Terrestrial invertebrates: An underestimated predator guild for small vertebrate groups

A fundamental goal of ecology is to describe how organisms co-exist in environments, including predator-prey interactions. However, one challenge for this field of study is that predation events can be rare and relatively difficult to observe, thus they are seldom quantified in nature. Vertebrates are the top predators in many systems, but large invertebrates such as spiders, mantids, and centipedes may also be important predators of small vertebrate groups. We used several approaches to determine the relative frequency of predation by invertebrate and vertebrate predators in terrestrial systems. We conducted 500 h of visual surveys and compiled observations of in situ predation events from 2014 to 2016 in north Queensland, Australia. Predation events were rarely observed: in 500 h of visual searches, we observed 9 instances of predation (vertebrates consuming another vertebrate, n = 4; invertebrates consuming a vertebrate, n = 5). In addition to spotlight surveys, we deployed 800 lizard-shape models to quantify attack frequencies on small lizards. While vertebrate predators were responsible for the most attacks on lizard models (76.7% and 93.3%, wet and dry season respectively), invertebrate predators were responsible for 23.3% and 6.8% of attacks. While predation events (of any kind) were rarely observed, we suggest that predation by invertebrate predators on vertebrate prey should not be overlooked in terrestrial systems. Invertebrate predators may play an important predatory role in shaping populations of small vertebrates, similar to more “typical” predators such as snakes, birds, and mammals.