Beyond connectivity: how the structure of dispersal influences metacommunity dynamics

Dispersal within metacommunities can play a major role in species persistence by promoting asynchrony between communities. Understanding this role is crucial both for explaining species coexistence and managing landscapes that are increasingly fragmented by human activities. Here, we demonstrate that spatial patterning of dispersal connections can drastically alter both the tendency toward asynchrony and the effect of asynchrony on metacommunity dynamics commonly used to infer the potential for persistence. We also demonstrate that changes in dispersal connections in strictly homogeneous predator-prey metacommunities can generate an extremely rich variety of dynamics even when previously investigated properties of connectivity such as the magnitude and distribution of dispersal among patches are held constant. Furthermore, the dynamics we observe depend strongly on initial conditions. Our results illustrate the effectiveness of measures of spatial structure for predicting asynchrony and its effects on community dynamics, providing a deeper understanding of the relationship between spatial structure and species persistence in metacommunities.     

The highs and lows of scientific conferences

What are the main characteristics of scientific conferences and what distinguishes the successful meetings from the less successful? Here, semi-seriously, I present a set of observations and suggestions that are organized into categories (such as big versus little conferences and long versus short conferences) and, for each category, I award the new meeting Oscars - the Georges.     

From dispersal to landscapes: progress in the understanding of population dynamics

The development of our understanding of population dynamics over the past 50 years is reviewed from a personal perspective. An early emphasis on population vital rates was superceded by recognition of the importance of the specific community context of focal populations, and most recently has in turn been enriched by a landscape perspective. Certain basic principles are outlined including the value of a systems context for population analyses, the power of a dual mechanistic and contextual perspective, and the inevitability of density control in a finite biosphere. Numbers are determined by the balance of two complex parameters:p — the per capita growth promoting (enhancing) forces, ands — the per capita growth suppressing forces. Multiple factor explanations of demographic behavior are therefore to be expected, as well as temporal and spatial variations in them. An appreciation for the potential role of dispersal as a population vital rate led to the development of metapopulation theory. A renewed understanding of the role of community context in population dynamics provoked the realization that a multi-factor approach was required. This in turn allowed us to reconcile the reality of local demographic complexity with global generalizations. Finally, the introduction of landscape ecology into demographic thinking added many new insights. It is now appreciated that a spatially explicit mosaic of habitat patches, edge effects, corridors, and even the proportion of favorable to marginal habitats can all be critically important factors in influencing population dynamics.     

The highs and lows of theoretical interpretation in animal-metacognition research

Humans feel uncertain. They know when they do not know. These feelings and the responses to them ground the research literature on metacognition. It is a natural question whether animals share this cognitive capacity, and thus animal metacognition has become an influential research area within comparative psychology. Researchers have explored this question by testing many species using perception and memory paradigms. There is an emerging consensus that animals share functional parallels with humans' conscious metacognition. Of course, this research area poses difficult issues of scientific inference. How firmly should we hold the line in insisting that animals' performances are low-level and associative? How high should we set the bar for concluding that animals share metacognitive capacities with humans? This area offers a constructive case study for considering theoretical problems that often confront comparative psychologists. The authors present this case study and address diverse issues of scientific judgement and interpretation within comparative psychology.     

The highs and lows of plant life: temperature and light interactions in development

Plants must constantly respond to changes in the environment whilst maintaining developmental and growth processes if they are to survive into the next generation. A complex network of signals from temperature and light must correctly converge to achieve successful development, through vegetative to reproductive growth. Temperature can be thought of as an environmental factor that provides both 'inductive' and 'maintenance' signals in development. It can stimulate developmental processes such as seed dormancy release, germination and vernalization. However, when temperature is not regarded as inductive, an accommodating network of genes work in concert to ensure growth responses occur regardless of fluctuating microclimate conditions. Many of the temperature-regulated developmental pathways are intimately linked with light signaling. For example, light-temperature interactions are major determinants in the timing of reproductive development. Indeed, the ability to process and react to complex environmental cues is crucial for both normal and adaptive development in a changing environment. These responses are frequently mediated by manipulating the phytohormone network, which serves as a powerful, yet adaptable controller of development. This paper illustrates the influential role temperature perception plays throughout plant development and the close interaction between temperature, light and hormone signaling.     

The role of rapid dispersal in the population dynamics of competition

A dynamical equation for the spatial distribution of competing species that contains a growth term and a dispersal term is analyzed under the condition that the dispersal rate is sufficiently rapid compared to the growth rate. With this assumption, the equation becomes analogous to the niche-partitioning theory of MacArthur and Levins (1967, Amer. Natur. 101, 377–385) and thus provides a link between the theory of local niche partitioning and the theory of regional habitat segregation. The formulation is applied to a two species system consisting of a specialist and a generalist competing with each other in an environment composed of two different habitats. The analysis shows that dispersal due to directed movement toward a favorable habitat and density dependent random movement both facilitate coexistence.     

The dynamics of a discrete population model with threshold

The dynamics of the discrete, scalar population model x_{k + 1} = ax²_k(1 – x_k) are investigated. In addition to density dependence, which has been studied previously by many, this equation models the threshold phenomenon. Some similarities to and differences from previous models are observed. In particular, for large a values this model exhibits chaos which is restricted to a nowhere dense Cantor set of measure 0. In order to explain this, a piecewise linear simplification of the model is considered. Other models exhibiting similar dynamics are also mentioned.     

Asymmetric dispersal and survival indicate population sources for grassland butterflies in agricultural landscapes

We tested the hypothesis that populations in small habitat fragments remaining in agricultural landscapes are maintained by repeated immigration, using three grassland butterflies ( Aphantopus hyperantus , Coenonympha pamphilus and Maniola jurtina ). Transect counts in 12 matched sets of semi-natural pastures, and linear habitat elements proximate and isolated from the pastures showed that population densities of M.  jurtina and C.  pamphilus were significantly higher in pastures and in linear habitats adjacent to these than in isolated linear elements. A mark-recapture study in a 2×2 km landscape indicated that individuals of all three species are able to reach even the isolated linear elements situated at least 1 km from the grasslands. For two of the species, A.  hyperantus and C.  pamphilus , analysis of the mark-recapture data revealed higher daily local survival rates in the semi-natural pastures and more individuals dispersing from pastures to linear habitat elements. The proportion of old compared to young individuals of C.  pamphilus and M.  jurtina were significantly higher in linear elements than in semi-natural pastures, which suggests that butterflies emerging in pastures subsequently dispersed to the linear elements. In combination, these results suggest that semi-natural pastures act as population sources, from which adult butterflies disperse to surrounding linear elements. Hence, preservation of the remaining fragments of semi-natural grassland is necessary to keep the present butterfly abundance in the surrounding agricultural landscape.     

Repeat proliferation and partial endoreplication jointly shape the patterns of genome size evolution in orchids

Although the evolutionary drivers of genome size change are known, the general patterns and mechanisms of plant genome size evolution are yet to be established. Here we aim to assess the relative importance of proliferation of repetitive DNA, chromosomal variation (including polyploidy), and the type of endoreplication for genome size evolution of the Pleurothallidinae, the most species-rich orchid lineage. Phylogenetic relationships between 341 Pleurothallidinae representatives were refined using a target enrichment hybrid capture combined with high-throughput sequencing approach. Genome size and the type of endoreplication were assessed using flow cytometry supplemented with karyological analysis and low-coverage Illumina sequencing for repeatome analysis on a subset of samples. Data were analyzed using phylogeny-based models. Genome size diversity (0.2–5.1 Gbp) was mostly independent of profound chromosome count variation (2n = 12–90) but tightly linked with the overall content of repetitive DNA elements. Species with partial endoreplication (PE) had significantly greater genome sizes, and genomic repeat content was tightly correlated with the size of the non-endoreplicated part of the genome. In PE species, repetitive DNA is preferentially accumulated in the non-endoreplicated parts of their genomes. Our results demonstrate that proliferation of repetitive DNA elements and PE together shape the patterns of genome size diversity in orchids.     

How propagule size and environmental suitability jointly determine establishment success: a test using dung beetle introductions

Both the size of founding populations (propagule size) and environmental suitability are known to influence whether a species newly introduced to a location will establish a self-sustaining population. However, these two factors do not operate independently: it is the interaction between propagule size and environmental suitability that determines the probability an introduced population will establish. Here I use the example of dung beetle introductions to Australia to illustrate the importance of this interaction. I first describe equations that model establishment success jointly as a function of propagule size and environmental suitability. I then show how these equations provide insight into the different outcomes observed in two dung beetle species widely introduced to Australia. In one species, variation in propagule size had relatively little influence on establishment success due to large variation in environmental suitability, leading to an essentially bimodal outcome: sites were either very suitable for establishment and introductions succeeded, or sites were unsuitable and introductions failed regardless of propagule size. For the second species, there was much less variation among locations in environmental suitability, leading to propagule size having a strong influence on establishment success. These examples highlight how the interplay between environmental suitability and founding population size is central to determining the probability an introduced species will establish.     

The global dynamics of a discrete nonlinear hierarchical population system

This paper is concerned with the global dynamics of a hierarchical population model,in which the fertility of an individual depends on the total number of higher-ranking members.We investigate the stability of equilibria,nonexistence of periodic orbits and the persistence of the population by means of eigenvalues,Lyapunov function,and several results in discrete dynamical systems.Our work demonstrates that the reproductive number governs the evolution of the population.Besides the theoretical results,some numerical experiments are also presented.     

Prospecting and dispersal: their eco-evolutionary dynamics and implications for population patterns

Dispersal is not a blind process, and evidence is accumulating that individual dispersal strategies are informed in most, if not all, organisms. The acquisition and use of information are traits that may evolve across space and time as a function of the balance between costs and benefits of informed dispersal. If information is available, individuals can potentially use it in making better decisions, thereby increasing their fitness. However, prospecting for and using information probably entail costs that may constrain the evolution of informed dispersal, potentially with population-level consequences. By using individual-based, spatially explicit simulations, we detected clear coevolutionary dynamics between prospecting and dispersal movement strategies that differed in sign and magnitude depending on their respective costs. More specifically, we found that informed dispersal strategies evolve when the costs of information acquisition during prospecting are low but only if there are mortality costs associated with dispersal movements. That is, selection favours informed dispersal strategies when the acquisition and use processes themselves were not too expensive. When non-informed dispersal strategies evolve, they do so jointly with the evolution of long dispersal distance because this maximizes the sampling area. In some cases, selection produces dispersal rules different from those that would be ‘optimal’ (i.e. the best possible population performance—in our context quantitatively measured as population density and patch occupancy—among all possible individual movement rules) for the population. That is, on the one hand, informed dispersal strategies led to population performance below its highest possible level. On the other hand, un- and poorly informed individuals nearly optimized population performance, both in terms of density and patch occupancy.     

Modeling bird species distribution change in fire prone Mediterranean landscapes: incorporating species dispersal and landscape dynamics

Species distribution models (SDMs) have traditionally been founded on the assumption that species distributions are in equilibrium with environmental conditions and that these species–environment relationships can be used to estimate species responses to environmental changes. Insight into the validity of this assumption can be obtained from comparing the performance of correlative species distribution models with more complex hybrid approaches, i.e. correlative and process‐based models that explicitly include ecological processes, thereby accounting for mismatches between habitat suitability and species occupancy patterns. Here we compared the ability of correlative SDMs and hybrid models, which can accommodate non‐equilibrium situations arising from dispersal constraints, to reproduce the distribution dynamics of the ortolan bunting Emberiza hortulana in highly dynamic, early successional, fire driven Mediterranean landscapes. Whereas, habitat availability was derived from a correlative statistical SDM, occupancy was modeled using a hybrid approach combining a grid‐based, spatially‐explicit population model that explicitly included bird dispersal with the correlative model. We compared species occupancy patterns under the equilibrium assumption and different scenarios of species dispersal capabilities. To evaluate the predictive capability of the different models, we used independent species data collected in areas affected to different degree by fires. In accordance with the view that disturbance leads to a disparity between the suitable habitat and the occupancy patterns of the ortolan bunting, our results indicated that hybrid modeling approaches were superior to correlative models in predicting species spatial dynamics. Furthermore, hybrid models that incorporated short dispersal distances were more likely to reproduce the observed changes in ortolan bunting distribution patterns, suggesting that dispersal plays a key role in limiting the colonization of recently burnt areas. We conclude that SDMs used in a dynamic context can be significantly improved by using combined hybrid modeling approaches that explicitly account for interactions between key ecological constraints such as dispersal and habitat suitability that drive species response to environmental changes.     

Evolution of reduced dispersal mortality and 'fat-tailed' dispersal kernels in autocorrelated landscapes

Models describing the evolution of dispersal strategies have mostly focused on the evolution of dispersal rates. Taking trees as a model for organisms with undirected, passive dispersal, we have developed an individual-based, spatially explicit simulation tool to investigate the evolution of the dispersal kernel, P(r), and its resulting cumulative seed-density distribution, D(r). Simulations were run on a variety of fractal landscapes differing in the fraction of suitable habitat and the spatial autocorrelation. Starting from a uniform D(r), evolution led to an increase in the fraction of seeds staying in the home cell, a reduction of the dispersal mortality (arrival in unsuitable habitat), and the evolution of 'fat-tailed' D(r) in autocorrelated landscapes and approximately uniform D(r) in random landscapes. The evolutionary process was characterized by long periods of stasis with a few bouts of rapid change in the dispersal rate.     

How Nemo finds home: the neuroecology of dispersal and of population connectivity in larvae of marine fishes

Nearly all demersal teleost marine fishes have pelagic larval stages lasting from several days to several weeks, during which time they are subject to dispersal. Fish larvae have considerable swimming abilities, and swim in an oriented manner in the sea. Thus, they can influence their dispersal and thereby, the connectivity of their populations. However, the sensory cues marine fish larvae use for orientation in the pelagic environment remain unclear. We review current understanding of these cues and how sensory abilities of larvae develop and are used to achieve orientation with particular emphasis on coral-reef fishes. The use of sound is best understood; it travels well underwater with little attenuation, and is current-independent but location-dependent, so species that primarily utilize sound for orientation will have location-dependent orientation. Larvae of many species and families can hear over a range of ~100-1000 Hz, and can distinguish among sounds. They can localize sources of sounds, but the means by which they do so is unclear. Larvae can hear during much of their pelagic larval phase, and ontogenetically, hearing sensitivity, and frequency range improve dramatically. Species differ in sensitivity to sound and in the rate of improvement in hearing during ontogeny. Due to large differences among-species within families, no significant differences in hearing sensitivity among families have been identified. Thus, distances over which larvae can detect a given sound vary among species and greatly increase ontogenetically. Olfactory cues are current-dependent and location-dependent, so species that primarily utilize olfactory cues will have location-dependent orientation, but must be able to swim upstream to locate sources of odor. Larvae can detect odors (e.g., predators, conspecifics), during most of their pelagic phase, and at least on small scales, can localize sources of odors in shallow water, although whether they can do this in pelagic environments is unknown. Little is known of the ontogeny of olfactory ability or the range over which larvae can localize sources of odors. Imprinting on an odor has been shown in one species of reef-fish. Celestial cues are current- and location-independent, so species that primarily utilize them will have location-independent orientation that can apply over broad scales. Use of sun compass or polarized light for orientation by fish larvae is implied by some behaviors, but has not been proven. Use of neither magnetic fields nor direction of waves for orientation has been shown in marine fish larvae. We highlight research priorities in this area.