Reproduction and vegetative growth do not follow reciprocity theory in the C3 desert shrub ocotillo (Fouquieria splendens)

Abstract

Theory predicts the existence of a negative, reciprocal relationship between reproduction and vegetative growth. However, research and supporting data have focused on small, herbaceous plants growing in temperate environments. To test the underlying theory in a completely different environment, nine years of stem-specific data for a large, stem-succulent desert shrub explored the relationship between fruit production and growth. Measures of reproduction (annual presence/absence of infructescences and numbers of fruit capsules) and vegetative growth (annual increment of stem elongation) were measured in stems of two populations of ocotillo (Fouquieria splendens) growing in the Chihuahuan Desert in 2007–2015. Stem growth was significantly less in stems that produced infructescences than in stems lacking infructescences. The number of fruit capsules produced was also inversely related to stem growth. The reverse was not true. Stem growth prior to infructescence production did not have a significant impact on reproduction. The tenet that growth and reproduction are negative, reciprocal processes did not hold in ocotillo: reproduction negatively impacted vegetative growth, but growth did not impact reproduction. This atypical relationship in allocation to reproductive and vegetative tissues in this perennial desert shrub adds to the diversity of patterns known for optimal plant resource allocation.