Perch selection in a guild of tropical dragonflies (Odonata: Libellulidae): relationships with body size and thermal ecology alt-text


Abstract

In the temperate zone, male perch height of co-occurring dragonfly species (Odonata: Libellulidae) often correlates with species body size. I tested for this relationship in a guild of tropical dragonflies at a wetland at La Selva Biological Station, Heredia, Costa Rica. Males of 12 species were observed perching in January–February 2016. Mean male perch height was positively correlated with species body size. For six common species, I quantified differences in perch substrate selection, relationships between diurnal activity, temperature and radiation, and aggressive interactions. The largest species, Libellula herculea and Orthemis discolor, exhibited typical heliotherm behavior: they used sunny perches at mid-day, and activity correlated more with radiation than temperature. Orthemis cultriformis, a slightly smaller heliotherm, was active at mid-day but used shadier perches. Micrathyria atra – previously classified as a “behavioral endotherm” – behaved accordingly, avoiding over-heating by flying early and perching in moderate light. The smallest common species, Erythrodiplax fervida, departed from the expected “thermoconformer” behavior by showing no relationship between activity and temperature, perching throughout the day in shaded grasses. The medium-sized Cannaphila insularis was unusual, perching 1 m higher than other species. Like larger heliotherms, activity occurred mid-day and correlated with solar radiation. Larger species exhibited greater degrees of interspecific aggression than smaller species. Cannaphila insularis is a docile species, but juveniles and females resemble the larger, more aggressive O. cultriformis. I hypothesize that C. insularis perches high to escape harassment and “reproductive interference” by O. cultriformis.

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