Dytiscid beetle larvae (a.k.a. water tigers) have mouthparts that can pierce tadpole skin and suck out bodily fluids. These piercing mouthparts are almost as wide as the head and are kept neatly folded until the time of attack. A successful capture for a beetle larvae means death for the tadpole.
Water tigers make an amazing transformation between their larval and adult stages, but are on the hunt for tadpoles at both stages.
Megalopeterans have strong mandibles to catch and eat their prey. Look out tadpoles!
Libellulidae dragonfly larvae are a bit smaller, but are another predator in vernal pools.
The deeper I dug, the more cool things I found out about how predatory insects influence tadpoles. Wood frog tadpoles are well known to adapt their growth and behavior to cope with the predator pressures in a pool. Because many insect predators in vernal pools cue on prey movements, tadpoles move less in their presence to prevent attack. In pools with relatively high densities of insect predators tadpoles grow larger, thicker tail fins to better “sprint” away from a predator in case of attack. Tadpoles are so adapted to living with the dangers of insect predators that they can even “smell” them. Experiments have shown that even when predators cannot come in contact with tadpoles, the presence of a caged predator or even just water with predator chemical cues results in tadpoles that forage less and grow larger tails. Other experiments have demonstrated that exposure to predator cues can slow tadpole growth and result in smaller froglets emerging from pools.
Predatory insects are ubiquitous: we have found them even in our most urban sites. Because these insects are everywhere and their natural predation pressure on tadpoles can be strong disentangling the “true” response of tadpoles to urbanization (as opposed to predation) may not be so easy. Additionally, there are a multitude of urban factors – such as lawn fertilizers, road salts, reduced forest canopy cover, altered hydrology – which likely influence tadpole health, growth, and survival. This confluence of natural and anthropogenic factors makes my task more challenging, but armed with a broader ecosystem perspective that includes those underwater creepy-crawlies (and some multivariate statistics!) I hope to better understand tadpole responses to urbanization.
Brodie ED, Jr, and Formanowicz DR, Jr. (1983) Prey size preference of predators: differential vulnerability of larval anurans. Herpetologica 1983:67-75.
Newman RA (1992) Adaptive plasticity in amphibian metamorphosis. Bioscience 1992:671-678.
Relyea RA (2004) Fine-tuned phenotypes: tadpole plasticity under 16 combinations of predators and competitors. Ecology 85.1:172-179.
Relyea RA (2003) How prey respond to combined predators: a review and an empirical test. Ecology 84.7:1827-1839.
Skelly DK, Werner EE (1990) Behavioral and life-historical responses of larval American toads to an Odonate predator. Ecology 1990:2313-2322.
Skelly DK (1994) Activity level and the susceptibility of anuran larvae to predation. Animal Behavior. 47:465-468.
Van Buskirk J, Anderwald P, Lupold S, Reinhardt L, and Schule H (2003) The lure effect, tadpole tail shape, and the target of dragonfly strikes. Journal of Herpetology 37.2:420-424.