Habitat requirements and occurrence of Crematogaster pilosa (Hymenoptera: Formicidae) ants within intertidal salt marshes
Keywords:
Spartina alterniflora, Sapelo Island, niche, connectivityAbstract
Spartina alterniflora Loisel. (Poales: Poaceae) salt marshes provide unique conditions for organisms to develop specialized morphological and behavioral traits. Crematogaster pilosa Emery (Hymenoptera: Formicidae) ants nest in S. alterniflora stems and display polydomy (i.e., multiple nests per colony), which has not been observed in terrestrial populations of this species. We identified new colonies of C. pilosa in S. alterniflora dominated salt marshes of Sapelo Island, Georgia (USA), and characterized the vegetation structure associated with ant presence. Crematogaster pilosa colonies were found most often 2 to 10 m from tidal creek channels in areas with expansive intermediate-height S. alterniflora. Marsh patches with abundant brown leaf vegetation above the high water level were most likely to have ants present (P = 0.03). These areas have extensive vegetation that remains dry during tidal advances, are protected from tidal surges, and most often occur along depositional banks of tidal creeks. Ant populations do not occur in the upland portion of the S. alterniflora marsh, presumably due to a lack of elevated habitat. Persistence of C. pilosa within S. alterniflora salt marshes is tied to the availability of connected habitat that avoids tidal submersion. The narrow band of intermediate-height S. alterniflora plants along tidal creeks provides both the needed horizontal structure and dry vegetation, allowing a terrestrial ant to colonize this seemingly atypical environment.
Resumen
Las marismas de Spartina alterniflora Loisel. (Poales: Poaceae) proveen condiciones únicas a los organismos para el desarrollo de rasgos morfológicos y de comportamiento especializado. La hormiga, Crematogaster pilosa Emery (Hymenoptera: Formicidae) anidan en los tallos de S. alterniflora y demuestran la polidomia (nidos múltiples por colonia), que no se ha observado en las poblaciones terrestres de esta especie. Identificamos nuevas colonias de C. pilosa en marismas dominadas por S. alterniflora en la Isla Sapelo, Georgia (EE.UU.), y caracteriza la estructura de la vegetación asociada a la presencia de hormigas. Se encontraron las colonias de Crematogaster pilosa con mayor frecuencia de 2 a 10 m de los canales de las quebradas de marea en zonas con amplia S. alterniflora de intermedio-alto altura. Las áreas de las marismas con una abundancia de vegetación de hojas de color café por encima del nivel de agua fueron más propensas a tener hormigas presentes (P = 0.03). Estas áreas tienen una amplia vegetación que permanece seca durante los avances de marea, están protegidos por marejadas, y más a menudo se producen a lo largo de los bancos de deposición de canales de la marisma. Las poblaciones de hormigas no se presentan en la parte de las tierras altas de la marismae de S. alterniflora, presumiblemente debido a la falta de hábitat de altura. La persistencia de C. pilosa dentro de las marismas de S. alterniflora está ligada a la disponibilidad de hábitat conectadas que evite la inmersión de las mareas. La banda estrecha de las plantas de S. alterniflora de altura intermedia a lo largo de canales de marea provee tanto la estructura horizontal necesaria como la vegetación seca, lo que le permite una hormiga terrestre el colonizar este ambiente aparentemente atípico.
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