Resurgence of Harrisia portoricensis (Cactaceae) on Desecheo Island after the removal of invasive vertebrates: management implications

Abstract

Desecheo Island hosts a natural population of the higo chumbo cactus Harrisia portoricensis, listed as threatened under the US Endangered Species Act. The species was extirpated from mainland Puerto Rico and is restricted to the offshore islands of Mona, Monito and Desecheo. Herbivory by goats Capra hircus, rhesus macaques Macaca mulatta, and black rats Rattus rattus introduced to Desecheo Island have likely contributed to a population decline, with only a few individuals of higo chumbo reported in 2003. As part of a restoration program, goats have been eradicated, macaques are considered functionally extirpated, and actions to remove invasive rodents were completed in 2016 and confirmed as successful in 2017. Systematic monitoring was implemented between 2010 and 2013, including widespread searches for H. portoricensis, collecting data on population structure, number of individuals, height, number of branches and evidence of phenological events. After 4 yr of continuous monitoring, 72 individual plants were identified, which exhibited increased height and branching throughout the study years. No seedlings were observed and only a few juveniles recorded, suggesting a resurgence from suppressed adults with limited recruitment. Long-term monitoring is critical to understanding the population dynamics of this species on Desecheo Island. Efforts to safeguard this species on the island require completion of the invasive vertebrate removals and would benefit from a seed banking program and manual establishment of new populations.

Desecheo Island: a new home for Audubon's Shearwaters (<em>Puffinus lherminieri</em>)

“…However, we expect the establishment of an Audubon's Shearwater breeding colony to be slow given that breeding adults are typically site-faithful, leaving younger prospecting birds as the primary colonizers likely to respond to social attraction stimuli (Herrera-Giraldo et al 2021). While the results are promising and indicate that sound systems do attract Audubon's Shearwater, additional interventions are being considered to augment the likelihood of nesting, such as the establishment of artificial nests in areas of rocky shore vegetation (Correll and Correll 1982) and under dense vegetation (Mackin 2016). Desecheo Island presents natural cavities around the coastal perimeter that should be monitored during the breeding season since other populations of the Audubon's Shearwater in the Caribbean nest in caves and crevices (Bretagnolle and Precheur 2012).…”

The use of social attraction techniques to restore seabird colonies on Desecheo Island, Puerto Rico

“…Following cessation of bombing and subsequent designation as a NWR in 1976, managers eradicated damaging invasive and non‐native rats, goats and macaques from Desecheo to support biodiversity conservation goals and enable other restoration techniques, as seen elsewhere around the world (Jones et al., 2016). On Desecheo Island, several positive outcomes were documented following invasive mammal eradication, including an increase in the native cactus Harrisia portoricensis (Figuero, 2017) and arthropods such as butterflies, grasshoppers and crabs (Shiels et al., 2017). However, seabird response was limited, with no observed changes in the number of bridled tern or brown noddy breeding pairs across the island (Island Conservation, 2013; McKown, 2009; Wolf et al., 2010).…”

Recovery Planning for Natural Resources and Parks in Puerto Rico: Natural and Cultural Resources Sector Report, Volume I

“…Thus, prior to Hurricane Maria, it was on only the 3 small islands. This cactus is threatened by natural catastrophes, such as hurricanes; habitat modification; low genetic variation; and herbivory by invasive species, such as goats and rats, and the harrisia cactus mealybug (Aguirre et al, 2018;Environmental Conservation Online System, undated a;Figuerola-Hernández et al, 2017). Sebucán and higo chumbo were both likely affected by Hurricane Maria.…”

“…Higo chumbo is on the islands of Mona, Monito, and Desecheo. After 4 years of continuous monitoring (from 2010 through 2013), 72 individual plants were identified on Desecheo (Figuerola-Hernández et al, 2017). This cactus could also have been affected by storm damage and spread of the mealybug.…”