The advantage of the rare: field experiments on density-dependent seed dispersal by avian frugivores
Open Access
- Author:
- Vizzachero, Benjamin Scott
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 21, 2018
- Committee Members:
- Tomas A. Carlo, Thesis Advisor/Co-Advisor
David A. W. Miller, Committee Member
Margaret C. Brittingham, Committee Member - Keywords:
- frugivory
dispersal
birds
anti-apostatic
density-dependence
fruit choice
diversity maintenance
mutualisms
mutualistic
negative density-dependence
seed dispersal
experiment
artificial fruit
fruit
abundance
fruit color
fruit traits
field experiment - Abstract:
- Frugivorous birds provide dispersal for a large portion of plant species, yet little research has explored how plant-frugivore mutualisms influence plant community diversity. Recent work in tropical forests demonstrates that many fruiting plant species which are rare in a particular time and place occupy a disproportionately high fraction of the diet of avian frugivores. This rare-biased or “anti-apostatic” pattern of frugivory is a previously unexplored mechanism promoting the maintenance of diverse plant communities. The present work entails the first attempt to determine experimentally if anti-apostatic frugivory is a general pattern among common frugivorous birds in multiple environments. Between September 2016 and October 2017, I performed field experiments in Argentina, Puerto Rico, and Pennsylvania in which I presented arrays of artificial fruit in contrast to a background of abundant real fruit. I varied the color and density of artificial fruit arrays and measured the interest of visiting birds with camera traps. I found that wild birds exhibited anti-apostatic selection in most, but not all circumstances. In four of five experiments, avian visitors were more interested in artificial fruit which appeared novel than those which resembled a common fruit in that environment. Avian visitors also made more visits-per-fruit in low-density arrays (10 fruit), compared to high-density arrays (100 fruit). This is the first experimental evidence for anti-apostatic frugivory, demonstrating that frugivorous birds may equalize seed dispersal in plant communities where abundances are imbalanced.