Relative roles of resource stimulus and vegetation architecture on the paths of flies foraging for fruit

Abstract

Many animals use their perceptual abilities to orient and locate resources in architecturally complex environments. However, it is not well known how the strength of a stimulus source affects the geometry of animal movement in architecturally complex environments. We mapped the 3D vegetation architecture of four apple trees of varying morphology and age and recorded the paths of apple maggot flies Rhagoletis pomonella foraging for artificial fruit. We compared the observed movement with the one obtained from a random walk model on a graph to estimate both 1) the attraction radius and strength of a fruit and 2) the relative roles of the architecture of vegetation and of the strength of attraction of a fruit on the movement of flies. The attraction radius is the maximal distance at which a stimulus source biases the movement of individuals and the attraction strength measures how strong this bias is. Plant architectural complexity is defined according to both foliage density and its 3D distribution within the canopy. A single fruit induces a bias in the path orientation of an insect that is at a large distance, relative to a tree volume, but it has no effect on the step length of moves. The plant complexity makes a minor contribution to defining the radius of the sphere of attraction, but a large contribution to the attraction strength. Conditional on visiting the location, the plant architecture plays a minor role compared to that of the presence of the fruit. Our findings show that the complexity of the environment can alter the use of sensory information, which has important implications for animal movements in complex environments. The importance of our results in animal dispersal and foraging is considered.