Slow, slimy snails. How do they interact with their forest floor? The ecological function of slow moving/growing organisms is often overlooked because of our own inadequacy to interpret interactions outside of our day-to-day time scale. Watching a snail for 4 minutes becomes painfully monotonous as it moves less than a centimeter. However, by extending the observation from 4 to 40 minutes using a video time lapse function on most modern smartphones, these ‘boring’ organisms can be truly appreciated--driving species interactions at the soil surface.
This is a 40-minute time lapse video capturing a snail in one of our seed bait trays last summer. For five weeks, two Master's student in the Robert J Warren II ecological research lab at Buffalo State carried out seed tray trials to gain insight between ant dispersed seeds and the fitness of nearby ant nests. Seeds dispersed by ants are known as myrmecochorous. Myrmecochory has been previously described as a symbiosis, with the ants acquiring nutrients in exchange for transporting seeds away from their parent plant. These ant-dispersed seeds over time have evolved structures called elaiosomes, which are fat rich appendages that entice ants into carrying the seeds back to their nest. Ant nests are perfect for the seeds to germinate, because they fluctuate less in temperature and moisture level. Seeds without elaiosomes are selected less by the ants because they don't provide a fatty treat to the colony.
This video shows that snails eat elaiosomes, which ultimately make seeds less desirable for dispersal. Although this interaction has been described in the scientific literature, the rate of elaiosome consumption by these unassuming forest gastropods was only predicted. In this one observation, 12 elaiosomes were stripped off of Sanguinaria canadensis seeds in 42 minutes. Our video indicates that an average sized snail can eat around 17 elaiosomes/hr. Snail abundance is wide ranging and highly dependent on ecosystem type (20-500 individuals/m2) so their interaction with the forests floor differs with their abundance (Mason 1970; Bishop 1977; Cameron 1981 and Riggle 1976). This video supports that snails may play a substantial role in species distribution, especially for myrmecochorous plants that grow in areas of high snail richness. Natural selection should favor the timing of myrmecochorous seed production when their ant dispersers are abundant, while their seed predators are not.
We were wondering why many of our seeds had their elaiosomes removed. By leaving a smartphone recording while we carried out the day’s tasks, we captured something cool. Plant parasitism in the form of snail seed predation is a noteworthy interaction that should be considered in driving species distributions. This just goes to show the benefits of close observation, even if you’re in the field working on an ongoing project. There are interactions unseen beyond our own day-to-day timeframe that can ultimately help describe why some species of the forest floor succeed, while some don’t.