal patterns, and space-sharing behaviour of reintroduced tigers and their progenies in different generations in Sariska Tiger Reserve (STR) from 2018 to 2022. During the study period, the tiger population increased from four males and eight females to seven males, 11 females, and three sub-adult females. Mean home ranges were 34 ± 2 km² (SE) for female tigers (n=11) and 95 ± 6 km² for male tigers (n=10), while core activity areas (50% KDE) averaged 6 ± 1 km² for females and 23 ± 3 km² for males. Female home ranges showed a decreasing trend due to natal dispersal by sub-adults, whereas male home ranges expanded due to territorial consolidation. Instances of territorial overlap, including fatal conflicts, highlighted the competitive pressures in this human dominated landscape. To accommodate the growing tiger population and mitigate human-tiger conflicts, we recommend enhanced monitoring, relocation of villages to create inviolate spaces, and strengthening the protection regime.

How Important Is Informed Natal Dispersal for Modelling the Demographic and Genetic Effects of Environmental Variability?

Dispersal is a fundamental ecological process that influences population dynamics and genetic diversity and is therefore an important component of the models used to simulate population responses to environmental change. We considered informed dispersal in relation to settlement location, where individuals could optimise selection of settlement location with regard to per capita resource availability and investigated the importance of this type of informed dispersal for simulated demography and genetic diversity under different biological and environmental scenarios. We used an individual-based simulation model scaled with reference to the ecology of small mammals in fire prone savanna ecosystems. We simulated demographic and genetic processes under informed and uninformed dispersal across several scenarios of life history, environmental heterogeneity (patch size and patch dynamics) and dispersal distance. The effect of the dispersal method on population size far outweighed that of dispersal distance under all combinations of habitat quality, temporal dynamics, patch size and dispersal distance modelled. The effects of habitat patch size and habitat dynamics (representing temporal change in habitat quality such as that potentially generated by disturbance) were low under most of the scenarios modelled. Informed dispersal influenced genetic diversity and differentiation, but the effects were weaker than those of dispersal distance. The genetic effect of informed dispersal occurred through the effect on genetic diversity of the overall metapopulation, while the dispersal distance influenced gene flow and genetic diversity within subpopulations. Informed dispersal was less effective in increasing population size in models of a long-lived species with overlapping generations. This was particularly true when habitat quality was dynamic and natal dispersal choices did not result in lifelong habitat quality outcomes. Our results suggest that including informed decision-making in dispersal in simulation models leads to different projections of demography, genetic diversity and susceptibility to environmental change.

Observation of spatiotemporal dynamics for topological surface states with on-demand dispersion

Dispersion management in guided wave optics is of vital importance for various applications. Topological photonics opens new horizons for manipulating unidirectional guided waves utilizing edge states. However, the experimental observation of spatiotemporal dynamics for guided waves with on-demand dispersion in topological photonic crystal is an important issue awaiting exploitation. Herein, we experimentally investigate the spatiotemporal properties of topological surface states with on-demand dispersion, where they are supported by a truncated valley photonic crystal with surface modulation. We observe the electromagnetic dynamics of surface states with typical dispersions, where dynamical trapping of an electromagnetic pulse mediated by the unidirectional surface state with flat dispersion and backward beam routing using reversed dispersion properties are achieved in photonic crystal slabs. Both numerical and experimental results substantiate the ultimate dispersion management for topological surface states, which could pave new ways for the manipulation of electromagnetic waves on the surface of photonic devices.

The enigmatic Triassic ovulate reproductive structures of Dordrechtites are recurved cupules fundamentally comparable to the cupules of Doylea and similar plants.

Recent paleobotanical discoveries have renewed interest in the distinctively recurved, seed-bearing cupules of Mesozoic plants, which are important for understanding seed plant phylogeny and the origin of the second integument of the angiosperm ovule. Reanalysis of the enigmatic seed-bearing organ Dordrechtites elongatus from the Triassic of South Africa, the type species of the genus, combined with information from similar material from Antarctica, Argentina and Australia, indicates that Dordrechtites is a highly modified lateral branch of a seed cone. Short lateral projections from a primary cone axis each bear several Dordrechtites units. Each unit consists of a long stalk bearing a straight to sometimes recurved cupule with a long distal extension beyond the cupule apex. Each cupule is flattened in a plane perpendicular to the stalk and distal projection and contains up to two seeds. Structural similarities between Dordrechtites and the cupules of Doyleales indicate that they are homologous, providing new evidence for a close relationship. The persistent cupule stalk and apical extension of Dordrechtites, combined with the flattened cupule, suggests modification for wind and water dispersal.

Bluetongue In Brazil: A Spatiotemporal Analysis (2001- 2023)

Background: Bluetongue is a non-contagious viral disease caused by the bluetongue virus (Orbivirus), affecting domestic and wild ruminants, particularly sheep. Transmission occurs primarily through vectors of the genus Culicoides, with distribution influenced by environmental and climatic factors. In Brazil, disease outbreaks are sporadic; however, bluetongue is classified as a notifiable disease due to its economic and epidemiological significance and its potential to be mistaken for foot-and-mouth disease. Materials and Methods: This study analyzed the temporal and spatial distribution of bluetongue outbreaks in Brazil from 2001 to 2023, investigating possible associations with climatic variables such as temperature, precipitation, and wind speed. Data were obtained from the Zoosanitary Information System Panel (MAPA-SIZ) and organized into spreadsheets for statistical analysis. Pearson's correlation test and spatial lag regression were applied using the Jamovi and GeoDa software, respectively. Results: A total of 51 bluetongue virus infection outbreaks were recorded, comprising 482 cases predominantly concentrated in southern Brazil. Sheep were the most affected species (73% of cases), followed by wildlife (20%), goats (6%), and cattle (2%). The analysis revealed a significant inverse correlation between the annual mean temperature and the occurrence of cases and outbreaks (r2=0.306 and r2=0.379 respectively), indicating higher disease prevalence in states with lower temperatures. No statistically significant correlations were observed between disease occurrence and either precipitation or average wind speed. However, international studies suggest that wind can facilitate the long-distance dispersion of Culicoides, while mild temperatures extend vector survival. Conclusion: The results suggest that temperature is a determining factor in the spatial and temporal distribution of bluetongue in Brazil, whereas precipitation and wind speed have limited influence. The sporadic occurrence of the disease underscores the importance of continuous surveillance to prevent outbreaks and improve disease control. Strategies that account for vector population dynamics and climatic conditions could enhance the effectiveness of monitoring and control measures.

Organisms with high dispersal ability as a proxy for biogeographical characterisation of the Mediterranean biome

The Mediterranean biome offers a diverse range of habitats, particularly rocky environments, known for their long-term stability and persistence. Adapted to these rocky surfaces, chasmophytes thrive in this region, benefiting from reduced competition and human interference. The distribution of stress-tolerant cryptogams with generally broad niches represents a significant gap in the biogeography of the region. This study investigates whether complex symbiotic organisms with a potential for long-distance dispersal could serve as biogeographic indicators for delimitation of the Mediterranean biome's boundaries. Through comprehensive chorology data research, saxicolous lichen congeners of the genus Solenopsora were mapped across the Mediterranean Basin as a model area. Environmental predictors (climate and geology) were employed to predict suitable habitats, shedding light on the lichens' ecological niches. Habitat suitability models consistently aligned with the Mediterranean's geographical area, indicating a tight link between lichen distribution and Mediterranean climate classification. While climate change may pose vulnerabilities, no significant range shifts beyond the latitudinal limit of the Mediterranean were predicted. Despite overlapping climatic niches, differences in microhabitat preferences in terms of insolation were observed among studied taxa. Vulnerable regions with potential habitat decreases were identified under future scenarios, emphasizing the importance of environmental heterogeneity in securing local species persistence. This study supports the hypothesis that these lichen symbiotic systems are restricted to the Mediterranean Basin, highlighting their potential to reflect Mediterranean climate, environmental stability, and indicate the boundaries of the Mediterranean biome. Our investigation demonstrates that collection-based research can yield significant contributions to current biogeography.

Engineering Metal-MOF Interfaces for Selective CO2 Hydrogenation to Methanol.

The hydrogenation of CO2 to methanol is a promising pathway toward sustainable fuel production and carbon recycling. A key factor in the efficiency of this process lies in the interaction between the metal catalyst and its support. Metal-Organic Frameworks (MOFs) have emerged as highly effective platforms due to their tunable structures, large surface areas, and ability to form stable interfaces with single-atom metals or metal nanoparticles. These metal-MOF interfaces are crucial for stabilizing active sites, preventing sintering, and enhancing catalytic performance. In this concept paper, we explore the role of these interfaces in promoting CO2 hydrogenation, focusing on Cu-Zn, Cu-Zr, and Zn-Zr interfaces. The formation of strong interactions between metal sites and MOF nodes enables precise control over the dispersion and electronic environment of the active species, significantly improving methanol selectivity and long-term stability. By analyzing recent advancements in MOF-supported catalysts, this work highlights the concept of engineered metal-MOF interfaces to drive the development of next-generation catalysts for efficient methanol synthesis from CO2.

Impact of climate change on the distribution of the invasive water hyacinth in Ethiopia

The introduction of exotic species poses one of the greatest threats to biodiversity globally. Water hyacinth is a dangerous invasive species that has harmed Ethiopia’s wetland ecology and economy. This research aims to evaluate the current distribution of water hyacinth and the impact of environmental variables on its spread, while also mapping future habitat suitability under climate change scenarios and assessing how these changes may influence the species' potential expansion. To estimate the risks of climate change to the species, a predictive model was developed from six modeling methodologies to investigate the climatic suitability of target species for the years 2050 and 2070 under two Representative Concentration Pathway (RCP) scenarios (RCP4.5 and RCP 8.5). Under the current climatic scenario, only 69.78% (789 503.8 km2) and 16.02% (181 262.8 km2) of the country is moderately and highly suitable for species dispersion and invasion respectively. The remaining 14.2% (160 620.9 km2) is unsuitable for the distribution and invasion of the species. In 2050, under the RCP4.5 and RCP 8.5, the ‘highly suitable’ range of water hyacinth is anticipated to expand by 16.35% and 15.39%, whereas the ‘moderately suitable’ area is predicted to increase by 70.81% and 71.52%, respectively. Under the RCP8.5 scenarios, compared to the current climatic conditions, in 2070 the ‘highly suitable’ region for the species is expected to increase by 11.48%. Its continuing growth would exacerbate the issue of ecological and economic crisis, cause significant economic and environmental harm and endanger the community’s way of life. In order to avert or reduce these effects, a thorough examination of water hyacinth along the two RCPs by water resource scientists and mamangers, that takes into account how climate change is affecting water hyacinth growing locations in Ethiopia, and provides a proper solution, is mandatory.

Estimating dispersal rates and locating genetic ancestors with genome-wide genealogies.

Spatial patterns in genetic diversity are shaped by individuals dispersing from their parents and larger-scale population movements. It has long been appreciated that these patterns of movement shape the underlying genealogies along the genome leading to geographic patterns of isolation by distance in contemporary population genetic data. However, extracting the enormous amount of information contained in genealogies along recombining sequences has, until recently, not been computationally feasible. Here we capitalize on important recent advances in genome-wide gene-genealogy reconstruction and develop methods to use thousands of trees to estimate per-generation dispersal rates and to locate the genetic ancestors of a sample back through time. We take a likelihood approach in continuous space using a simple approximate model (branching Brownian motion) as our prior distribution of spatial genealogies. After testing our method with simulations we apply it to Arabidopsis thaliana. We estimate a dispersal rate of roughly 60km2 per generation, slightly higher across latitude than across longitude, potentially reflecting a northward post-glacial expansion. Locating ancestors allows us to visualize major geographic movements, alternative geographic histories, and admixture. Our method highlights the huge amount of information about past dispersal events and population movements contained in genome-wide genealogies.

High Genetic Diversity of Hirudo verbana Carena, 1820 (Annelida: Hirudinea: Hirudinidae) in Romania Confirms That the Balkans Are Refugia Within Refugium

This study presents the first data on the distribution of the Mediterranean medicinal leech Hirudo verbana in Romania, as well as the first molecular characterization of the Romanian populations, using mitochondrial DNA markers. In total, 133 specimens from 19 populations in Romania were surveyed for mitochondrial COI and 12S markers. Available GenBank sequences from other localities throughout Europe were included to place the Romanian populations in a broader phylogeographical context. The Romanian H. verbana samples belong to 23 COI haplotypes, 4 of which are previously known from Serbia and Ukraine, while 19 haplotypes are herein reported for the first time. For 12S, the number of haplotypes identified was 12, from which only 5 are unique to Romania. The Romanian H. verbana cluster within the previously reported eastern phylogroup, known to occur from Serbia to North Caucasus, Turkey, and Uzbekistan. The mismatch distribution analysis and the results of neutrality tests suggest that the Romanian H. verbana currently undergoes a population dispersal. This study also revealed that the lower Danube basin is a hotspot of genetic diversity of H. verbana, where different lineages from the Balkan and Anatolian glacial refugia mixed in the postglacial period. Species Distribution Models (SDMs) indicated that the main ecological variables influencing the current distribution of H. verbana are wetland coverage and elevation. Following the IUCN Red List categories and criteria, the present conservation status of the Mediterranean medicinal leech H. verbana in Romania was assessed as Vulnerable (VU). Our study contributes towards a more refined understanding of the genetic diversity of H. verbana and of the factors that led to its current geographical distribution in Romania and Europe.

Effects of transmission pathways, immunological thresholds, and long-distance dispersal on infectious spread: chronic wasting disease case study

Effects of transmission pathways, immunological thresholds, and long-distance dispersal on infectious spread: chronic wasting disease case study