10.5061/DRYAD.T1G1JWSZ8
Johnson, Marc
0000-0001-9719-0522
University of Toronto
Johnson, Mae
University of Toronto
Johnson, Oscar
University of Toronto
Johnson, Reagan
University of Toronto
The role of spines in anthropogenic seed dispersal on the Galápagos islands
Dryad
dataset
2019
dispersal ecology
Galapagos
Tribulus cistoides
2020-12-30T00:00:00Z
2020-01-23T00:00:00Z
en
https://doi.org/10.1002/ece3.6020
37446 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Dispersal has important ecological and evolutionary consequences for
populations, but understanding the role of specific traits in dispersal
can be difficult and requires careful experimentation. Moreover,
understanding how humans alter dispersal is an important question,
especially on oceanic islands where anthropogenic disturbance through
species introductions can dramatically alter native ecosystems. In this
study, we investigated the functional role of spines in seed dispersal of
the plant caltrop (Tribulus cistoides L., Zygophyllaceae) by anthropogenic
agents. We also tested whether anthropogenic or wildlife are more
important seed dispersers of T. cistoides on the Galápagos. Tribulus
cistoides is found on tropical mainland and oceanic island habitats. The
dispersal structure of T. cistoides is called a mericarp, and they are
typically protected by one pair of upper spines and a second pair of lower
spines, but the presence and size of spines varies within and between
populations. On the Galápagos, the upper and lower spines protect
mericarps from seed predation by Darwin’s finches. We tested whether
spines play a dual role in dispersal by factorially manipulating the
presence/absence of the upper and lower spines to simulate the natural
variation in mericarp morphology. The upper spines greatly facilitated
seed dispersal, whereas the lower spines had no discernible effect on
dispersal. The presence of upper spines increased dispersal rate on shoes
by pedestrians 23-fold, on fabrics (e.g. towels) and cars by nearly
2-fold, and the presence of upper spines increased dispersal distance by
cars 6-fold. When comparing dispersal rates in habitats with high (roads
and foot paths) versus low (arid forest) anthropogenic activity, dispersal
rates were demonstrably higher in the habitats with more human activity.
These results have important implications for understanding the ecology
and evolution of plant dispersal in the Anthropocene. Spines on the fruits
of T. cistoides play important functional roles in anthropogenic
dispersal, whereas native and introduced wildlife play a minor role in
dispersal on inhabited islands of the Galápagos. Our results imply that
seed predators and humans are jointly shaping the ecology and evolution of
contemporary populations of T. cistoides on the Galápagos.