Multiple Anthropogenic Pressures Lead to Seed Dispersal Collapse of the Southernmost Palm Jubaea chilensis

Abstract

Seed dispersal is a critical process for plant reproduction and regeneration. Successful recruitment depends on pre- and post-dispersal processes that complete a seed’s journey until becoming a new plant. However, anthropogenic stressors may disrupt the seed dispersal process at some stages, collapsing plant regeneration and hampering its long-term persistence. The Chilean palm tree Jubaea chilensis is the southernmost and the only non-tropical palm species, which currently relies on the scatter-hoarding rodent Octodon degus for seed dispersal. We assessed seed fate by measuring predation and dispersal rates through experimental fieldwork in the Palmar de Ocoa site (located within La Campana National Park) and the Palmar El Salto. We also used previous reports on seed harvest and seedling herbivory to depict the whole J. chilensis seed dispersal process and assess the relative importance of different anthropogenic pressures. We asked the following questions: (1) What is the effect of human harvesting on J. chilensis recruitment? (2) Do native and exotic rodents predate J. chilensis seeds in the same way? and (3) Does post-dispersal herbivory matter? We found that J. chilensis fruits are harvested for human consumption, reducing pre-dispersal available seeds by removing about 23 tons per season. Then, post-dispersal seeds at the Ocoa palm grove are heavily predated by exotic (Rattus rattus) and native (Octodon spp.) rodents; only 8.7% of the seeds are effectively dispersed by Octodon degus. At Palmar El Salto, 100% of the seeds were predated by Rattus rattus, precluding further analysis. Finally, 70% of the seedlings were consumed by exotic herbivores (mainly rabbits), resulting in a success rate of 1.81%. Only 7.9% of the surviving seedlings become infantile plants (4 year-old). Our assessment suggests that J. chilensis has aging populations with very few young individuals in disturbed sites to replace the old ones. For those reasons, we suggest increasing its conservation category to critically endangered as land-use change is rapidly fragmenting and shrinking the extant J. chilensis populations. We urge to take urgent actions to protect this relict palm, which otherwise may go extinct in the next decades.

Ecological Impacts of Exotic Species on Native Seed Dispersal Systems: A Systematic Review

“…Although exotic rodents can disperse seeds of exotic plant species, they can play a double role by behaving simultaneously as seed dispersers and predators of native plant species [ 62 ]. Lastly, exotic mammals can decrease native seed availability and the number of seedlings [ 68 ], and compete with native dispersers [ 69 ]. Thus, they can trigger a cascade of ecological effects, resulting in the decline in native plant species, the alteration of the structure and composition of the invaded habitat, and the loss of mutualistic interactions.…”

Temporal and behavioural niche partitioning underlies coexistence within a native‐exotic rodent assemblage exploiting a high‐value limited resource

“…However, J. chilensis fruits also represent a valuable resource for humans, as they remove large amounts of fruits from palm groves, dramatically limiting seed availability (Gallardo et al, 2006). Illegal human harvesting is an important anthropogenic stressor (Cordero et al, 2021), with humans removing over 90% of the overall fruit production in other J. chilensis palm groves (Cordero et al unpublished data). Since palm seeds are critical for rodents to overwinter and support the reproductive stage (Yates et al, 1994), resource limitation can be presumed to lead to competitive interactions among species (Dupre et al, 2017).…”

Niche models as a tool to inform restoration and conservation strategies: the case of Jubaea chilensis (palm, Arecaceae) and its seed disperser Octodon degus (rodent, Octodontidae)

“…However, rewilding must include overhunting regulations, since their lack explains why there are no natural populations of camelids in central Chile nowadays (see Westreicher et al, 2007). Alongside habitat rewilding, there is a need to control exotic rodents (Rattus rattus and Rattus norvegicus), as they are active seed consumers (Towns et al, 1997;Dukes and Mooney, 2004;Gosse et al, 2011;Cordero et al, 2021).…”