MERI

MEADOWLANDS BIODIVERSITY: WHAT DO BUTTERFLIES, ODONATES, AND FROGS TELL US?

Abstract: In many areas of the world, frogs are affected by multiple environmental stresses, therefore the ability of frogs to tolerate urban conditions is of interest. In spring 2006, I surveyed calling frogs during three periods at each of two freshwater sites in the Hackensack Meadowlands just outside New York City in northeastern New Jersey, USA. I detected small choruses of a single species, southern leopard frog (Rana sphenocephala utricularia), at multiple wetland and pond locations within each site. The occurrence of populations of this species in the Meadowlands is noteworthy because it is rare or disappearing in nearby regions. The tolerance of southern leopard frog for slightly brackish water and the persistence of small areas of adjoining uplands may enable it to survive in a coastal urban environment.

Butterflies and odonates (dragonflies and damselflies) are of interest to researchers and naturalists because they integrate multiple features of the environment and are charismatic. I tested a strip transect sampling technique for adult odonates and butterflies in the Hackensack Meadowlands, New Jersey, an urban wetland complex. With a partner, I sampled five 1-km walking transects on dirt roads, divided in 100 m segments at 10 min each segment. We identified and counted all adult odonates and butterflies seen within 5 m either side of the roadbed, once each transect, on mornings at the end of June 2006. Counts totaled 106 individuals of 21 species of butterflies, and 303 individuals of 22 species of odonates (12 dragonflies, 10 damselflies). Damselflies were virtually limited to two transects. Four additional species of butterflies and two of odonates were recorded within 100 m of the transects on the survey days. We identified and ranked abundance of woody plants and selected nectar plants on transects by segment. Dragonfly abundance and species richness, and butterfly abundance and richness, were similar among transects. Damselfly abundance and richness, and the rank sums and species richness of trees, shrubs, vines (woody and herbaceous combined), and nectar plants were significantly different among transects. Dragonfly abundance and richness were negatively correlated with almost all woody plant rank sum and richness variables (all p < 0.03), damselfly abundance and richness were positively correlated with all woody plant rank sum and richness variables (all p < 0.02), but butterfly abundance and richness were not correlated with any vegetation component including nectar plants (all p > 0.2). Apparently dragonflies and butterflies are mobile enough to adjust their activities to spatial variation in vegetation. The butterfly and odonate faunas of the Meadowlands have moderate species diversity but lack many specialized species. Our transect method seems effective for sampling urban butterflies and odonates in the Meadowlands and should be tested in other urban and non-urban environments.