MARK ENDRIES

Education:

Thesis research:  Modeling spacing patterns of a tropical forest rodent using radiotelemetry and geographic information systems (GIS).

The social structure of organisms has important consequences for population regulation.  Rodents have been the focus of numerous studies on spacing patterns.  Most such studies have been conducted in temperate ecosystems, and there is little information on spacing patterns of tropical rodents.  From June through August 1999 (the rainy season) and in January 2000 (the dry season), I studied an island population of the Central American spiny rat, Proechimys semispinosus, using radiotelemetry.  Radiotelemetry has advantages over the more common method of live-trapping because it allows for a finer-scale investigation and can reveal not only home range size and overlap but also how P. semispinosus utilizes space within its home ragne, whether food resources are defended, and burrow use.  Home ranges were calculated by the fixed kernel method.  To model food resources, all trees > 10 cm in diameter at breast height (DBH) withing the study site were mapped, individually tagged, identified to species, and surveyed monthly to determine fruiting dynamics.  Using the tree data, species composition of home ranges were identified.  To model burrow use, diurnal telemetry was conducted because P. semispinosus is nocturnal and typically rests during the day.  Burrow habitat was quantified by measuring nine variables at each burrow site.

P. semispinosus had larger home ranges during the rainy season than during the dry season, and males had marginally larger mean home range sizes than females.  P. semispinosus showed greater home range overlap during the rainy season than during the dry season.  Tree species compositions of home ranges differed from areas outside of home ranges in 13 of 16 individuals.  No single tree species or group of tree species caused the majority of differences in any of the individuals.  I located 36 burrows and identified nine instances of co-occupancy, with six involving a male and female, two involving two females, and one involving two males and a female.  Burrow locations were close to water and had sparse herbaceous cover.  Broadly-overlapping home ranges, males having larger home ranges than females, and sexually-active males having larger home ranges than sexually inactive males suggest that P. semispinosus has a promiscuous mating system.  Additionally, male home ranges contained more female burrows than did female home ranges, suggesting that males attempt to maximize interactions with females.  However, high density of P. semispinosus was recorded over the entire study, and the mating system of this species may vary with density.

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Last updated 22 February 2002