Spatial Population Dynamics by Edward McCauley
FULL TEXT FREELY AVAILABLE AT www.escholarship.org/uc/item/4dm5n489 . . . We examine how spatial ... more FULL TEXT FREELY AVAILABLE AT www.escholarship.org/uc/item/4dm5n489 . . . We examine how spatial subdivision of predator–prey systems affects colonization processes in metapopulations. Dynamics of the herbivorous spider mite Tetranychus urticae (prey) and the predatory mite Phytoseiulus persimilis are highly unstable on isolated bean plants (Phaseolus lunatus) and ultimately result in extinction of prey and predators. Assembling a collection of 90 plants without any dispersal barriers (a super-island experiment) does not modify the persistence of the predator–prey system. Subdividing the system into a metapopulation with barriers for dispersal (a collection of eight islands with 10 plants per island) leads to persistence of the predator–prey dynamics for many generations. In this paper, we use the time series of colonization events and prey and predator densities from the super-island and metapopulation experiments to understand how colonization processes of prey and predatory mites are altered by spatial subdivision. Using survival analysis, we estimate how prey and predator colonization probability is affected by densities of the colonist pool at different distances from the target plant. Contrasting the results from the super-island and metapopulation experiments reveals that spatial subdivision affects the discovery rate of prey outbreaks by predatory mites and differentially affects colonization by prey and predators. Prey colonization is primarily determined by local densities of prey in spatially subdivided systems, whereas predator colonization retains primarily “global” influences. Our analysis of colonization processes suggests mechanisms accounting for stability in the metapopulation experiments and provides the quantitative basis for the development of colonization functions to explore these mechanisms in predator–prey models of acarine systems.
Population Cycles & Chaos by Edward McCauley
Most species live in species-rich food webs; yet, for a century, most mathematical models for pop... more Most species live in species-rich food webs; yet, for a century, most mathematical models for population dynamics have included only one or two species. We ask whether such models are relevant to the real world. Two-species population models of an interacting consumer and resource collapse to one-species dynamics when recruitment to the resource population is unrelated to resource abundance, thereby weakening the coupling between consumer and resource. We predict that, in nature, generalist consumers that feed on many species should similarly show one-species dynamics. We test this prediction using cyclic populations, in which it is easier to infer underlying mechanisms, and which are widespread in nature. Here we show that one-species cycles can be distinguished from consumer–resource cycles by their periods. We then analyse a large number of time series from cyclic populations in nature and show that almost all cycling, generalist consumers examined have periods that are consistent with one-species dynamics. Thus generalist consumers indeed behave as if they were one-species populations, and a one-species model is a valid representation for generalist population dynamics in many-species food webs.
Papers by Edward McCauley
Oikos, Sep 1, 1996
A predator-prey model is investigated in which the prey population is assumed to have age structu... more A predator-prey model is investigated in which the prey population is assumed to have age structure and is governed by the McKendrick-von Foerster partial differential equation and the predator population is described by the classical Volterra-Lotka ordinary differential equation. Quite general hypotheses are assumed for the mortality function, the fertility function, and the functional responses of predation. Existence and stability of three biologically meaningful equilibria, corresponding to extinction of both species, persistence of one species prey, and coexistence of two species, are studied. A particular example and some numerical results are given.
Canadian Journal of Fisheries and Aquatic Sciences, 1987
Replicate algal communities were isolated from Lake Memphremagog (Quebec–Vermont) in large–volume... more Replicate algal communities were isolated from Lake Memphremagog (Quebec–Vermont) in large–volume enclosures, and the abundance of herbivores was changed in them to produce a gradient of herbivore biomass among enclosures. The performance of the phytoplankton and their phosphorus uptake was observed in response to these different levels of crustacean Zooplankton biomass. In general, reducing Zooplankton biomass did not lead to phosphorus-deficient algal communities. Seven field experiments were done in 1979, 1980, and 1981 Only two of these experiments produced algal communities in which the cycling rate of orthophosphate per unit algal biomass was modified by reduction of crustacean Zooplankton biomass.
Canadian Journal of Fisheries and Aquatic Sciences, Dec 1, 1992
It has long been recognized that there is a positive relationship between total phytoplankton bio... more It has long been recognized that there is a positive relationship between total phytoplankton biomass and eutroph.cat.on. Recent independent studies demonstrated that algal biomass (chlorophyll) actually responds in a non linear, s.gmoidal fash.on w.th increasing phosphorus levels among lakes. Chlorophyll has been considered (bv some authors) as an inconsistent estimate of algal biomass. Using a wide range of published data we first dem onstrate that the s.gmoidal nature of the phosphorus-biomass relationship is quite robust, anc1 noUimply gen erated by a systematic variation in the relationship between algal chlorophyll to cell volume ratio and nutrient levels We show that the s.gmoid relationship with total phosphorus persists whether algal biomass is meaured by chlorophyll or b.ovolume We hypothesize that this nonlinearity actually reflects an underlymg systeS variation m one or more of the components of total phytoplankton biomass. In this paper, we examine two functional size groups and show that the large inedible fraction exhibits a strong, nonlinear response to increasing nutrient levels, while the small ed.be algae do not vary systematically with phosphorus. We hypothesize that this discontinuous shift in the ratio of edible to inedible phytoplankton should be accompanied by concomi an shifts in the structure of the herbivore community. On sait depuis longtemps qu'il existe un rapport positif entre la biomasse phytoplanctonique totale et I'eutroph.sat.on. Des etudes independantes r< §centes confirmed que la biomasse algale (chlorophylle) re"aeit en fait selon une courbe non lin^aire sigmoVdale a ('augmentation du taux de phosphore dans les lacs. Certains auteurs cons.derent la mesure de la chlorophylle comme etant une evaluation peu coherente de la biomasse aleale D apres un large eventail de donnas publiees, nous demontrons d'abord que la nature sigmoidale de la relation phosphore-b.omasse est tres marquee et n'est pas simplement le r&ultat d'une variation systematique dans le rapport entre la chlorophylle algale et le volume cellulaire ainsi que la teneur en elements nutritifs Nous demon trons que le rapport sigrnoTdal avec le phosphore total subsiste, que la biomasse algale ait ete mesuree d'apres la chlorophylle ou le volume des bio-elements. Notre hypothese est la suivante : cette relation non lineaire reflete en n §alite une variation systematique sous-jacente d'un ou de plusieurs elements de la biomasse phytonlancto nique totale. Dans le present rapport, nous etudions deux groupes de taille fonctionnels, et montrons aue la grande fraction non comestible presente une forte reaction non lineaire a I'augmentation des taux d'ei^ments nutr.t.fs, tand.s que la petite fraction d'algues comestibles ne varie pas de facon systematique par rapport au phosphore. Nous pensons que cette variation discontinue dans le rapport phytoplancton comestible-phytoplancton non comestible doit etre accompagnee par des variations concomittantes dans la structure de la communaute herbivore.
Bulletin of Mathematical Biology, 1995
The effect of varying habitat dimensionality on the dynamics of a model predator prey system is e... more The effect of varying habitat dimensionality on the dynamics of a model predator prey system is examined using an individual-based simulation. The general results are that in one dimension fluctuations in abundance of prey and predators occur over a large range of spatial scales (extinctions occur over many spatial scales). In two dimensions (and low mobilities of prey and predators) the dynamics become more predictably periodic at local scales and constant at larger scales due to statistical stabilization. In three dimensions, the model can become "phase-locked" with prey and predators displaying oscillations in abundance over large spatial scales.
Ecology, Apr 1, 2004
Ecological interactions are often difficult to observe or manipulate directly, making it a challe... more Ecological interactions are often difficult to observe or manipulate directly, making it a challenge to evaluate competing hypotheses in natural systems. Semiparametric models can provide a powerful inverse approach to infer population processes from observational data because they allow an ecologist to model aspects of a system that are known, but allow the data to ''speak for themselves'' with regard to aspects that are unknown. However, (st)age-structured semiparametric models are plagued with demographic instabilities that can cause different combinations of interactions, including competing hypotheses, to predict the observed pattern equally well. We developed and tested two new solutions to these demographic instabilities that expand the range of life histories for which (st)age-structured semiparametric inverse methods can be used. We begin by reviewing the range of inverse methods, from fully parametric models in which the governing functions are completely specified, to semiparametric models that replace these functions with nonparametric curves. We illustrate how the demographic instabilities emerge and indicate the requirements that any successful solution must satisfy. Existing solutions use constraints that may conflict with ecological processes and cause strong biases in the inferred rates. Our first solution uses a new statistical constraint that is less restrictive than previous methods. Our second solution is a hybrid approach that supplements the less restrictive statistical constraint with a few estimates of the interaction rates. This hybrid approach provides a way of distinguishing among dynamical mechanisms without imposing constraints on ecological relationships.
Ecology, Jun 1, 2010
Many species of phytoplankton typically co-occur within a single lake, as do many zooplankton spe... more Many species of phytoplankton typically co-occur within a single lake, as do many zooplankton species (the ''paradox of the plankton''). Long-term co-occurrence suggests stable coexistence. Coexistence requires that species be equally ''fit'' on average. Coexistence mechanisms can equalize species' long-term average fitnesses by reducing fitness differences to low levels at all times, and by causing species' relative fitness to fluctuate over time, thereby reducing differences in time-averaged fitness. We use recently developed time series analysis techniques drawn from population genetics to estimate the strength of net selection (timeaveraged selection over a year) and fluctuating selection (an index of the variation in selection throughout the year) in natural plankton communities. Analysis of 99 annual time series of zooplankton species dynamics and 49 algal time series reveals that within-year net selection generally is statistically significant but ecologically weak. Rates of net selection are ;10 times faster in laboratory competition experiments than in nature, indicating that natural coexistence mechanisms are strong. Most species experience significant fluctuating selection, indicating that fluctuation-dependent mechanisms may contribute to coexistence. Within-year net selection increases with enrichment, implying that among-year coexistence mechanisms such as trade-offs between competitive ability and resting egg production are especially important at high enrichment. Fluctuating selection also increases with enrichment but is independent of the temporal variance of key abiotic factors, suggesting that fluctuating selection does not emerge solely from variation in abiotic conditions, as hypothesized by Hutchinson. Nor does fluctuating selection vary among lake-years because more variable abiotic conditions comprise stronger perturbations to which species exhibit frequencydependent responses, since models of this mechanism fail to reproduce observed patterns of fluctuating selection. Instead, fluctuating selection may arise from internally generated fluctuations in relative fitness, as predicted by models of fluctuation-dependent coexistence mechanisms. Our results place novel constraints on hypotheses proposed to explain the paradox of the plankton.
Freshwater Biology, Apr 1, 1996
This study involves an examination of two-and three-trophic-level food chains at two temperatures... more This study involves an examination of two-and three-trophic-level food chains at two temperatures (18 and 25°C) in order to determine how the addition of a carnivore to a predator-prey system can alter the dynamics of populations and how this effect may be temperature mediated. The system consisted of phytoplankton, Daphnia pulex and the flatworm Mesostoma ehrenbergii. 2. Although the plant-herbivore system is inherently unstable at 25°C, the addition of the carnivore led to a further destabilization of the Daphnia-algal dynamics at the higher temperature. No destabilization effect of the carnivore was noted at 18°C. At the lower temperature, all populations persisted and the carnivore induced changes only in the age structure of the Daphnia populations rather than in overall biomass. 3. The differential effects of the carnivore at two temperatures can be attributed to shifts in the life history, physiological rates and the reproductive strategy employed by Mesostoma. 4. Previous theoretical work has predicted that the addition of a third trophic level to an unstable predator-prey system should stabilize dynamics. Our results indicate that the effect of a carnivore on plant-herbivore dynamics can be significantly affected by ambient temperature.
Proceedings of The Royal Society B: Biological Sciences, Jun 22, 2001
Recent work with the freshwater zooplankton Daphnia has suggested that the quality of its algal p... more Recent work with the freshwater zooplankton Daphnia has suggested that the quality of its algal prey can have a signi¢cant e¡ect on its demographic rates and life-history patterns. Predator^prey theory linking food quantity and food quality predicts that a single system should be able to display two distinct patterns of population dynamics. One pattern is predicted to have high herbivore and low algal biomass dynamics (high HBD), whereas the other is predicted to have low herbivore and high algal biomass dynamics (low HBD). Despite these predictions and the stoichiometric evidence that many phytoplankton communities may have poor access to food of quality, there have been few tests of whether a dynamic predator^prey system can display both of these distinct patterns. Here we report, to the authors' knowledge, the ¢rst evidence for two dynamical patterns, as predicted by theory, in a single predator^prey system. We show that the high HBD is a result of food quantity e¡ects and that the low HBD is a result of food quality e¡ects, which are maintained by phosphorus limitation in the predator. These results provide an important link between the known e¡ects of nutrient limitation in herbivores and the signi¢cance of prey quality in predator^prey population dynamics in natural zooplankton communities.
The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or i... more The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.
Proceedings of The Royal Society B: Biological Sciences, Oct 7, 2014
Parasites often induce life-history changes in their hosts. In many cases, these infection-induce... more Parasites often induce life-history changes in their hosts. In many cases, these infection-induced life-history changes are driven by changes in the pattern of energy allocation and utilization within the host. Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them. Determining the causes and consequences of infectioninduced life-history changes requires the ability to experimentally manipulate life history and a framework for connecting life history to host and parasite fitness. Here, we combine a novel starvation manipulation with energy budget models to provide new insights into castration and gigantism in the Daphnia magna-Pasteuria ramosa host-parasite system. Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration. These results are consistent with an energetic structure where the parasite uses growth energy as a resource. This finding gives us new understanding of the role of castration and gigantism in this system, and how life-history variation will affect infection outcome and epidemiological dynamics. The approach of combining targeted life-history manipulations with energy budget models can be adapted to understand life-history changes in other disease systems.
Limnology and Oceanography, 1985
Canadian Journal of Fisheries and Aquatic Sciences, 2001
A controversial precept of aquatic ecology asserts that low ratios of nitrogen to phosphorus (NT'... more A controversial precept of aquatic ecology asserts that low ratios of nitrogen to phosphorus (NT') lead to noxious and sometimes toxic blooms of Qntwbacteria. Cyatmbactetia dominance is a major risk te human and ecosystem health. The stoichiometric control of Cyanobacteria therefore has beeome centnat to tkshweter reseurce management. This controversial concept is based on observed Cyanobecteria domieance in lakes with low N:P end the results of lab and field experiments. Here we analyze data fmm 99 of the temperate zone's most studied lakes and show that this model is flawed. We show that the risk Of water quality degradation by Cyanobecteria blooms is more strongly correlated with variatioo in total P, total N, or standing algae biomass thee the ratio of N:?! Risks associated with Cyanobacteria are therefore less associated with N:P ratios than a simple increase in nutrient concentrations and algal biomass. Rkum& : Un prkepte controvenC de l'kotogie aquatique veut que des faibtes rapports azote:phosphore (N:P) entrainent la formation de fleurs d'eau B cyanobactkies, no&es et parfois toxiques. Une dominance des cyenobact& ties constitee. en effet, un risque important pour la sent& hutmine et celle des tcosysthnes. Le contr6le stoichiom& tique des cyanobact&ies est aiesi dwenu tme des pr&occupetions principeles de la gestion des resseurces d'eau douce. Ce concept controve& se base sw l'observatiott de la d ominance des cyaeolxact&s dens les lacs g faibte rapport N:P et sur les r&wltafs d'expktiences en labaatoire et en nature. Nous emlyscms ici dea dcmkes pmwnaet de 99 des lacs tempkk les mieti Ctudies et d&montmns que ie male est incorrect Le rbque d'ute ddgraaation des eaex per les Beus d'eau i cyeoobeetkies est en corrdlaticm plus fate avec ks variations de P total, du N total ou de la biomesse des atgues qe'avec le rapport N:P. Les tisqoes relids atu cyattobecties sent done moies associ& ax rapports N:P qu'& la simple augmentation des concentmtions d'&neets nut&ifs et de la biomesse des algues: [Traduit par la Rklection] Cyanobacteria dominance in anthmpogenically eutrophic takes is an increasing problem that impacts recreation, ecosystem integrity, and human and animal health. Blooms of Cyanobactctia deposit unsightly, bad-smelling, mucilaginous clumps of dead and sencsciog cells oo the shore and surf&e of lakes, impeding recreational uses. Blooms of some Cyattobacteria pmduce toxins during growth or decay that kill aquatic animals, and have semiochemical properties (aotibiotic or alklopathic). Cyanobacterial poisoning of livestock, pets, and humans has been widely documented (Sivottctt 1996). Cyanotoxitts, including hepatotoxins, tteum~xins, cyto
Theoretical Population Biology, May 1, 2007
River ecosystems are the prime example of environments where unidirectional flow influences the d... more River ecosystems are the prime example of environments where unidirectional flow influences the dispersal of individuals. Spatial patterns of community composition and species replacement emerge from complex interplays of hydrological, geochemical, biological, and ecological factors. Local processes affecting algal dynamics are well understood, but a mechanistic basis for large scale emerging patterns is lacking. To understand how these patterns could emerge in rivers, we analyze a reaction-advection-diffusion model for two competitors in heterogeneous environments. The model supports waves that invade upstream up to a well-defined ''upstream invasion limit''. We discuss how these waves are produced and present their key properties. We suggest that patterns of species replacement and coexistence along spatial axes reflect stalled waves, produced from diffusion, advection, and species interactions. Emergent spatial scales are plausible given parameter estimates for periphyton. Our results apply to other systems with unidirectional flow such as prevailing winds or climate-change scenarios.
Ecology Letters, Dec 18, 2013
The interaction between the immune system and pathogens is often characterised as a predatorprey ... more The interaction between the immune system and pathogens is often characterised as a predatorprey interaction. This characterisation ignores the fact that both require host resources to reproduce. Here, we propose novel theory that considers how these resource requirements can modify the interaction between the immune system and pathogens. We derive a series of models to describe the energetic interaction between the immune system and pathogens, from fully independent resources to direct competition for the same resource. We show that increasing within-host resource supply has qualitatively distinct effects under these different scenarios. In particular, we show the conditions for which pathogen load is expected to increase, decrease or even peak at intermediate resource supply. We survey the empirical literature and find evidence for all three patterns. These patterns are not explained by previous theory, suggesting that competition for host resources can have a strong influence on the outcome of disease.
Canadian Journal of Fisheries and Aquatic Sciences, Jul 1, 1989
Proceedings of The Royal Society B: Biological Sciences, Nov 22, 1991
Limnology and Oceanography, Jul 1, 1992
Published data on mean annual epilimnetic total N (TN) and P (TP) were analyzed to find how TN:TP... more Published data on mean annual epilimnetic total N (TN) and P (TP) were analyzed to find how TN:TP varies with lake trophic status. TN:TP is high in oligotrophic lakes and very low in eutrophic lakes, declining in a curvilinear fashion with increased TP. Comparison of this trend with published N: P in lake nutrient sources suggests that TN: TP reflects the source of nutrients: the ratio is high in oligotrophic lakes because they receive their N and P from natural, undisturbed watersheds which export much less P than N; mesotrophic and eutrophic lakes receive various mixtures of nutrient sources that have lower average N: P; and very eutrophic lakes have N: P that correspond very nearly to the N: P of sewage. Two inflection points were identified in the TN: TP relationship (~20 and-100 fig TP liter1) the first probably reflecting the large difference between TN: TP in nutrient export from undisturbed terrestrial ecosystems and that of meso-and eutrophic sources such as urban and pasture land runoff and sewage, and the second probably reflecting increased rates of denitrification in eutrophic lakes. Analysis of published manipulation experiments shows that N limitation is not only significantly more frequent in lakes of low ambient TN:TP (TN:TP mass ratio s 14) but is also significantly more frequent in lakes with TP > 30 Mg liter"1.
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Spatial Population Dynamics by Edward McCauley
Population Cycles & Chaos by Edward McCauley
Papers by Edward McCauley