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  Subjects -> ENVIRONMENTAL STUDIES (Total: 777 journals)
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ENVIRONMENTAL STUDIES (706 journals)

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Journal Cover Theoretical Ecology
  [SJR: 1.255]   [H-I: 19]   [12 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1874-1746 - ISSN (Online) 1874-1738
   Published by Springer-Verlag Homepage  [2354 journals]
  • A navigational guide to variable fitness: common methods of analysis,
           where they break down, and what you can do instead
    • Authors: Robin E. Snyder
      Pages: 375 - 389
      Abstract: Our methods for analyzing stochastic fitness are mostly approximations, and the assumptions behind these approximations are not always well understood. Furthermore, many of these approximations break down when fitness variance is high. This review covers geometric mean growth, diffusion approximations, and Markov processes. It discusses where each is appropriate, the conditions under which they break down, and their advantages and disadvantages, with special attention to the case of high fitness variance. A model of sessile and site-attached coastal species is used as a running example, and fully worked calculations and code are provided. Summary: The logarithm of geometric mean growth is usually only appropriate when (a) an invader growth rate is needed and (b) fitness variability is driven by environmental fluctuations. The usual approximation breaks down when fitness variance is high. Diffusion approximations can provide a reasonable guide to the expected change in frequency over a time step if expected fitnesses and fitness variances are appropriately scaled by the average expected fitness. Diffusion approximations can perform less well for fixation probabilities, especially since further approximations may be required. Fixation probabilities can be calculated exactly using a Markov process, regardless of how large fitness variance is, although an analytic expression is frequently not possible. If an analytic expression is desired, it may be worth using a diffusion approximation and checking it with a Markov process calculation.
      PubDate: 2017-12-01
      DOI: 10.1007/s12080-017-0337-0
      Issue No: Vol. 10, No. 4 (2017)
       
  • A theoretical basis for the study of predatory syrphid fly ecology
    • Authors: Paul Glaum
      Pages: 391 - 402
      Abstract: Predacious syrphid fly species, also known as flower flies or hover flies, are cosmopolitan diptera that play two important ecological roles: predator and pollinator. In decades past, syrphid flies were studied by agricultural researchers due to their larvae’s ability to function as a biological control agent. In recent years, the global decline in both honey bees and various important wild bee species has led ecological researchers to investigate the role of syrphid fly pollination in both natural systems and agriculture. While these two roles have often been considered separately, they are rarely considered together in single studies. Syrphid fly population fluctuations in natural and agricultural systems are understudied, prompting calls for further study into the fundamental drivers of population dynamics of syrphid communities. In order to develop a deeper understanding of the fundamental dynamics of syrphid ecology, the present study offers a community model where both syrphid predation and pollination are incorporated into a single dynamic model. Using populations of predacious syrphid flies, herbivorous insects, and a shared resource flowering plant, the model is used to investigate community dynamics and persistence across different levels of plant reproductive dependence on syrphid pollination. Results indicate distinct levels of community viability across different pollination relationships as well as a tendency toward chaotic dynamics inherent to the trophic interactions of the community.
      PubDate: 2017-12-01
      DOI: 10.1007/s12080-017-0336-1
      Issue No: Vol. 10, No. 4 (2017)
       
  • Effects of long-range taxis and population pressure on the range expansion
           of invasive species in heterogeneous environments
    • Authors: Kohkichi Kawasaki; Nanako Shigesada; Mamiko Iinuma
      Pages: 269 - 286
      Abstract: We consider a new model for biological invasions in periodic patchy environments, in which long-range taxis and population pressure are incorporated in the framework of reaction-diffusion-advection equations. We assume that long-range taxis is induced by a weighted integral of stimuli within a certain sensing range. Population pressure is incorporated in the diffusion coefficient that linearly increases with population density. We first analyze the model in the absence of population pressure and demonstrate how the sensing length of long-range taxis influences the range expansion pattern of invasive species and its rate of spread. The effects of population pressure are examined for both homogeneous and periodic patchy environments. For the homogeneous environment, an exact and explicit traveling wave solution and the spreading speed are obtained. For the periodic patchy environment, we find numerically that a population starting from any localized distribution evolves to a traveling periodic wave if the null solution of the RDA equation is locally unstable, and that the traveling wave speed significantly increases with increasing population pressure. Furthermore, the population pressure and taxis intensity synergistically enhance the spreading speed when they are increased together.
      PubDate: 2017-09-01
      DOI: 10.1007/s12080-017-0328-1
      Issue No: Vol. 10, No. 3 (2017)
       
  • Barnacles vs bullies: modelling biocontrol of the invasive European green
           crab using a castrating barnacle parasite
    • Authors: Andrew W. Bateman; Andreas Buttenschön; Kelley D. Erickson; Nathan G. Marculis
      Pages: 305 - 318
      Abstract: Invasive species raise concern around the globe, and much empirical and theoretical research effort has been devoted to their management. Integrodifference equations are theoretical tools that have been used to understand the spatiotemporal process of a species invasion, with the potential to yield insight into the possible biological control measures. We develop a system of integrodifference equations to explore the potential release of a castrating barnacle parasite Sacculina carcini to control spread and abundance of an invasive species, Carcinus maenas, the European green crab. We find that the parasite does not completely eradicate the green crab population, but has the potential to reduce its density. Our model suggests that the crab population is likely to outrun the spread of the parasite, causing two waves of invasion travelling at different speeds. By performing a sensitivity analysis, we investigate the effects of the demographic parameters on the speed of invasion. To conclude, we discuss the predicted outcomes for the European green crab, and other non-target hosts, of using the castrating barnacle as a biocontrol agent.
      PubDate: 2017-09-01
      DOI: 10.1007/s12080-017-0332-5
      Issue No: Vol. 10, No. 3 (2017)
       
  • Beyond connectivity: how the structure of dispersal influences
           metacommunity dynamics
    • Authors: Sean M. Hayes; Kurt E. Anderson
      Abstract: 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.
      PubDate: 2017-11-17
      DOI: 10.1007/s12080-017-0355-y
       
  • Landscape configuration drives persistent spatial patterns of occupant
           distributions
    • Authors: Elizabeth A. Hamman; Scott A. McKinley; Adrian C. Stier; Craig W. Osenberg
      Abstract: Variation in the density of organisms among habitat patches is often attributed to variation in inherent patch properties. For example, higher quality patches might have higher densities because they attract more colonists or confer better post-colonization survival. However, variation in occupant density can also be driven by landscape configuration if neighboring patches draw potential colonists away from the focal habitat (a phenomenon we call propagule redirection). Here, we develop and analyze a stochastic model to quantify the role of landscape configuration and propagule redirection on occupant density patterns. We model a system with a dispersive larval stage and a sedentary adult stage. The model includes sensing and decision-making in the colonization stage and density-dependent mortality (a proxy for patch quality) in the post-colonization stage. We demonstrate that spatial variation in colonization is retained when the supply of colonists is not too high, post-colonization density-dependent survival is not too strong, and colonization events are not too frequent. Using a reef fish system, we show that the spatial variation produced by propagule redirection is comparable to spatial variation expected when patch quality varies. Thus, variation in density arising from the spatial patterning of otherwise identical habitat can play an important role in shaping long-term spatial patterns of organisms occupying patchy habitats. Propagule redirection is a potentially powerful mechanism by which landscape configuration can drive variation in occupant densities, and may therefore offer new insights into how populations may shift as landscapes change in response to natural and anthropogenic forces.
      PubDate: 2017-11-16
      DOI: 10.1007/s12080-017-0352-1
       
  • Dynamic choices are most accurate in small groups
    • Authors: Julián Vicente-Page; Alfonso Pérez-Escudero; Gonzalo G. de Polavieja
      Abstract: According to the classic results of Galton and Condorcet, as well as in modern decision-making models, accuracy in groups increases with group size. However, these studies do not consider the naturally occurring situation in which individuals dynamically re-evaluate their decision with a possible change of opinion. The dynamics of re-evaluation in groups are very different to individual re-evaluation because individuals influence the group and the group influences the individual. We find that individual accuracy in a group is higher when individuals re-evaluate because all members have more access to social information, while in single decisions, those deciding first have less. This improvement is smaller in large groups as in this case errors can cascade across the members of the group before re-evaluation can correct them. The net result is a maximal accuracy at a small group size. We also analyzed the case in which individuals are influenced only by a small number of the other individuals. In this case, cascading errors affect the interacting subgroups but are very unlikely to reach the whole group. This results in a local optimum at a small group size but also an optimum at a very large size. We thus suggest that re-evaluation dynamics can make small and very large groups optimal. Also, features that may be seen as limitations, like an influence from only a small number of individuals, may turn to be beneficial when considering local animal interactions, here filtering out cascading of errors in the group when reconsideration dynamics takes place.
      PubDate: 2017-10-30
      DOI: 10.1007/s12080-017-0349-9
       
  • Coexistence and displacement in consumer-resource systems with local and
           shared resources
    • Authors: Victoria M. Hunt; Joel S. Brown
      Abstract: Competition for local and shared resources is widespread. For example, colonial waterbirds consume local prey in the immediate vicinity of their colony, as well as shared prey across multiple colonies. However, there is little understanding of conditions facilitating coexistence vs. displacement in such systems. Extending traditional models based on type I and type II functional responses, we simulate consumer-resource systems in which resources are “substitutable,” “essential,” or “complementary.” It is shown that when resources are complementary or essential, a small increase in carrying capacity or decrease in handling time of a local resource may displace a spatially separate consumer species, even when the effect on shared resources is small. This work underscores the importance of determining both the nature of resource competition (substitutable, essential, or complementary) and appropriate scale-dependencies when studying metacommunities. We discuss model applicability to complex systems, e.g., urban wildlife that consume natural and anthropogenic resources which may displace rural competitors by depleting shared prey.
      PubDate: 2017-10-24
      DOI: 10.1007/s12080-017-0350-3
       
  • Generalizing matrix structure affects the identification of least-cost
           paths and patch connectivity
    • Authors: Shantel J. Koenig; Darren J. Bender
      Abstract: Understanding and assessing landscape connectivity is often a primary goal when studying patchy or spatially structured populations. It is commonly accepted that the matrix plays a role in determining connectivity; however, it is not clear how the process of assessing connectivity is impacted by different ways in which the matrix may be represented, particularly if matrix structure is generalized to expedite analysis. We conducted a controlled experiment using computer simulations to evaluate the impact of increasing levels of matrix generalization on connectivity assessment using a constant arrangement of habitat patches. We varied matrix generalization for six simulated landscape patterns by adjusting the number of classes and level of pattern grain in 16 ways to yield sets of landscapes for which the matrix ranged from not generalized (i.e., heterogeneous) to completely generalized (i.e., homogeneous) while habitat placement was held constant. Least-cost paths were calculated for each landscape, and a spatial interaction model (SIM) was implemented to model the counts of patch inflows (immigration) and pairwise exchange. Applying a SIM allowed us to generate absolute outputs and explicitly compare the effect of changes to matrix generalization on connectivity. We found that both assessment of connections (i.e., measured distance and spatial delineation of least-cost paths) and patch inflows/pairwise exchange were highly sensitive to matrix generalization and that effects were inconsistent and unpredictable across the range of matrix representations, especially when estimating connectivity for individual patches. We conclude that matrix pattern may have an underappreciated effect on connectivity and that least-cost path delineation and connectivity assessment may be very sensitive to generalizations of the matrix. We suggest that sensitivity analysis of the matrix representation should be performed when conducting connectivity analyses.
      PubDate: 2017-10-23
      DOI: 10.1007/s12080-017-0351-2
       
  • The dispersal success and persistence of populations with asymmetric
           dispersal
    • Authors: D. Scott Rinnan
      Abstract: Asymmetric dispersal is a common trait among populations, often attributed to heterogeneity and stochasticity in both environment and demography. The cumulative effects of population dispersal in space and time have been described with some success by Van Kirk and Lewis’s average dispersal success approximation (Bull Math Biol 59(1): 107–137 1997), average dispersal success approximation, but this approximation has been demonstrated to perform poorly when applied to asymmetric dispersal. Here we provide a comparison of different characterizations of dispersal success and demonstrate how to capture the effects of asymmetric dispersal. We apply these different methods to a variety of integrodifference equation population models with asymmetric dispersal, and examine the methods’ effectiveness in approximating key ecological traits of the models, such as the critical patch size and the critical speed of climate change for population persistence.
      PubDate: 2017-10-16
      DOI: 10.1007/s12080-017-0348-x
       
  • Do yearly temperature cycles reduce species richness' Insights from
           calanoid copepods
    • Authors: Harshana Rajakaruna; Mark Lewis
      Abstract: The metabolic theory of ecology (MTE) has explained the taxonomic richness of ectothermic species as an inverse function of habitat mean temperature. Extending this theory, we show that yearly temperature cycles reduce metabolic rates of taxa having short generation times. This reduction is due to Jensen’s inequality, which results from a nonlinear dependency of metabolic rate of organisms on temperature. It leads to a prediction that relatively lower species richness is found in habitats with larger amplitudes of yearly temperature cycles where mean temperatures and other conditions are similar. We show that metabolically driven generation time of a taxon also relates functionally to species richness, and similarly, its yearly cycles reduce richness. We test these hypotheses on marine calanoid copepods with 46,377 records of data collected by scientific cruise surveys in Mediterranean regions, across which the temperature amplitudes vary dramatically. We test both bio-energetic and phenomenological effects of temperature cycles on richness in 86 1° × 1° latitudinal and longitudinal spatial units. The models incorporated the effect of both periodic fluctuations and mean temperature explained 21.6% more variation in the data, with lower AIC, compared to models incorporated only the mean temperature. The study also gives insight into the basis of energetic-equivalence rule in MTE determining richness, which can be governed by generation time of taxon. The results of this study lead to the proposition that amplitude of yearly temperature cycles may contribute to both the longitudinal and the latitudinal differences in species richness and show how the metabolic theory can explain macro-ecological patterns arising from yearly temperature cycles.
      PubDate: 2017-10-12
      DOI: 10.1007/s12080-017-0347-y
       
  • Dynamics from a predator-prey-quarry-resource-scavenger model
    • Authors: Joanneke E. Jansen; Robert A. Van Gorder
      Abstract: Allochthonous resources can be found in many foodwebs and can influence both the structure and stability of an ecosystem. In order to better understand the role of how allochthonous resources are transferred as quarry from one predator-prey system to another, we propose a predator-prey-quarry-resource-scavenger (PPQRS) model, which is an extension of an existing model for quarry-resource-scavenger (a predator-prey-subsidy (PPS) model). Instead of taking the allochthonous resource input rate as a constant, as has been done in previous theoretical work, we explicitly incorporated the underlying predator-prey relation responsible for the input of quarry. The most profound differences between PPS and PPQRS system are found when the predator-prey system has limit cycles, resulting in a periodic rather than constant influx of quarry (the allochthonous resource) into the scavenger-resource interactions. This suggests that the way in which allochthonous resources are input into a predator-prey system can have a strong influence over the population dynamics. In order to understand the role of seasonality, we incorporated non-autonomous terms and showed that these terms can either stabilize or destabilize the dynamics, depending on the parameter regime. We also considered the influence of spatial motion (via diffusion) by constructing a continuum partial differential equation (PDE) model over space. We determine when such spatial dynamics essentially give the same information as the ordinary differential equation (ODE) system, versus other cases where there are strong spatial differences (such as spatial pattern formation) in the populations. In situations where increasing the carrying capacity in the ODE model drives the amplitude of the oscillations up, we found that a large carrying capacity in the PDE model results in a very small variation in average population size, showing that spatial diffusion is stabilizing for the PPQRS model.
      PubDate: 2017-09-14
      DOI: 10.1007/s12080-017-0346-z
       
  • Application of input to state stability to reservoir models
    • Authors: Markus Müller; Carlos A. Sierra
      Abstract: Reservoir models play an important role in representing fluxes of matter and energy in ecological systems and are the basis of most models in biogeochemistry. These models are commonly used to study the effects of environmental change on the cycling of biogeochemical elements and to predict potential transitions of ecosystems to alternative states. To study critical regime changes of time-dependent, externally forced biogeochemical systems, we analyze the behavior of reservoir models typical for element cycling (e.g., terrestrial carbon cycle) with respect to time-varying signals by applying the mathematical concept of input to state stability (ISS). In particular, we discuss ISS as a generalization of preceding stability notions for non-autonomous, non-linear reservoir models represented by systems of ordinary differential equations explicitly dependent on time and a time-varying input signal. We also show how ISS enhances existing stability concepts, previously only available for linear time variant (LTV) systems, to a tool applicable also in the non-linear case.
      PubDate: 2017-08-29
      DOI: 10.1007/s12080-017-0342-3
       
  • Joint evolution of interspecific mutualism and regulation of variation of
           interaction under directional selection in trait space
    • Authors: Atsushi Yamauchi
      Abstract: The present study theoretically examines the process by which interspecific mutualism is established with trait matching. The mathematical model includes joint evolution of the mutualistic relationship between two species and regulation of variation of interaction in one-dimensional trait space, assuming abiotic directional selection. The model considers three types of regulation: homeostasis against environmental variation, developmental stability, and acceptability of dissimilar mutualism partners (mutualism kernel). Mainly focusing on the developmental stability, the analysis indicates that the mutualism can evolve when (1) higher levels of developmental stability are more intensively degenerated by deleterious mutations, (2) the basal rate of deleterious mutation is low, (3) trait expression is less influenced by environmental factors, and (4) the specificity of mutualism is high. It also shows that the evolution of developmental stability can promote the evolution of mutualism with trait matching when the deleterious mutation bias disappears at a certain level of developmental instability. Evolution of homeostasis and mutualism kernel can be discussed in the similar way because of formal similarities in the model. In plant–pollinator interactions, it has recently been proposed that evolutionary increments of developmental stability in mutualistic traits might promote plant diversification. The present results partly support this hypothesis with respect to the evolutionary relationship between mutualism and developmental stability.
      PubDate: 2017-08-22
      DOI: 10.1007/s12080-017-0343-2
       
  • Handling overheads: optimal multi-method invasive species control
    • Authors: Christopher M. Baker; Paul R. Armsworth; Suzanne M. Lenhart
      Abstract: Invasive species are a pervasive problem worldwide and considerable resources are directed towards their control. While there are many aspects to invasive species management, deciding how to allocate resources effectively when removing them is critical. There are often multiple control methods available, each with different characteristics. For example aerial baiting has very high overhead costs, while animal trapping incurs a handling time (the trap must be reset after each capture). Here, we examine a particular challenge that managers commonly face when designing eradication programmes—specifically what type of control measure to rely on at different times during the eradication effort' We solve for optimal resource allocation strategies when there are two control methods available and one has overhead costs and the other has a handling time. We find that, if both controls are being used, the control with overhead costs should be used only at the beginning of a project, the other control should be used in the latter part of the project, and that there is generally an overlap where both controls are used. This contrasts with the strategies employed in many eradication projects, where ground control does not begin until aerial baiting has ceased.
      PubDate: 2017-08-15
      DOI: 10.1007/s12080-017-0344-1
       
  • Reduction of species coexistence through mixing in a spatial competition
           model
    • Authors: Senay Yitbarek; John H. Vandermeer
      Abstract: Many ecological systems exhibit self-organized spatial patterns due to local interactions. Such patterns can promote species diversity and therefore serve as an important mechanism for biodiversity maintenance. Previous work has shown that when species interactions occurred at local spatial scales, species diversity was greatest when robust mosaic spatial patterns formed. Also, intransitive interactions led to the emergence of spiral patterns, frequently resulting in multispecies coexistence. In some instances, intransitive interactions reduced species diversity as the consequence of competitive hierarchies. Here, we extend and broaden this line of investigation and examine the role of global competition along a continuum ranging from spatial mosaics to spiral patterns. While previous models have predicted that species diversity is reduced when interactions occur over larger spatial scales, our model considers the effects of various levels of mixing on species diversity, in the context of various network structures as measured by the covariance of row and column sums of the competition matrix. First, we compare local competition (unmixed system) versus global competition (mixed systems) and show that greater species diversity is maintained under a positive covariance. Second, we show that under various levels of mixing, species diversity declines more rapidly under a negative covariance. Lastly, we demonstrate that time to extinction in our model occurs much more rapidly under a negative covariance.
      PubDate: 2017-08-09
      DOI: 10.1007/s12080-017-0341-4
       
  • The impact of species-neutral stage structure on macroecological patterns
    • Authors: Rafael D’Andrea; James P. O’Dwyer
      Abstract: Despite its radical assumption of ecological equivalence between species, neutral biodiversity theory can often provide good fits to species abundance distributions observed in nature. Major criticisms of neutral theory have focused on interspecific differences, which are in conflict with ecological equivalence. However, neutrality in nature is also broken by differences between conspecific individuals at different life stages, which in many communities may vastly exceed interspecific differences between individuals at similar stages. These within-species asymmetries have not been fully explored in species-neutral models, and it is not known whether demographic stage structure affects macroecological patterns in neutral theory. Here, we present a two-stage neutral model where fecundity and mortality change as an individual transitions from one stage to the other. We explore several qualitatively different scenarios, and compare numerically obtained species abundance distributions to the predictions of unstructured neutral theory. We find that abundance distributions are generally robust to this kind of stage structure, but significant departures from unstructured predictions occur if adults have sufficiently low fecundity and mortality. In addition, we show that the cumulative number of births per species, which is distributed as a power law with a 3/2 exponent, is invariant even when the abundance distribution departs from unstructured model predictions. Our findings potentially explain power law-like abundance distributions in organisms with strong demographic structure, such as eusocial insects and humans, and partially rehabilitate species abundance distributions from past criticisms as to their inability to distinguish between biological mechanisms.
      PubDate: 2017-07-04
      DOI: 10.1007/s12080-017-0340-5
       
  • Modeling changes in predator functional response to prey across spatial
           scales
    • Authors: Diego F. Rincon; Luis A. Cañas; Casey W. Hoy
      Abstract: Extrapolation of predator functional responses from laboratory observations to the field is often necessary to predict predation rates and predator-prey dynamics at spatial and temporal scales that are difficult to observe directly. We use a spatially explicit individual-based model to explore mechanisms behind changes in functional responses when the scale of observation is increased. Model parameters were estimated from a predator-prey system consisting of the predator Delphastus catalinae (Coleoptera: Coccinellidae) and Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) on tomato plants. The model explicitly incorporates prey and predator distributions within single plants, the search behavior of predators within plants, and the functional response to prey at the smallest scale of interaction (within leaflets) observed in the laboratory. Validation revealed that the model is useful in scaling up from laboratory observations to predation in whole tomato plants of varying sizes. Comparing predicted predation at the leaflet scale, as observed in laboratory experiments, with predicted predation on whole plants revealed that the predator functional response switches from type II within leaflets to type III within whole plants. We found that the magnitude of predation rates and the type of functional response at the whole plant scale are modulated by (1) the degree of alignment between predator and prey distributions and (2) predator foraging behavior, particularly the effect of area-concentrated search within plants when prey population density is relatively low. The experimental and modeling techniques we present could be applied to other systems in which active predators prey upon sessile or slow-moving species.
      PubDate: 2017-06-17
      DOI: 10.1007/s12080-017-0338-z
       
  • Optimal sex allocation under pollen limitation
    • Authors: Philip H. Crowley; William Harris; Evelyn Korn
      Abstract: Most flowering plants are simultaneous hermaphrodites. Within species and even within local populations, sex allocation is usually highly plastic. Here, we link pollen sufficiency to the size of pollen-exchanging groups (i.e., pollen neighborhoods) and to pollen transfer efficiency, using an individual-based game-theoretic framework to determine the stable distribution of sex allocation that does not require the unrealistic assumption of infinitely large, panmictic populations. In the absence of selfing, we obtain the novel result that pollen limitation destabilizes hermaphroditism and favors separate sexes, whereas hermaphroditism remains stable without pollen limitation. With mixed mating, hermaphroditism is stable except when the fitness value of selfed offspring is less than half that of outcrossed offspring (i.e., strong inbreeding depression). In that case, the size of pollen neighborhoods, pollen transfer efficiencies, and the relative fitness of selfed offspring determine whether separate sexes or hermaphroditism is the stable outcome. The model thus predicts that separate sexes can derive from either of two ancestral states: obligate outcrossing under pollen limitation, or mixed mating (competing self-fertilization) under severe inbreeding depression. It also predicts conditions under which variance in sex-allocation among hermaphrodites within pollen exchanging groups along a gradient of pollen limitation can range from high (dioecy) to near zero (equal proportions of male and female investment).
      PubDate: 2017-06-16
      DOI: 10.1007/s12080-017-0339-y
       
  • The dynamical implications of human behaviour on a social-ecological
           harvesting model
    • Authors: Carling Bieg; Kevin S. McCann; John M. Fryxell
      Abstract: The dynamic aspects of human harvesting behaviour are often overlooked in resource management, such that models often neglect the complexities of dynamic human effort. Some researchers have recognized this, and a recent push has been made to understand how human behaviour and ecological systems interact through dynamic social-ecological systems. Here, we use a recent example of a social-ecological dynamical systems model to investigate the relationship between harvesting behaviour and the dynamics and stability of a harvested resource, and search for general rules in how relatively simple human behaviours can either stabilize or destabilize resource dynamics and yield. Our results suggest that weak to moderate behavioural and effort responses tend to stabilize dynamics by decreasing return times to equilibria or reducing the magnitude of cycles; however, relatively strong human impacts can readily lead to human-driven cycles, chaos, long transients and alternate states. Importantly, we further show that human-driven cycles are characteristically different from typical resource-driven cycles and, therefore, may be differentiated in real ecosystems. Given the potentially dramatic implications of harvesting on resource dynamics, it becomes critical to better understand how human behaviour determines harvesting effort through dynamic social-ecological systems.
      PubDate: 2017-03-21
      DOI: 10.1007/s12080-017-0334-3
       
 
 
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