The role of leaf traits and bird-mediated insect predation on patterns of herbivory in a semiarid environment in central Mexico

Abstract

Background: In arid environments plants face aridity and herbivory, therefore it has been proposed that both are convergent selective forces. However the drivers of insect herbivory in these ecosystems remain poorly understood. Question: Does insect herbivory vary in two plant associations subject to different levels of aridity? To what extent differences in herbivory are determined either by foliar traits, or predation by birds? Study species: Citharexylum tetramerum, Viguiera pinnatilobata, and Solanum tridynamum. Study site: We compared two-plant associations: the mezquital with a closed canopy and wettest conditions and the tetechera a dry place with an open canopy at the Zapotitlán Valley, México. Methods: We evaluated leaf traits (N, C, water content, leaf strength and trichomes), herbivore insects abundance and the effects on herbivory when some predators are excluded. Results: Herbivory was higher in the drier site (tetechera) than in the more humid one (mezquital) in one year but not in the second one. In both plant associations herbivory increased when predators of herbivores were excluded. Plants in mezquital had more water and nitrogen content than plants in tetechera. The later had higher carbon concentration and carbon:nitrogen ratio, leaf strength and density of trichomes. Abundance of herbivore insects and insect predation were higher in the most arid site. Conclusions: Our results show that insect herbivory increases in the most arid site and that predation by birds plays a role as a driver of herbivory, while resistance to aridity seems to be the main driver of leaf structural characteristics. Key words: herbivory, leaf traits, bird predation, Tehuacán-Cuicatlán, plant defence. El papel de las características foliares y la depredación por aves en los patrones de herbivoría en un ambiente semiárido del centro de México ResumenAntecedentes: En ecosistemas áridos las plantas se enfrentan a la sequía y a la herbivoría, por lo cual se ha postulado que éstas pueden actuar como presiones de selección convergentes sobre los atributos foliares. Sin embargo, los determinantes de la herbivoría han sido poco explorados. Pregunta: ¿Los niveles de herbivoría varían en sitios con condiciones de humedad contrastantes? ¿La herbivoría está determinada por las características nutritivas/defensivas de las plantas o por la depredación por aves? Especies de estudio: Citharexylum tetramerum, Viguiera pinnatilobata, and Solanum tridynamum. Sitio de estudio: Comparamos dos asociaciones vegetales: el mezquital con un dosel cerrado y húmedo y la tetechera un sitio seco con un dosel muy abierto, en el Valle de Zapotitlán, México. Métodos: Evaluamos características foliares (N, C, contenido de agua, dureza y tricomas), la abundancia de insectos herbívoros y las consecuencias de la exclusión de algunos depredadores sobre los niveles de herbivoría. Resultados: Los niveles de herbivoría fueron mayores en el sitio más árido (tetechera) comparado con el mezquital pero solo en un año. La herbivoría aumentó cuando los dep...

Bird predation does not explain spatial variation in insect herbivory in a forest–tundra ecotone

“…In particular, a cross-biome comparison of bird consumption of arthropod prey reported 25-fold differences between Arctic tundra and tropical forests (Nyffeler et al 2018), whereas the study based on artificial caterpillars revealed no latitudinal trend in attack rates by birds (Roslin et al 2017). More rigorous experimental studies that simultaneously measure predator impacts on artificial and natural prey (e.g., , Ruiz-Guerra et al 2017 are badly needed to validate earlier work and to justify the further use of dummies in ecological and environmental research.…”

“…The importance of birds in protecting forests from insect damage was proved scientifically about a century ago (reviewed by Bruns 1960;Inozemtsev 1978), and meta-analysis of controlled experiments has confirmed that birds generally reduce plant losses to insects (Mäntylä et al 2011). However, the intensity of bird predation on plant-feeding insects may differ between habitat types (Inozemtsev 1978;Garibaldi et al 2010;Ruiz-Guerra et al 2017), between sites (Connor et al 1999;Brewer and Gaston 2003), and between plant species within a site (Holmes and Robinson 1981;Giffard et al 2012;Singer et al 2012); as the result, the actual contribution of bird predation to the observed variation in insect herbivory at different scales remains unclear. Even more importantly, the data available so far do not allow for prediction of the sign of correlation between bird's predation and insect herbivory: not only does bird impact decrease abundance of plant-feeding insects (Mäntylä et al 2011), but low insect availability also decreases abundance of insectivorous birds (Martin 1987;Thiollay 1988).…”

Effects of Florivory on Floral Visitors and Reproductive Success of Sagittaria lancifolia (Alismataceae) in a Mexican Wetland

“…The amount of florivory damage (Florivory Index, ) present in the male and female flowers was calculated using the same equation from the herbivory index of Dirzo and Domínguez [ 57 ] as follows: where X i is the florivory category (damage score, 0 to 5), n i is the number of flowers in the category X i evaluated, and N is the total number of flowers. The FI was then expressed as a percentage of florivory following the methodology proposed by Ruiz-Guerra et al [ 58 ], which is based on a cubic linear model with intercept set to zero: …”

“…where X i is the florivory category (damage score, 0 to 5), n i is the number of flowers in the category X i evaluated, and N is the total number of flowers. The FI was then expressed as a percentage of florivory following the methodology proposed by Ruiz-Guerra et al [58], which is based on a cubic linear model with intercept set to zero:…”