Stability and Structure of Model Food-webs with Adaptive Behavior

• Main Author: Uchida, Satoshi
• Format: Others
• Language: English; en
• Published: 2008
• Online Access: http://tuprints.ulb.tu-darmstadt.de/965/1/uchidafinal.pdf; Uchida, Satoshi <http://tuprints.ulb.tu-darmstadt.de/view/person/Uchida=3ASatoshi=3A=3A.html> : Stability and Structure of Model Food-webs with Adaptive Behavior. [Online-Edition] Technische Universität, Darmstadt [Ph.D. Thesis], (2008)

In this dissertation, the influence of the adaptive behavior on stability and structure of model food webs is studied. First we study mainly analytically the influence of the implementation of population dynamics and of adaptive behavior on the number of links in a food web and on the stability of species with a small population size. By comparing models with Lotka-Volterra and Holling type II functional responses, models with and without predator avoidance, models with linear and nonlinear constraints on the foraging efforts, and diet selection models versus patch choice models, we find that adaptive foraging always has a stabilizing effect on small populations and that nonlinear functional responses and in particular nonlinear constraints on the foraging efforts lead to more realistic link numbers in the food web. We also investigate the influence of functional responses (Lotka-Volterra or Holling type), initial topological web structure (randomly connected or niche model), type of adaptive behavior (adaptive foraging and predator avoidance) and the type of constraints on the adaptive behavior (linear or nonlinear) on the stability and structure of large food webs. Two kinds of web stability are considered: one is the network robustness (i.e., the proportion of species surviving after population dynamics) and the other is the species deletion stability (i.e., persistence of a community after the deletion of a randomly chosen species). When evaluating the web structure, we consider link density as well as the trophic level structure. We show that the types of functional responses and initial web structure do not have a large effect on the stability of food webs, but foraging behavior has a large stabilizing effect. It leads to a positive complexity-stability relationship whenever higher complexity implies more potential prey per species. The other type of adaptive behavior, predator avoidance behavior, makes food webs only slightly more stable. The observed link density after population dynamics depends strongly on the presence or absence of adaptive foraging, and on the type of constraints used. We also show that the trophic level structure is preserved under population dynamics with adaptive foraging. Further the local and global stability of fixed points of Lotka-Volterra population dynamics with or without adaptive foraging are studied. We find a condition under which positive fixed points are stable. In terms of the local stability this condition applies to the potential link structure for the population dynamics without foraging dynamics, but to the effective link structure for the population dynamics with foraging dynamics, while in terms of the global stability the condition applies to the potential link structure for both cases. We also study the effect of intraspecific competition on the stability of fixed points and find that the intraspecific competition stabilizes the fixed point. Finally, we learn about the stability under evolution (i.e., persistence and resistance of webs under long-term changes of linkage patterns) with and without adaptive foraging. It is found that model food webs without adaptive foraging are unstable under evolutionary dynamics, i.e., they collapse after some time regardless of the details of the model, and the resulting food webs have only one trophic level. Thus a complex food web cannot be produced or sustained by the model. In contrast to this, it is shown that food webs with adaptive foraging persist in time under evolution and resulting food webs have more than one trophic levels.