Evolutionary ecology of dispersal in biodiverse spatially structured systems: what is old and what is new?

Dispersal is a well-recognized driver of ecological and evolutionary dynamics, and simultaneously an evolving trait. Dispersal evolution has traditionally been studied in single-species metapopulations so that it remains unclear how dispersal evolves in metacommunities and metafoodwebs, which are characterized by a multitude of species interactions. Since most natural systems are both species-rich and spatially structured, this knowledge gap should be bridged. Here, we discuss whether knowledge from dispersal evolutionary ecology established in single-species systems holds in metacommunities and metafoodwebs and we highlight generally valid and fundamental principles. Most biotic interactions form the backdrop to the ecological theatre for the evolutionary dispersal play because interactions mediate patterns of fitness expectations across space and time. While this allows for a simple transposition of certain known principles to a multispecies context, other drivers may require more complex transpositions, or might not be transferred. We discuss an important quantitative modulator of dispersal evolution-increased trait dimensionality of biodiverse meta-systems-and an additional driver: co-dispersal. We speculate that scale and selection pressure mismatches owing to co-dispersal, together with increased trait dimensionality, may lead to a slower and more 'diffuse' evolution in biodiverse meta-systems. Open questions and potential consequences in both ecological and evolutionary terms call for more investigation. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Species interactions affect dispersal: a meta-analysis.

Context-dependent dispersal allows organisms to seek and settle in habitats improving their fitness. Despite the importance of species interactions in determining fitness, a quantitative synthesis of how they affect dispersal is lacking. We present a meta-analysis asking (i) whether the interaction experienced and/or perceived by a focal species (detrimental interaction with predators, competitors, parasites or beneficial interaction with resources, hosts, mutualists) affects its dispersal; and (ii) how the species' ecological and biological background affects the direction and strength of this interaction-dependent dispersal. After a systematic search focusing on actively dispersing species, we extracted 397 effect sizes from 118 empirical studies encompassing 221 species pairs; arthropods were best represented, followed by vertebrates, protists and others. Detrimental species interactions increased the focal species' dispersal (adjusted effect: 0.33 [0.06, 0.60]), while beneficial interactions decreased it (-0.55 [-0.92, -0.17]). The effect depended on the dispersal phase, with detrimental interactors having opposite impacts on emigration and transience. Interaction-dependent dispersal was negatively related to species' interaction strength, and depended on the global community composition, with cues of presence having stronger effects than the presence of the interactor and the ecological complexity of the community. Our work demonstrates the importance of interspecific interactions on dispersal plasticity, with consequences for metacommunity dynamics.This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Species interactions and eco-evolutionary dynamics of dispersal: the diversity dependence of dispersal.

Dispersal plays a pivotal role in the eco-evolutionary dynamics of spatially structured populations, communities and ecosystems. As an individual-based trait, dispersal is subject to both plasticity and evolution. Its dependence on conditions and context is well understood within single-species metapopulations. However, species do not exist in isolation; they interact locally through various horizontal and vertical interactions. While the significance of species interactions is recognized for species coexistence and food web functioning, our understanding of their influence on regional dynamics, such as their impact on spatial dynamics in metacommunities and meta-food webs, remains limited. Building upon insights from behavioural and community ecology, we aim to elucidate biodiversity as both a driver and an outcome of connectivity. By synthesizing conceptual, theoretical and empirical contributions from global experts in the field, we seek to explore how a more mechanistic understanding of diversity-dispersal relationships influences the distribution of species in spatially and temporally changing environments. Our findings highlight the importance of explicitly considering interspecific interactions as drivers of dispersal, thus reshaping our understanding of fundamental dynamics including species coexistence and the emergent dynamics of metacommunities and meta-ecosystems. We envision that this initiative will pave the way for advanced forecasting approaches to understanding biodiversity dynamics under the pressures of global change. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

NT-pro-BNP is predictive of morbidity and mortality after pulmonary thromboendarterectomy and is independent of preoperative hemodynamics.

Current predictors of clinical outcomes after pulmonary thromboendarterectomy (PTE) in patients with chronic thromboembolic pulmonary hypertension (CTEPH) are largely limited to preoperative clinical characteristics. N-terminal-pro-brain natriuretic peptide (NT-pro-BNP), a biomarker of right ventricular dysfunction, has not yet been well described as one such predictor. From 2017 to 2021, 816 patients with CTEPH referred to the University of California, San Diego for PTE were reviewed for differences in NT-pro-BNP to predict preoperative characteristics and postoperative outcomes up to 30 days post-PTE. For analysis, NT-pro-BNP was dichotomized to less than/equal to or greater than 1000 pg/mL based on the mean of the study population. Mean NT-pro-BNP was 1095.9 ±1783.4 pg/mL and median was 402.5 pg/mL (interquartile range: 119.5-1410.8). Of the 816 patients included, 250 had NT-pro-BNP > 1000 pg/mL. Those with NT-pro-BNP > 1000 pg/mL were significantly more likely to have worse preoperative functional class (III-IV) and worse preoperative hemodynamics. Patients with NT-pro-BNP > 1000 pg/mL also tended to have more postoperative complications including reperfusion pulmonary edema (22% vs. 5.1%, p < 0.001), airway hemorrhage (8.4% vs. 4.9%, p = 0.075), residual pulmonary hypertension (11.9% vs. 3.1%, p < 0.001), and 30-day mortality (4.8% vs. 1.1%, p = 0.001). Even after adjusting for confounders, patients with NT-pro-BNP > 1000 pg/mL had a 2.48 times higher odds (95% confidence interval: 1.45-4.00) of reaching a combined endpoint that included the above complications. Preoperative NT-pro-BNP > 1000 pg/mL is a strong predictor of more severe preoperative hemodynamics and identifies patients at higher risk for postoperative complications.

Dispersal evolution and eco-evolutionary dynamics in antagonistic species interactions.

Dispersal evolution modifies diverse spatial processes, such as range expansions or biological invasions of single species, but we are currently lacking a realistic vision for metacommunities. Focusing on antagonistic species interactions, we review existing theory of dispersal evolution between natural enemies, and explain how this might be relevant for classic themes in host-parasite evolutionary ecology, namely virulence evolution or local adaptation. Specifically, we highlight the importance of considering the simultaneous (co)evolution of dispersal and interaction traits. Linking such multi-trait evolution with reciprocal demographic and epidemiological feedbacks might change basic predictions about coevolutionary processes and spatial dynamics of interacting species. Future challenges concern the integration of system-specific disease ecology or spatial modifiers, such as spatial network structure or environmental heterogeneity.

A method for synchronized use of EEG and eye tracking in fully immersive VR.

This study explores the synchronization of multimodal physiological data streams, in particular, the integration of electroencephalography (EEG) with a virtual reality (VR) headset featuring eye-tracking capabilities. A potential use case for the synchronized data streams is demonstrated by implementing a hybrid steady-state visually evoked potential (SSVEP) based brain-computer interface (BCI) speller within a fully immersive VR environment. The hardware latency analysis reveals an average offset of 36 ms between EEG and eye-tracking data streams and a mean jitter of 5.76 ms. The study further presents a proof of concept brain-computer interface (BCI) speller in VR, showcasing its potential for real-world applications. The findings highlight the feasibility of combining commercial EEG and VR technologies for neuroscientific research and open new avenues for studying brain activity in ecologically valid VR environments. Future research could focus on refining the synchronization methods and exploring applications in various contexts, such as learning and social interactions.

The second stage of labor.

The second stage of labor extends from complete cervical dilatation to delivery. During this stage, descent and rotation of the presenting part occur as the fetus passively negotiates its passage through the birth canal. Generally, descent begins during the deceleration phase of dilatation as the cervix is drawn upward around the fetal presenting part. The most common means of assessing the normality of the second stage of labor is to measure its duration, but progress can be more meaningfully gauged by measuring the change in fetal station as a function of time. Accurate clinical identification and evaluation of differences in patterns of fetal descent are necessary to assess second stage of labor progress and to make reasoned judgments about the need for intervention. Three distinct graphic abnormalities of the second stage of labor can be identified: protracted descent, arrest of descent, and failure of descent. All abnormalities have a strong association with cephalopelvic disproportion but may also occur in the presence of maternal obesity, uterine infection, excessive sedation, and fetal malpositions. Interpretation of the progress of fetal descent must be made in the context of other clinically discernable events and observations. These include fetal size, position, attitude, and degree of cranial molding and related evaluations of pelvic architecture and capacity to accommodate the fetus, uterine contractility, and fetal well-being. Oxytocin infusion can often resolve an arrest or failure of descent or a protracted descent caused by an inhibitory factor, such as a dense neuraxial block. It should be used only if thorough assessment of fetopelvic relationships reveals a low probability of cephalopelvic disproportion. The value of forced Valsalva pushing, fundal pressure, and routine episiotomy has been questioned. They should be used selectively and where indicated.

A review of combined functional neuroimaging and motion capture for motor rehabilitation.

BACKGROUND: Technological advancements in functional neuroimaging and motion capture have led to the development of novel methods that facilitate the diagnosis and rehabilitation of motor deficits. These advancements allow for the synchronous acquisition and analysis of complex signal streams of neurophysiological data (e.g., EEG, fNIRS) and behavioral data (e.g., motion capture). The fusion of those data streams has the potential to provide new insights into cortical mechanisms during movement, guide the development of rehabilitation practices, and become a tool for assessment and therapy in neurorehabilitation. RESEARCH OBJECTIVE: This paper aims to review the existing literature on the combined use of motion capture and functional neuroimaging in motor rehabilitation. The objective is to understand the diversity and maturity of technological solutions employed and explore the clinical advantages of this multimodal approach. METHODS: This paper reviews literature related to the combined use of functional neuroimaging and motion capture for motor rehabilitation following the PRISMA guidelines. Besides study and participant characteristics, technological aspects of the used systems, signal processing methods, and the nature of multimodal feature synchronization and fusion were extracted. RESULTS: Out of 908 publications, 19 were included in the final review. Basic or translation studies were mainly represented and based predominantly on healthy participants or stroke patients. EEG and mechanical motion capture technologies were most used for biomechanical data acquisition, and their subsequent processing is based mainly on traditional methods. The system synchronization techniques at large were underreported. The fusion of multimodal features mainly supported the identification of movement-related cortical activity, and statistical methods were occasionally employed to examine cortico-kinematic relationships. CONCLUSION: The fusion of motion capture and functional neuroimaging might offer advantages for motor rehabilitation in the future. Besides facilitating the assessment of cognitive processes in real-world settings, it could also improve rehabilitative devices' usability in clinical environments. Further, by better understanding cortico-peripheral coupling, new neuro-rehabilitation methods can be developed, such as personalized proprioceptive training. However, further research is needed to advance our knowledge of cortical-peripheral coupling, evaluate the validity and reliability of multimodal parameters, and enhance user-friendly technologies for clinical adaptation.

Simulating room transfer functions between transducers mounted on audio devices using a modified image source method.

The image source method (ISM) is often used to simulate room acoustics due to its ease of use and computational efficiency. The standard ISM is limited to simulations of room impulse responses between point sources and omnidirectional receivers. In this work, the ISM is extended using spherical harmonic directivity coefficients to include acoustic diffraction effects. These effects occur in practice when transducers are mounted on audio devices of finite spatial extent, e.g., modern smart speakers with loudspeakers and microphones. The proposed method is verified using finite element simulations of various loudspeaker and microphone configurations in a shoebox-shaped room. It is shown that the accuracy of the proposed method is related to the sizes, shapes, number, and positions of the devices inside a room. A simplified version of the proposed method, which can significantly reduce computational effort, is also presented. The proposed method and its simplified version can simulate room transfer functions more accurately than currently available image source methods and can aid the development and evaluation of speech and acoustic signal processing algorithms, including speech enhancement, acoustic scene analysis, and acoustic parameter estimation.

Identification of High-Reliability Regions of Machine Learning Predictions Based on Materials Chemistry.

Progress in the application of machine learning (ML) methods to materials design is hindered by the lack of understanding of the reliability of ML predictions, in particular, for the application of ML to small data sets often found in materials science. Using ML prediction for transparent conductor oxide formation energy and band gap, dilute solute diffusion, and perovskite formation energy, band gap, and lattice parameter as examples, we demonstrate that (1) construction of a convex hull in feature space that encloses accurately predicted systems can be used to identify regions in feature space for which ML predictions are highly reliable; (2) analysis of the systems enclosed by the convex hull can be used to extract physical understanding; and (3) materials that satisfy all well-known chemical and physical principles that make a material physically reasonable are likely to be similar and show strong relationships between the properties of interest and the standard features used in ML. We also show that similar to the composition-structure-property relationships, inclusion in the ML training data set of materials from classes with different chemical properties will not be beneficial for the accuracy of ML prediction and that reliable results likely will be obtained by ML model for narrow classes of similar materials even in the case where the ML model will show large errors on the data set consisting of several classes of materials.

Eco-evolution from deep time to contemporary dynamics: The role of timescales and rate modulators.

Eco-evolutionary dynamics, or eco-evolution for short, are often thought to involve rapid demography (ecology) and equally rapid heritable phenotypic changes (evolution) leading to novel, emergent system behaviours. We argue that this focus on contemporary dynamics is too narrow: Eco-evolution should be extended, first, beyond pure demography to include all environmental dimensions and, second, to include slow eco-evolution which unfolds over thousands or millions of years. This extension allows us to conceptualise biological systems as occupying a two-dimensional time space along axes that capture the speed of ecology and evolution. Using Hutchinson's analogy: Time is the 'theatre' in which ecology and evolution are two interacting 'players'. Eco-evolutionary systems are therefore dynamic: We identify modulators of ecological and evolutionary rates, like temperature or sensitivity to mutation, which can change the speed of ecology and evolution, and hence impact eco-evolution. Environmental change may synchronise the speed of ecology and evolution via these rate modulators, increasing the occurrence of eco-evolution and emergent system behaviours. This represents substantial challenges for prediction, especially in the context of global change. Our perspective attempts to integrate ecology and evolution across disciplines, from gene-regulatory networks to geomorphology and across timescales, from today to deep time.

A stabilizing eco-evolutionary feedback loop in the wild.

There is increasing evidence that evolutionary and ecological processes can operate on the same timescale1,2 (i.e., contemporary time). As such, evolution can be sufficiently rapid to affect ecological processes such as predation or competition. Thus, evolution can influence population, community, and ecosystem-level dynamics. Indeed, studies have now shown that evolutionary dynamics can alter community structure3,4,5,6 and ecosystem function.7,8,9,10 In turn, shifts in ecological dynamics driven by evolution might feed back to affect the evolutionary trajectory of individual species.11 This feedback loop, where evolutionary and ecological changes reciprocally affect one another, is a central tenet of eco-evolutionary dynamics.1,12 However, most work on such dynamics in natural populations has focused on one-way causal associations between ecology and evolution.13 Hence, direct empirical evidence for eco-evolutionary feedback is rare and limited to laboratory or mesocosm experiments.13,14,15,16 Here, we show in the wild that eco-evolutionary dynamics in a plant-feeding arthropod community involve a negative feedback loop. Specifically, adaptation in cryptic coloration in a stick-insect species mediates bird predation, with local maladaptation increasing predation. In turn, the abundance of arthropods is reduced by predation. Here, we experimentally manipulate arthropod abundance to show that these changes at the community level feed back to affect the stick-insect evolution. Specifically, low-arthropod abundance increases the strength of selection on crypsis, increasing local adaptation of stick insects in a negative feedback loop. Our results suggest that eco-evolutionary feedbacks are able to stabilize complex systems by preventing consistent directional change and therefore increasing resilience.

Landscape Structure Affects Metapopulation-Scale Tipping Points.

AbstractEven when environments deteriorate gradually, ecosystems may shift abruptly from one state to another. Such catastrophic shifts are difficult to predict and sometimes to reverse (so-called hysteresis). While well studied in simplified contexts, we lack a general understanding of how catastrophic shifts spread in realistically spatially structured landscapes. For different types of landscape structures, including typical terrestrial modular and riverine dendritic networks, we here investigate landscape-scale stability in metapopulations whose patches can locally exhibit catastrophic shifts. We find that such metapopulations usually exhibit large-scale catastrophic shifts and hysteresis and that the properties of these shifts depend strongly on the metapopulation spatial structure and on the population dispersal rate: an intermediate dispersal rate, a low average degree, or a riverine spatial structure can largely reduce hysteresis size. Our study suggests that large-scale restoration is easier with spatially clustered restoration efforts and in populations characterized by an intermediate dispersal rate.

Outbreaks of dermatopathy caused by Tephrosia noctiflora intoxication in Brazilian cattle.

This study aims to update the knowledge concerning the intoxication by Tephrosia noctiflora in Brazilian cattle herds by reporting new cases of intoxication in lactating cows, their calves and bulls and highlight the epidemiology, clinical signs, pathogenesis, gross, and microscopic lesions. The morbidity and mortality of this intoxication in the farms studied was low. Gross lesions in all affected cattle consisted of dermatitis with hyperpigmentation, crusts, ulceration, erythema, and lichenification in the skin of limbs, ventral abdomen, perianal and perineal areas of lactating calves and adult cattle. Microscopically, the main lesion observed consisted of severe dermatitis with parakeratotic hyperkeratosis, papillated proliferation, and diffuse, accentuated lymphoplasmacytic inflammatory infiltrate in the epidermis and dermis. The presence of skin lesions mainly in the limbs and ventral abdomen of cattle implies the pathogenesis of intoxication is related to a primary contact dermatitis, and the occurrence of similar lesions on the skin of nursing calves reinforces this hypothesis. The putative toxins of T. noctiflora have been thought to be rotenoids. Additional work is needed to define better if these compounds are the main toxin responsible for the dermatopathy observed in these herds.

Online reverberation time and clarity estimation in dynamic acoustic conditions.

Previously proposed methods for estimating acoustic parameters from reverberant, noisy speech signals exhibit insufficient performance under changing acoustic conditions. A data-centric approach is proposed to overcome the limiting assumption of fixed source-receiver transmission paths. The obtained solution significantly enlarges the scope of potential applications for such estimators. The joint estimation of reverberation time RT60 and clarity index C50 in multiple frequency bands is studied with a focus on dynamic acoustic environments. Three different convolutional recurrent neural network architectures are considered to solve the tasks of single-band, multi-band, and multi-task parameter estimation. A comprehensive performance evaluation is provided that highlights the benefits of the proposed approach.

In planta dynamics, transport biases, and endogenous functions of mobile siRNAs in Arabidopsis.

In RNA interference (RNAi), small interfering RNAs (siRNAs) produced from double-stranded RNA guide ARGONAUTE (AGO) proteins to silence sequence-complementary RNA/DNA. RNAi can propagate locally and systemically in plants, but despite recent advances in our understanding of the underlying mechanisms, basic questions remain unaddressed. For instance, RNAi is inferred to diffuse through plasmodesmata (PDs), yet how its dynamics in planta compares with that of established symplastic diffusion markers remains unknown. Also is why select siRNA species, or size classes thereof, are apparently recovered in RNAi recipient tissues, yet only under some experimental settings. Shootward movement of endogenous RNAi in micro-grafted Arabidopsis is also yet to be achieved, while potential endogenous functions of mobile RNAi remain scarcely documented. Here, we show (i) that temporal, localized PD occlusion in source leaves' companion cells (CCs) suffices to abrogate all systemic manifestations of CC-activated mobile transgene silencing, including in sink leaves; (ii) that the presence or absence of specific AGOs in incipient/traversed/recipient tissues likely explains the apparent siRNA length selectivity observed upon vascular movement; (iii) that stress enhancement allows endo-siRNAs of a single inverted repeat (IR) locus to translocate against the shoot-to-root phloem flow; and (iv) that mobile endo-siRNAs generated from this locus have the potential to regulate hundreds of transcripts. Our results close important knowledge gaps, rationalize previously noted inconsistencies between mobile RNAi settings, and provide a framework for mobile endo-siRNA research.

Predicting evolution in experimental range expansions of an aquatic model system.

Predicting range expansion dynamics is an important goal of both fundamental and applied research in conservation and global change biology. However, this is challenging if ecological and evolutionary processes occur on the same time scale. Using the freshwater ciliate Paramecium caudatum, we combined experimental evolution and mathematical modeling to assess the predictability of evolutionary change during range expansions. In the experiment, we followed ecological dynamics and trait evolution in independently replicated microcosm populations in range core and front treatments, where episodes of natural dispersal alternated with periods of population growth. These eco-evolutionary conditions were recreated in a predictive mathematical model, parametrized with dispersal and growth data of the 20 founder strains in the experiment. We found that short-term evolution was driven by selection for increased dispersal in the front treatment and general selection for higher growth rates in all treatments. There was a good quantitative match between predicted and observed trait changes. Phenotypic divergence was further mirrored by genetic divergence between range core and front treatments. In each treatment, we found the repeated fixation of the same cytochrome c oxidase I (COI) marker genotype, carried by strains that also were the most likely winners in our model. Long-term evolution in the experimental range front lines resulted in the emergence of a dispersal syndrome, namely a competition-colonization trade-off. Altogether, both model and experiment highlight the potential importance of dispersal evolution as a driver of range expansions. Thus, evolution at range fronts may follow predictable trajectories, at least for simple scenarios, and predicting these dynamics may be possible from knowledge of few key parameters.

Two congruent cues are better than one: Impact of ITD-ILD combinations on reaction time for sound lateralization.

This letter presents a reaction time analysis of a sound lateralization test. Sounds from various directions were synthesized using interaural time-level difference (ITD-ILD) combinations, and human subjects performed left/right detection. Stimuli from the sides yielded quicker reactions and better class accuracy than from the front. Congruent ITD-ILD cues significantly improved both metrics. For opposing ITD-ILD cues, subjects' choices were mostly driven by the ITD, and the responses were significantly slower. The findings, obtained with an easily accessible methodology, corroborate the integrated processing of the binaural cues and promote the use of multiple congruent binaural cues in headphone reproduction.

Early Biliary Decompression Reduces Morbidity but Not Mortality in Acute Ascending Cholangitis.

Background Acute ascending cholangitis is a life-threatening infection due to biliary obstruction. Decompression via endoscopic retrograde cholangiography (ERC) or interventional radiologic (IR) drainage controls the source of the sepsis. Numerous studies have been published with conflicting data on whether earlier drainage affects morbidity and mortality. We sought to publish our experience at two Las Vegas community hospitals. Methods After IRB approval, over 4000 inpatient non-elective ERCs were analyzed between 2010 and 2019. Six-hundred and twenty-five patients met the 2018 Tokyo criteria for a "definitive diagnosis" of acute ascending cholangitis. A univariate and multivariate analysis was conducted to identify factors significantly associated with length of stay and mortality. Results On univariate analysis, patients who had drainage conducted within 24 hours had significantly shorter lengths of stay (p = 0.0012 95% CI [-88.1 to -21.8 hrs]), higher mean diastolic blood pressure (p=0.0029 95% CI [1.03 to 5.01 mm Hg]), and lower mean maximum temperature (p=0.0001 95% CI [-0.842 to -0.382 oC]) when compared to patients who underwent decompression more than 24 hours after admission. There were no statistically significant differences in mortality between patients who underwent decompression within 24 hours of admission versus patients who underwent decompression beyond 24 hours of admission. On multivariate analysis, earlier decompression reduced the length of stay for patients with mild (p<0.0001), moderate (p<0.0001), and severe cholangitis (p=0.0023). Mortality was significantly associated with the worsening severity of the cholangitis (moderate [p=0.0001] and severe [p<0.0001], but not mild disease) and the use of vasopressors. Conclusions Timely biliary decompression within 24 hours of admission significantly reduces the length of stay, pyrexia, and hemodynamic abnormalities. In addition, our data corroborate the 2018 Tokyo guidelines that correlate the severity of cholangitis with mortality.

Experimental evolution of dispersal: Unifying theory, experiments and natural systems.

Dispersal is a central life history trait that affects the ecological and evolutionary dynamics of populations and communities. The recent use of experimental evolution for the study of dispersal is a promising avenue for demonstrating valuable proofs of concept, bringing insight into alternative dispersal strategies and trade-offs, and testing the repeatability of evolutionary outcomes. Practical constraints restrict experimental evolution studies of dispersal to a set of typically small, short-lived organisms reared in artificial laboratory conditions. Here, we argue that despite these restrictions, inferences from these studies can reinforce links between theoretical predictions and empirical observations and advance our understanding of the eco-evolutionary consequences of dispersal. We illustrate how applying an integrative framework of theory, experimental evolution and natural systems can improve our understanding of dispersal evolution under more complex and realistic biological scenarios, such as the role of biotic interactions and complex dispersal syndromes.