Opuntia galapageia var. galapageia

Current name and scope of observations

POWO includes Opuntia megasperma and its nominotypical variety within O. galapageia var. galapageia. The older name remains a key to ecological studies on Española. The results below concern that population, described in the article as O. megasperma var. megasperma. [2-WWW] [Gibbs et al. 2008]

A tree-like cactus in a dry landscape

Adult plants on Española have a distinct trunk and a branched crown of flattened segments. The field study used features including armature and trunk bark to classify developmental stages. The crowns provide shade, while fallen fruits and segments become food and a water source for giant tortoises. [Gibbs et al. 2008]

The survey conducted in 2004 at Las Tunas covered 319 opuntias over 60 ha, comprising 125 adults, 34 subadults and 160 juveniles. Plant location, size, surrounding woody vegetation, fruiting and the occurrence of tortoise droppings were recorded. This allowed the recruitment pattern to be studied across the entire habitat area. [Gibbs et al. 2008]

Tortoises and the distribution of young opuntias

More droppings accumulated beneath larger adult opuntias, indicating use of these sites by tortoises. Young plants occurred more often farther from adults and in more open space. The authors consider the combined contribution of seed dispersal, trampling where animals concentrate, and plant competition. [Gibbs et al. 2008]

Comparisons with earlier observations indicated increasing numbers of young opuntias during the restoration of the tortoise population. At the same time, goats were being removed from the island and vegetation was changing. The field relationships therefore represent an ecological system undergoing reorganisation through several connected processes. [Gibbs et al. 2008]

Island diversity and DNA markers

The analysis of Galápagos opuntias published in 2009 compared morphological characters with four DNA regions. Substantial variation in appearance was accompanied by low variation in some of the sequences studied and weak separation of numerous lineages. The result defines the resolution of this marker set. Retaining local provenance and population characteristics remains important for research and conservation. [Helsen et al. 2009]