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Title: Rainfall, neighbors, and foraging: The dynamics of a population of red harvester ant colonies 1988–2019
Changing climatic conditions are shaping how density mediates resource competition. Colonies of the seed-eating red harvester ant, Pogonomyrmex barbatus, live for about 30 years in desert grassland. They compete with con- specific neighbors for foraging area in which to search for seeds. This study draws on a long-term census of a population of about 300 colonies from 1988 to 2019 at a site near Rodeo, New Mexico, USA. Rainfall was high in the first decade of the study, and then declined as a severe drought began in about 2001–2003. We examine the effects on colony survival and recruitment of the spatial configuration of the local neighborhood of conspecific neighbors, using Voronoi polygons as a measure of a colony’s foraging area, and consider how changing rainfall influences the effects of local neighborhoods. The results show that a colony’s chances of surviving to the next year depend on its age and on the foraging area available in its local neighborhood. Recruitment, measured as a founding colony’s chance of surviving to be 1 year old, depends on rainfall. In the earlier years of the study, when rainfall was high, colony numbers increased, and then began to decline after about 1997–1999, appar- ently due to crowding. As rainfall decreased, beginning in about 2001–2003, recruitment declined, and so did colony survival, leading to a trend toward earlier colony death which was most pronounced in 2016. As rainfall declined, apparently decreasing food availability, more foraging area was needed to sus- tain a colony: although the number of colonies declined, the impact of crowding by intraspecific neighbors increased. These processes maintain over- dispersion on the scale of about 8 m, with transient clustering at larger spatial scales. In addition, other factors besides crowding, such as the colony’s regula- tion of foraging activity to manage water loss, appear to contribute to a col- ony’s survival. The adaptive capacity for selection on the collective behavior that regulates foraging activity may determine how the population responds to ongoing climate change and drought.  more » « less
Award ID(s):
1940647
NSF-PAR ID:
10316491
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Ecological Monographs
ISSN:
0012-9615
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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