Experimental analysis of the territorial establishment of ayu, Plecoglossus altivelis

Territory holders and non-territory holders in Ayu fish coexist only in the population growth process due to hysteresis

Ayu fish form feeding territories during a non-breeding (growing) season. When the density of the fish increases, phases gradually change. In the early growing season, all fish can hold territories at low density. Once all territory sites are occupied, newcomers become floaters. As the density further increases, territory holders have to spend much more time in defending their own territory and lose the time to feed on algae. Eventually, all fish give up their own territories and then form a school. In contrast, when the density decreases, territories are directly reformed from the school. In short, ayu fish exhibit a different transition, called hysteresis, where the two transitions occur widely-apart from each other. The dynamics of this intrinsic phenomena has not been demonstrated in previous studies. We develop a rate equation to describe the population dynamics within territorial competition. Our model successfully reproduces territorial hysteresis and indicates that territory holders and floaters can coexist only in the process of population growth. Moreover, we also find that the two critical densities of territorial hysteresis are conspicuously different from each other when the increase of the density of floaters sharply influences (step-function-like) the territories.

Historical effect in the territoriality of ayu fish

Ayu fish form algae-feeding territories in a river during a non-breeding (growing) season. We build a cost-benefit theory to describe the breakdown and formation of territory. In the early stage of a growing season, all fish hold territories at low densities. Once all territory sites are occupied, excess fish become floaters. When fish density further increases, a phase transition occurs: all the territories suddenly break down and fish form a school. In contrast, when the fish density is decreased, territories are suddenly formed from the school. Both theory and experiments demonstrate that ayu should exhibit a historical effect: the breakdown and formation processes of territory are largely different. In particular, the theory in formation process predicts a specific fish behavior: an "attempted territory holder" that tries to have a small territory emerges just before the formation of territory.

What carnivore biologists can learn from bugs, birds, and beavers: a review of spatial theories

Information on the ecology and evolution of a species can be enhanced by studying spatial ecology. Even though space use has been a focus of carnivore research for decades, the theoretical framework for such studies remains poorly developed. Most spatial ecology theory has instead been developed and tested with invertebrates and expanded into fishery and ornithological research. The goal of this review is to examine spatial theories being tested in other taxonomic groups that could positively influence how carnivore biologists design studies. Details are provided from studies that illustrate methods to quantify space use, and four broad areas of spatial theory are reviewed: conspecific attraction, territory establishment, within-territory space use, and inheritance of space use. Suggestions are given on how carnivore biologists could incorporate each of these components into study designs. Carnivore biologists have opportunities to test spatial theory at small and large scales that could ultimately advance the entire field of spatial ecology. Although this review focuses on improving studies of terrestrial carnivores, our suggestions are relevant for studies of spatial theories across taxa.