動植物關係的取食偏好與個體表現——以跨海拔分佈的專食性植食動物與寄主植物為例

Abstract

The relationship between herbivore feeding preference for host plants and herbivore performance is central to the study of plant–herbivore interactions. While the correlation and causation between herbivore preference and performance have been documented in latitudinal systems, little is known in altitudinal systems. To help fill up this knowledge gap, this altitudinal study tested four hypotheses: 1) Field herbivores, regardless of altitudinal origin, will show a feeding preference for higher-altitude plants. In other words, higher-altitude plants have a higher palatability. 2) Field plant traits will suggest a higher plant quality for herbivores at higher altitude, helping explain the altitudinal variation in plant palatability. 3) Accordingly, field herbivore performance (body size) increases with altitude, implying a link between field preference and performance. 4) A laboratory factorial experiment will support the causative link between preference and performance. Herbivores will perform better on plants collected from higher altitude (biotic factor), regardless of herbivore growth temperature (abiotic factor) or adaptation, if exists. Focusing on a specialist herbivore (Altica birmanensis) and its host plant (Polygonum chinense L.) at low vs. medium altitude (100 vs. 1000 m) in Taiwan, this study found a correlation between field herbivore preference and performance across altitude, consistently with latitudinal systems. In specific, field herbivores preferred higher-altitude plants. This higher preference (or plant palatability) was associated with the variation in field plant traits across altitude. Furthermore, the variation in field plant traits also correlated with field herbivore performance across altitude (larger body size at higher altitude). However, the correlation between field herbivore preference and performance across altitude was not supported by the laboratory experiment, in contrast to latitudinal systems. In specific, the laboratory results showed that an abiotic factor (temperature) was the most important factor affecting herbivore performance, compared to a biotic factor (plants with different palatability across altitude) or herbivores’ adaptation to abiotic or biotic factors. This suggests that while latitudinal and altitudinal systems share similar temperature gradients, the patterns of plant–herbivore interactions in each system could be driven by different factors.