Lianas maintain insectivorous bird abundance and diversity in a neotropical forest

Abstract

The spatial habitat heterogeneity hypothesis posits that habitat complexity increases the abundance and diversity of species. In tropical forests, lianas add substantial habitat heterogeneity and complexity throughout the vertical forest profile, which may maintain animal abundance and diversity. The effects of lianas on tropical animal communities, however, remain poorly understood. We propose that lianas have a positive effect on animals by enhancing habitat complexity. Lianas may have a particularly strong influence on the forest bird community, providing nesting substrate, protection from predators, and nutrition (food). Understory insectivorous birds, which forage for insects that specialize on lianas, may particularly benefit. Alternatively, it is possible that lianas have a negative effect on forest birds by increasing predator abundances and providing arboreal predators with travel routes with easy access to bird nests. We tested the spatial habitat heterogeneity hypothesis on bird abundance and diversity by removing lianas, thus reducing forest complexity, using a large-scale experimental approach in a lowland tropical forest in the Republic of Panama. We found that removing lianas decreased total bird abundance by 78.4% and diversity by 77.4% after 8 months, and by 40.0% and 51.7%, respectively, after 20 months. Insectivorous bird abundance and diversity 8 months after liana removal were 91.8% and 89.5% lower, respectively, indicating that lianas positively influence insectivorous birds. The effects of liana removal persisted longer for insectivorous birds than other birds, with 77.3% lower abundance and 76.2% lower diversity after 20 months. Liana removal also altered bird community composition, creating two distinct communities in the control and removal plots, with disproportionate effects on insectivores. Our findings demonstrate that lianas have a strong positive influence on the bird community, particularly for insectivorous birds in the forest understory. Lianas may maintain bird abundance and diversity by increasing habitat complexity, habitat heterogeneity, and resource availability.

Sensitivity of Tropical Insectivorous Birds to the Anthropocene: A Review of Multiple Mechanisms and Conservation Implications

“…For example, Michel et al (2015a) argue that the most plausible explanation for the decline of insectivorous birds from some Central American forests is the local increase of collared peccaries (Pecari tajacu): This study focused on three unrelated insectivorous bird species in multiple Central American sites, and showed that (a) these species foraged preferentially in vine and liana tangles, (b) such viney substrates are more abundant where peccaries are least abundant (including experimental peccaryexclosure plots), and (c) abundant peccaries are associated with reduced abundance of these particular bird species. This lianasubstrate hypothesis is reinforced by the variety of insects that frequent vines and lianas (Schnitzer et al, 2020).…”

“…Lost insect substrates and microhabitats may be as important causes of bird declines as insect declines per se (Stratford and Stouffer, 2015;, although the two may be linked as in the case of tropical lianas (Schnitzer et al, 2020). Neotropical insectivorous birds are often substrate specialists, inferred from stereotyped feeding habits linked to morphology and behavior (Sherry, 1990, Supplementary Table 2), and the loss of which could jeopardize a variety of these birds' survival.…”

“…Many of these substrates are patchily available. For example, Checker-throated Antwrens (Epinecrophylla fulviventris), Dot-winged Antwrens (Microrhopias quixensis), and Ruddy-tailed Flycatchers (Terenotriccus erythrurus) depend on lianas and vines to concentrate the arthropod foods on which these birds feed (Michel et al, 2015a;Schnitzer et al, 2020), and potentially for safe nesting sites from snakes and other nest predators. In old-growth tropical forests lianas and vines are limited to disturbances like old treefall gaps, making this microhabitat temporally and spatially patchy.…”

The response of lianas to 20 yr of nutrient addition in a Panamanian forest

“…A wide variety of animals, including invertebrates, arboreal mammals, and many bird species use lianas as a food source, eating liana leaves, pollen, flowers, and fruits (Odell et al 2019). Many invertebrate herbivores specialize on liana species (Ødegaard 2000), and insectivorous bird species may feed on these specialized herbivores (Schnitzer et al 2020). Climbing animals such as monkeys, sloths, rodents, and ants depend on the structure and connectivity that lianas provide in the forest canopy (Chiarello et al 2004, Adams et al 2019).…”

Removing climbers more than doubles tree growth and biomass in degraded tropical forests

“…However, while preventing degraded forests from conversion could protect biodiversity, this study only considers the impact of climber removal on tree and AGB growth, ignoring the various functions of climbing plants in tropical forests. Their removal could have negative consequences for biodiversity, for example reducing the species richness of climbing plants, removing food and locomotion resources, and influencing the microclimate (Addo‐Fordjour et al, 2020 ; Arroyo‐Rodriguez et al, 2015 ; Campbell et al, 2015 ; Cosset & Edwards, 2017 ; Magnago et al, 2017 ; Putz et al, 2001 ; Schnitzer et al, 2020 ), though see Cerullo et al ( 2019 ). Our study finds that applying removal just to focal trees and not repeating treatment yield growth benefits while giving climbers greater chance to recover, but this will not be enough to prevent biodiversity losses from climber removal.…”