In nature, animals have to cope with constantly changing landscapes due to shifts in land use and the developing climate crisis. Changing landscapes can affect the resources available to animals and may alter how they move through their environment to find and eat food. While there is a wealth of information surrounding how a landscape affects an animal's movement, significantly less is known about how an animal's movement pattern varies over time within a changing landscape. To test how patterns of movement change through time in landscapes that vary in the amount of available food, researchers from Washington University of St Louis, USA, built their own tiny landscapes for the freshwater snail, Physa acuta, to cruise through.
First, Carl Cloyed and colleagues travelled to Illinois where they collected snails from the waters of the Mississippi River to bring back to the laboratory. In the wild, the snails graze on algae, so the researchers constructed tiny artificial ‘landscapes’ on panes of glass with varying amounts of algae (0%, 25%, 75% or 100% coverage). To ensure that the algae were distributed randomly across the glass, the researchers made a grid of 100 squares and removed algae from random patches. After depriving the snails of food for 1 day to ensure that they were hungry, the researchers placed the snails onto their temporary homes and set up video cameras with tracking software to measure their crawling speed and movement patterns.
The researchers initially examined whether the presence of food affected the snails’ speed. Because the snails should have been hungry and keen to satisfy their hunger at the beginning of the experiment, the researchers predicted that the molluscs would move slower in patches with food. Indeed, the movies confirmed their hunch, revealing that the snails moved faster when searching for food in barren patches and slower in algae-rich patches where they could gorge themselves. This supports the idea that internal states, like hunger, might drive animals to alter their speed depending on their environment.
Similarly, the researchers predicted that the snails’ movement patterns would differ depending on whether the molluscs were passing through regions of plenty or algae-free patches. Sure enough, the snails in bare patches moved in long straight lines to search better for food and the snails surrounded by abundant algae moved back and forth in short stretches to consume as much as possible. This suggests that the snails alter their movements depending on their local environment.
Cloyed and colleagues then wanted to test how the snails’ movement patterns changed as they roamed extensively over a 24 h period, comparing the molluscs’ movements during the first 12 h with their movements during the second half of the day. Initially, the snails moved in straight lines, but during the second half of the experiment, they took shorter, windier paths. This suggests that the presence of resources affects not only the snails’ movements at a single patch but also their movement patterns across their environment.
This is one of the first projects to experimentally demonstrate how an animal's landscape can affect its movement patterns over time. Movement characteristics – such as moving quickly in a straight line when hungry – could be included in models of animal movements to help us understand better the consequences of landscape changes on animal behaviour.
