Vucic-Pestic, Olivera (2010)
Functional Response of Terrestrial Predators.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

In chapter 2.1. we addressed the question if metabolic or foraging models predict more accurate the energy fluxes between population levels. We calculated from our experimental results, the field encounter rates and energy fluxes between predator and prey and compared the predictive power of both metabolic and foraging model. Our results show that despite clear power law scaling of metabolic and per capita consumption rates with body mass (according to the MTE), the per link predation rates for individual prey followed hump-shaped relationships with predator-prey body-mass ratios (according to OFT). Thus, in contrast to predictions of the metabolic models, our findings suggest that for any prey species per link and total energy fluxes are highest to its predators of intermediate body size than to its largest predators. In chapter 2.2. we extended the approach of chapter 2.1., to test if our previous results are of broad generality. We studied the functional responses in dependence on allometric scaling. These scaling relationships suggest that non-linear interaction strengths can be predicted by the knowledge of predator and prey body masses and integrating these relationships into population models will allow predicting energy fluxes, food web structures and the distribution of interaction-strengths across food web links based on the knowledge of the body masses of interacting species. In chapter 2.3. we addressed the question how increased temperatures affect ingestion and metabolic rates of terrestrial arthropod predators, and how warming affects the interaction strengths and consequently the stability of the system. We could show that warming does not only increase the metabolic requirements of the predators, but also that the temperature effects were weaker on ingestion than on metabolism. From the experimental short term per capita interaction strengths we calculated long term interaction strengths, and these predicted long term per capita interaction strength decreased with temperature. Our results indicate that on the one hand warming could increase intrinsic population stability while on the other hand decreasing ingestion efficiencies increase the extinction risk of the predators. To summarize, warming is expected to have complex and in some cases drastic effects on predator-prey interactions and food web stability. Our approach of chapter 2.3 presents a simplistic and mechanistic null model of warming effects on predator prey interactions in which thermal adaptation effects need to be included in future studies. In chapter 2.4. we extended the approach of chapter 2.3 to varying prey densities including the prey trait “movement pattern” into our experiments. Here we present strong evidence that warming imposes energetic restrictions on arthropod predators by decreasing their ingestion efficiency. Consequently, warming should increase stability of the populations. Our results also confirm the suggestion that warming increases the risk of predator starvation due to decreased ingestion efficiencies. The mechanistic functional response framework of chapter 2.4. may allow making detailed predictions about consequences of increasing temperature on predator-prey interaction strengths depending on metabolic and behavioural constrains. In chapter 2.5. we investigated the influence of changes in habitat structure on the functional response and in additional experiments the prey behaviour. We show that adding habitat structure alters the functional response type II to type IV (roller-coaster). Additional experiments on the prey behaviour suggest that the decreased consumption rates at high prey densities can be explained by aggregative defence behaviour. Analysing the net energy gain of the predators in both treatments showed that with habitat structure the predators’ energy net gain was limited at intermediate prey densities where prey aggregation reduced the consumption rate. Our results stress the importance of both, habitat structure and prey behaviour in shaping the functional response in soil-litter predator-prey interactions.

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