Consequences of Fragmentation of Tropical Moist Forest for Birds and Their Role in Predation of Herbivorous Insects

Abstract

The consequences of habitat alteration on the role of understory insectivorous birds as predators of herbivorous insects in tropical forests are poorly understood. To examine whether fragmentation may affect the top-down controls of herbivory, we compared the number of species, individuals, and the community structure of insectivorous birds between fragments and continuous tropical moist forest in Mexico. We also registered insect herbivore abundances and conducted a larvae predation experiment to evaluate the potential role of insectivorous birds as predators of herbivorous insects. We recorded 63 bird species from 22 families, 43 percent of which were insectivorous birds. Species richness, abundance, and diversity of the avian community were higher in continuous forest compared with forest fragments. For insectivorous birds in particular, there was low similarity in avian insectivore communities between forest types, and forest fragments had more heavily dominated communities of avian insectivores. During the dry season, forest fragments presented significantly higher predation rates on artificial caterpillars, and lower abundance of herbivorous Lepidoptera larvae, compared with continuous forest. Furthermore, there was a significant negative correlation between artificial caterpillar predation rate and larval Lepidoptera abundance, with higher rates of predation in sample sites of low Lepidoptera abundance. Hence, the potentially greater light in the dry season combined with a more dominated avian insectivore community in forest fragments may facilitate increased predation by avian insectivores, resulting in a decline in abundance of larval Lepidoptera, with implications for the process of insect-driven herbivory in forest fragments.

A review of the sentinel prey method as a way of quantifying invertebrate predation under field conditions

“…Artificial caterpillars were made of either plasticine ( n = 33), or dough (a mixture of flour, water, lard, and colorant, n = 11). Green ( n = 30) or brown ( n = 6) were common colour choices, but they could also have a green body with yellow (Loiselle & Farji‐Brener, ), or brown “head” (Faveri et al ., ; Ruiz‐Guerra et al ., ), or green body with eyespots (Hossie & Sherratt, ; ). Suzuki & Sakurai () used artificial caterpillars designed to mimic bird droppings (using larvae of Macrauzata maxima and Apochima juglansiaria as models).…”

Forest Fragmentation Drives the Loss of Insectivorous Birds and an Associated Increase in Herbivory

“…, Ruiz‐Guerra et al . ). As we did not apply bird observations at our focal trees we cannot prove that insectivorous birds were actually feeding on insect herbivores on E. natalense .…”

“…Therefore, forest fragmentation may hamper the trophic control of herbivorous insects by insectivorous birds, and thus interfere with tritrophic interactions between insectivorous birds, herbivorous insects, and plants (Ruiz‐Guerra et al . ). However, to our knowledge, so far only Karp et al .…”

Towards a standardized Rapid Ecosystem Function Assessment (REFA)

“…Mealworms (Tenebrio molitor) can be used as a commercially available replacement for aphids. Alternatively, exposing caterpillar dummies made from plasticine has been used in multiple studies both for invertebrate and vertebrate predators [55][56][57]. This method is well established [58] and has the additional advantage that predation marks left in plasticine dummies can be counted and attributed to different feeding types or even species [59].…”