22 research outputs found
Mutualistic networks: moving closer to a predictive theory
Plantâanimal mutualistic networks sustain terrestrial biodiversity and human food security. Global environmental changes threaten these networks, underscoring the urgency for developing a predictive theory on how networks respond to perturbations. Here, I synthesise theoretical advances towards predicting network structure, dynamics, interaction strengths and responses to perturbations. I find that mathematical models incorporating biological mechanisms of mutualistic interactions provide better predictions of network dynamics. Those mechanisms include trait matching, adaptive foraging, and the dynamic consumption and production of both resources and services provided by mutualisms. Models incorporating species traits better predict the potential structure of networks (fundamental niche), while theory based on the dynamics of species abundances, rewards, foraging preferences and reproductive services can predict the extremely dynamic realised structures of networks, and may successfully predict network responses to perturbations. From a theoreticianâs standpoint, model development must more realistically represent empirical data on interaction strengths, population dynamics and how these vary with perturbations from global change. From an empiricistâs standpoint, theory needs to make specific predictions that can be tested by observation or experiments. Developing models using shortâterm empirical data allows models to make longer term predictions of community dynamics. As more longer term data become available, rigorous tests of model predictions will improve.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151249/1/ele13279_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151249/2/ele13279.pd
Epigenetic and phenotypic changes result from a continuous pre and post natal dietary exposure to phytoestrogens in an experimental population of mice
Background: Developmental effects of exposure to endocrine disruptors can influence adult
characters in mammals, but could also have evolutionary consequences. The aim of this study was
to simulate an environmental exposure of an experimental population of mice to high amounts of
nutritional phytoestrogens and to evaluate parameters of relevance for evolutionary change in the
offspring. The effect of a continuous pre- and post-natal exposure to high levels of dietary
isoflavones was evaluated on sexual maturity, morphometric parameters and DNA methylation
status in mice. Adult mice male/female couples were fed ad libitum either with control diet
(standard laboratory chow) or ISF diet (control diet plus a soy isoflavone extract at 2% (w/w) that
contained the phytoestrogens genistein and daidzein). In the offspring we measured: i) the onset of
vaginal opening (sexual maturation) in females, ii) weight and size in all pups at 7, 14, 21 and 42 days
post-natal (dpn) and iii) DNA methylation patterns in skeletal α-actin (Acta1), estrogen receptor-
α and c-fos in adults (42 dpn).
Results: Vaginal opening was advanced in female pups in the ISF group, from 31.6 ± 0.75 dpn to
25.7 ± 0.48. No differences in size or weight at ages 7, 14 or 21 dpn were detected between
experimental groups. Nevertheless, at age 42 dpn reduced size and weight were observed in ISF
pups, in addition to suppression of normal gender differences in weight seen in the control group
(males heavier that females). Also, natural differences seen in DNA methylation at Acta1 promoter
in the offspring originated in the control group were suppressed in the ISF group. Acta1 is known
to be developmentally regulated and related to morphomotric features.
Conclusion: This study demonstrates in mammals that individuals from a population subjected to
a high consumption of isoflavones can show alterations in characters that may be of importance
from an evolutionary perspective, such as epigenetic and morphometric characters or sexual
maturation, a life history character.We greatly appreciate the linguistic revision of the manuscript by Renée
Hill and critical review of the manuscript by Dr. Anders Lindroth. We are
very thankful for funding by FONDECYT projects 1010647 to PS and
1030309 to LV, CONICYT fellowship for graduate studies and MECESUP
grant for overseas training to CG, and NH&MRC project grant funding to
SJC
Fishing-induced life-history changes degrade and destabilize harvested ecosystems
Fishing is widely known to magnify fluctuations in targeted populations. These fluctuations are correlated with population shifts towards young, small, and more quickly maturing individuals. However, the existence and nature of the mechanistic basis for these correlations and their potential ecosystem impacts remain highly uncertain. Here, we elucidate this basis and associated impacts by showing how fishing can increase fluctuations in fishes and their ecosystem, particularly when coupled with decreasing body sizes and advancing maturation characteristic of the life-history changes induced by fishing. More specifically, using an empirically parameterized network model of a well-studied lake ecosystem, we show how fishing may both increase fluctuations in fish abundances and also, when accompanied by decreasing body size of adults, further decrease fish abundance and increase temporal variability of fishes' food resources and their ecosystem. In contrast, advanced maturation has relatively little effect except to increase variability in juvenile populations. Our findings illustrate how different mechanisms underlying life-history changes that may arise as evolutionary responses to intensive, size-selective fishing can rapidly and continuously destabilize and degrade ecosystems even after fishing has ceased. This research helps better predict how life-history changes may reduce fishes' resilience to fishing and ecosystems' resistance to environmental variations.Peer reviewe
A Network Perspective for Community Assembly
Species interactions are responsible for many key mechanisms that govern the dynamics of ecological communities. Variation in the way interactions are organized among species results in different network structures, which translates into a community's ability to resist collapse and change. To better understand the factors involved in dictating ongoing dynamics in a community at a given time, we must unravel how interactions affect the assembly process. Here, we build a novel, integrative conceptual model for understanding how ecological communities assemble that combines ecological networks and island biogeography theory, as well as the principles of niche theory. Through our conceptual model, we show how the rate of species turnover and gene flow within communities will influence the structure of ecological networks. We conduct a preliminary test of our predictions using plant-herbivore networks from differently-aged sites in the Hawaiian archipelago. Our approach will allow future modeling and empirical studies to develop a better understanding of the role of the assembly process in shaping patterns of biodiversity
Ecogeographical rules and the macroecology of food webs
AimHow do factors such as space, time, climate and other ecological drivers influence food web structure and dynamics? Collections of wellâstudied food webs and replicate food webs from the same system that span biogeographical and ecological gradients now enable detailed, quantitative investigation of such questions and help integrate food web ecology and macroecology. Here, we integrate macroecology and food web ecology by focusing on how ecogeographical rules [the latitudinal diversity gradient (LDG), Bergmannâs rule, the island rule and Rapoportâs rule] are associated with the architecture of food webs.LocationGlobal.Time periodCurrent.Major taxa studiedAll taxa.MethodsWe discuss the implications of each ecogeographical rule for food webs, present predictions for how food web structure will vary with each rule, assess empirical support where available, and discuss how food webs may influence ecogeographical rules. Finally, we recommend systems and approaches for further advancing this research agenda.ResultsWe derived testable predictions for some ecogeographical rules (e.g. LDG, Rapoportâs rule), while for others (e.g., Bergmannâs and island rules) it is less clear how we would expect food webs to change over macroecological scales. Based on the LDG, we found weak support for both positive and negative relationships between food chain length and latitude and for increased generality and linkage density at higher latitudes. Based on Rapoportâs rule, we found support for the prediction that species turnover in food webs is inversely related to latitude.Main conclusionsThe macroecology of food webs goes beyond traditional approaches to biodiversity at macroecological scales by focusing on trophic interactions among species. The collection of food web data for different types of ecosystems across biogeographical gradients is key to advance this research agenda. Further, considering food web interactions as a selection pressure that drives or disrupts ecogeographical rules has the potential to address both mechanisms of and deviations from these macroecological relationships. For these reasons, further integration of macroecology and food webs will help ecologists better understand the assembly, maintenance and change of ecosystems across space and time.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151318/1/geb12925_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151318/2/geb12925.pd
Ecological theory of mutualism: Robust patterns of stability and thresholds in twoâspecies population models
Mutualisms are ubiquitous in nature, provide important ecosystem services, and involve many species of interest for conservation. Theoretical progress on the population dynamics of mutualistic interactions, however, comparatively lagged behind that of trophic and competitive interactions, leading to the impression that ecologists still lack a generalized framework to investigate the population dynamics of mutualisms. Yet, over the last 90Â years, abundant theoretical work has accumulated, ranging from abstract to detailed. Here, we review and synthesize historical models of twoâspecies mutualisms. We find that population dynamics of mutualisms are qualitatively robust across derivations, including levels of detail, types of benefit, and inspiring systems. Specifically, mutualisms tend to exhibit stable coexistence at high density and destabilizing thresholds at low density. These dynamics emerge when benefits of mutualism saturate, whether due to intrinsic or extrinsic density dependence in intraspecific processes, interspecific processes, or both. We distinguish between thresholds resulting from Allee effects, low partner density, and high partner density, and their mathematical and conceptual causes. Our synthesis suggests that there exists a robust population dynamic theory of mutualism that can make general predictions.Theoretical progress on the ecology of mutualistic interactions comparatively lagged behind that of trophic and competitive interactions, leading to the impression that ecologists still lack a generalized framework to investigate the population dynamics of mutualisms. Yet, over the last 90Â years, abundant work has accumulated, with qualitatively robust predictions across inspiring systems and levels of mechanistic detail. We review and synthesize this work, finding that mutualisms tend to exhibit stable coexistence at high density and destabilizing thresholds at low density.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171206/1/ece38453_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171206/2/ece38453.pd
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