The method of localized charge distributions is used to analyze the difference in hydrogen bond strength between HOH···OH2 and [HOH···OH]- in terms of the competition between the electronic kinetic energy and potential energy. The main source of the difference is the relatively larger decrease in the intermolecular energy for the latter complex, due to the net charge and a more polar accepting lone pair. The decrease is interpreted semiquantitatively by using bond and lone pair dipoles. The shortening of the OO distance and the lengthening of the donating O−H bond are both shown to occur as a result of the stronger attraction. Implications for other short strong hydrogen bonds are discussed.

Systems of patchy, ephemeral resources often support surprisingly diverse assemblages of consumer insects. Aggregation of consumer individuals over the landscape of patches has been suggested as one mechanism that can stabilize competition among consumer species. One mechanism for larval aggregation is the laying of eggs in clutches by females traveling among patches to distribute their total fecundity. We use simulation models to explore the consequences, for coexistence of competitors, of larval aggregation that arises from clutch laying. Contrary to some previous treatments, we find that clutch laying can be strongly stabilizing and under certain conditions can be sufficient to allow competitors to coexist stably. We extend these models by considering clutch size as a variable that responds to the abundance of resource patches. Such a relationship might be expected because females should lay their eggs in fewer but larger clutches when the cost of travel among patches is high (because patches are rare). When females adjust clutch size in response to resource abundance, coexistence can be easiest when resource patches are scarce and most difficult when resources are abundant.

Insect attack can have major consequences for plant population dynamics. We used individually based simulation models to ask how insect oviposition behaviour influences persistence and potential stability of an herbivoreplant system. We emphasised effects on system dynamics of herbivore travel costs and of two kinds of behaviour that might evolve to mitigate travel costs: insect clutch size behaviour (whether eggs are laid singly or in groups) and female aggregation behaviour (whether females prefer or avoid plants already bearing eggs). Travel costs that increase as plant populations drop lead to inverse density dependence of plant reproduction under herbivore attack. Female clutch size and aggregation behaviours also strongly affect system dynamics. When females lay eggs in large clutches or aggregate their clutches, herbivore damage varies strongly among plants, providing probabilistic refuges that permit plant reproduction and persistence. However, the population dynamics depend strongly on whether insect behaviour is fixed or responds adaptively to plant population size: when (and only when) females increase clutch size or aggregation as plants become rare, refuges from herbivory weaken at high plant density, creating inverse density dependence in plant reproduction. Both herbivore travel costs themselves, and also insect behaviour that might evolve in response to travel costs, can thus create plant density dependence-a basic requirement for regulation of plant populations by their insect herbivores.

For insects exploiting spatially structured arrays of resource patches (host plants, fungi, carrion, etc.), the distribution of individuals among patches can have important consequences for the coexistence of competitors. In general, intraspecific aggregation of consumer individuals over the landscape of patches stabilizes competition. Oviposition behavior of individual females can generate aggregation of larvae across patches and, therefore, strongly influences the outcome of competition between co-occurring species. We used simulation models to evaluate the consequences (for the coexistence of competitors) of different movement behaviors by females before and between oviposition events. Coexistence times increase when females are more likely to travel among neighboring patches than among distant ones. Coexistence times are also longer when females begin egg laying near the site of their emergence. Preoviposition dispersal is, therefore, destabilizing. We also considered responses by females to edges of resource arrays. Edge effects are generally stabilizing, delaying competitive exclusion by increasing larval aggregation, but different responses to edges have dramatically different effects on coexistence. The longest coexistence times occur when edges are "sticky", such that females encountering an edge tend to remain there.