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Effects of warming and nutrient enrichment on feeding behavior, population stability and persistence of consumers and their resources
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Consumer-resource interactions are the basic building blocks of every food web. In spite of being a central research theme of longstanding interest in ecology, the mechanisms governing the stability and persistence of consumer-resource interactions are still not entirely understood. In particular, theoretical predictions on consumer-resource stability along gradients of temperature and nutrient enrichment diverge widely and are sometimes in conflict with empirical results. In this thesis I address these issues from the angle of the functional response, which describes a consumer’s feeding rate as a function of resource density. Specifically, I explore mechanistic, nutrient-based consumer-resource interaction models with respect to the influence of feeding behavior (the shape of the functional response), environmental temperature, nutrient enrichment, and resource quality on consumer-resource stability and persistence. In order to parameterize these models I performed extensive laboratory experiments with pairs of freshwater pelagic algae and grazers of the genus Daphnia, which are widespread, ecologically important model organisms.

I found a sigmoidal type III functional response in every studied Daphnia-algae species pair. The exact form of its shape is described by an exponent b which is determined by fitting functional response models to the experimental data. A high value of b can stabilize consumer-resource systems under the otherwise destabilizing influence of nutrient enrichment, as predicted by a novel stability criterion relating b to the consumer’s prey handling time, food conversion efficiency and mortality. Estimated parameter values and, consequently, stability predictions are sensitive to the method of parameter estimation, and I propose a new estimation procedure that minimizes parameter uncertainty. Because many consumers’ feeding rates depend on temperature, warming is expected to strongly affect food web stability. In functional response experiments over a broad temperature gradient, I found that the attack rate coefficient and the maximum ingestion rate of Daphnia are hump-shaped functions of temperature. Moreover, the functional response exponent increases with warming towards stronger type III responses. Plugging these findings into a nutrient-based consumer-resource model, I found that predator persistence is a U-shaped function of temperature in nutrient enrichment-temperature space. Enrichment easily turns the system unstable when the consumer has a type II response, whereas a type III response opens up a large region of stability at intermediate, for the consumer optimal, temperatures. These findings reconcile seemingly conflicting results of earlier studies of temperature effects on consumer-resource dynamics, which can be mapped as special cases onto the enrichment-temperature space. I finally demonstrate the utility of three key model ingredients - temperature dependence of rate parameters, a mechanistic description of the dynamics of algal resources, and a type III functional response in Daphnia - by successfully implementing them in the description and explanation of phytoplankton-Daphnia dynamics in a mesocosm experiment exploring effects of warming on the spring succession of the plankton.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2016. , p. 27
Keywords [en]
consumer-resource, Daphnia, functional response, nutrient enrichment, parameter estimation, persistence, plankton, predator-prey, stability, temperature, type II, type III, warming
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-124876ISBN: 978-91-7601-544-5 (print)OAI: oai:DiVA.org:umu-124876DiVA, id: diva2:956201
Public defence
2016-09-20, Lilla Hörsalen (KB3A9), KBC, Umeå University, Umeå, 09:30 (English)
Opponent
Supervisors
Available from: 2016-08-30 Created: 2016-08-29 Last updated: 2018-06-07Bibliographically approved
List of papers
1. When is a type III functional response stabilizing?: theory and practice of predicting plankton dynamics under enrichment
Open this publication in new window or tab >>When is a type III functional response stabilizing?: theory and practice of predicting plankton dynamics under enrichment
Show others...
2015 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 12, p. 3243-3256Article in journal (Refereed) Published
Abstract [en]

The curvature of generalized Holling type functional response curves is controlled by a shape parameter b yielding hyperbolic type II (b = 1) to increasingly sigmoid type III (b > 1) responses. Empirical estimates of b vary considerably across taxa. Larger consumer-resource body mass ratios have been suggested to generate more pronounced type III responses and therefore to promote dynamic stability. The dependence of consumer-resource stability on b has, however, not been systematically explored, and the accurate empirical determination of b is challenging. Specifically, the shape of the functional response of the pelagic grazer Daphnia feeding on phytoplankton, and its consequences for stability, remain controversial. We derive a novel analytical condition relating b to local stability of consumer-resource interactions and use it to predict stability of empirically parameterized models of Daphnia and phytoplankton under enrichment. Functional response parameters were experimentally derived for two species of Daphnia feeding separately on single cultures of two different phytoplankton species. All experimentally studied Daphnia-algae systems exhibited type III responses. Parameterized type III responses are predicted to stabilize the modeled Daphnia-phytoplankton dynamics in some species pairs but not in others. Remarkably, stability predictions differ depending on whether functional response parameters are derived from clearance vs. ingestion rates. Accurate parameter estimation may therefore require fitting to both rates. In addition, our estimates of b for filter-feeding Daphnia are much smaller than predicted for actively hunting predators at similar consumer-resource body mass ratios. This suggests that the relationship between functional response shape and body mass ratios may vary with predation mode.

Place, publisher, year, edition, pages
John Wiley & Sons, 2015
Keywords
body size, clearance rate, consumer-resource dynamics, Daphnia, filter feeder, functional response, gestion rate, parameter estimation, phytoplankton-zooplankton dynamics, stability
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-114583 (URN)10.1890/15-0055.1 (DOI)000367287900012 ()2-s2.0-84953207347 (Scopus ID)
External cooperation:
Available from: 2016-02-16 Created: 2016-01-25 Last updated: 2023-03-24Bibliographically approved
2. Temperature dependence of the type III functional response in Daphnia
Open this publication in new window or tab >>Temperature dependence of the type III functional response in Daphnia
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-124872 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2018-06-07
3. Effects of warming on predator-prey interactions: a resource-based approach and a theoretical synthesis
Open this publication in new window or tab >>Effects of warming on predator-prey interactions: a resource-based approach and a theoretical synthesis
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-124873 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2018-06-07
4. Stoichiometric mismatch causes a warming-induced regime shift in experimental plankton communities
Open this publication in new window or tab >>Stoichiometric mismatch causes a warming-induced regime shift in experimental plankton communities
2022 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, article id e3674Article in journal (Refereed) Published
Abstract [en]

In many ecosystems, consumers respond to warming differently than their resources, sometimes leading to temporal mismatches between seasonal maxima in consumer demand and resource availability. A potentially equally pervasive, but less acknowledged threat to the temporal coherence of consumer-resource interactions is mismatch in food quality. Many plant and algal communities respond to warming with shifts toward more carbon-rich species and growth forms, thereby diluting essential elements in their biomass and intensifying the stoichiometric mismatch with herbivore nutrient requirements. Here we report on a mesocosm experiment on the spring succession of an assembled plankton community in which we manipulated temperature (ambient vs. +3.6°C) and presence versus absence of two types of grazers (ciliates and Daphnia), and where warming caused a dramatic regime shift that coincided with extreme stoichiometric mismatch. At ambient temperatures, a typical spring succession developed, where a moderate bloom of nutritionally adequate phytoplankton was grazed down to a clear-water phase by a developing Daphnia population. While warming accelerated initial Daphnia population growth, it speeded up algal growth rates even more, triggering a massive phytoplankton bloom of poor food quality. Consistent with the predictions of a stoichiometric producer–grazer model, accelerated phytoplankton growth promoted the emergence of an alternative system attractor, where the extremely low phosphorus content of the abundant algal food eventually drove Daphnia to extinction. Where present, ciliates slowed down the phytoplankton bloom and the deterioration of its nutritional value, but this only delayed the regime shift. Eventually, phytoplankton also grew out of grazer control in the presence of ciliates, and the Daphnia population crashed. To our knowledge, the experiment is the first empirical demonstration of the “paradox of energy enrichment” (grazer starvation in an abundance of energy-rich but nutritionally imbalanced food) in a multispecies phytoplankton community. More generally, our results support the notion that warming can exacerbate the stoichiometric mismatch at the plant–herbivore interface and limit energy transfer to higher trophic levels.

Place, publisher, year, edition, pages
Ecological Society of America, 2022
Keywords
alternative states, C:P ratio, Daphnia, ecological stoichiometry, food quality, mesocosm experiment, paradox of energy enrichment, plant-herbivore, temperature, warming
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-124874 (URN)10.1002/ecy.3674 (DOI)000780007500001 ()2-s2.0-85127759512 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, 016.0083Swedish Research Council, 621-2010-5316
Note

Originally included in thesis in manuscript form.

Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2023-09-05Bibliographically approved

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Uszko, Wojciech

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