Functional robustness of seed dispersal by a remnant frugivore population on a defaunated tropical island

Kastner, Martin; Pollock, Henry S.; Savidge, Julie A.; Fricke, Evan C.; Rogers, Haldre S.

doi:10.1111/btp.12926

Cited by 5 publications

(6 citation statements)

References 49 publications

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“…2021) and “fruit islands” in Guam (Kastner et al. 2021), wherein avian dispersers create aggregated patches of fruiting plants. Halos around ʻōhiʻa suggest that birds moved seeds from intact forest areas into the grazed zones, starting new foci of native woody understory.…”

Section: Discussionmentioning

confidence: 99%

“…At Hakalau, many remnant ʻ ōhiʻa in fragmented areas today are surrounded by "halos" of native woody understory even though those forests did not have these woody understory communities in 1985 when the refuge was established (L. Pratt, U.S. Geological Survey, oral communication, 2013). These "halos" are similar to "fruit orchards" in Sweden (Arnell et al 2021) and "fruit islands" in Guam (Kastner et al 2021), wherein avian dispersers create aggregated patches of fruiting plants. Halos around ʻōhiʻa suggest that birds moved seeds from intact forest areas into the grazed zones, starting new foci of native woody understory.…”

Section: Top-down Reinforcement Of Ecosystem Statementioning

confidence: 94%

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Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

2022

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Feedbacks within ecosystems can lead to internal reinforcement of the current state providing ecosystem resilience. Often, multiple biotic interactions across trophic levels play a role in such feedbacks, yet these are generally studied independently, obscuring the relative importance of interactions among different factors. We look at various potential feedbacks in intact and degraded mesic forests on Hawaiʻi Island where managers have planted native Acacia koa (koa) trees in an attempt to jumpstart succession in former cattle pastures. These restoration forests, however, have not undergone secondary succession, instead maintaining a koa overstory with an exotic pasture grass understory. We contrasted different trophic level processes that influence the capacity for natural understory regeneration: feedbacks between bird-mediated seed rain and fruiting understory ("top-down"), as well as links between understory composition and microhabitats for native seed germination ("bottom-up"). We quantified bird-mediated seed rain under canopy trees along transects spanning intact, fragmented, and restoration forests. Along these transects, we established plots around focal overstory trees to measure abundance of fruiting understory species, ground cover (e.g., exotic grass, bryophyte), and obtained estimates of bird density to evaluate the contribution of each of these factors to seedling abundance. We also used a factorial seed addition/grass removal experiment to directly compare the influence of seed rain and germination substrate. We found evidence of both top-down and bottom-up feedbacks that reinforced the current state of each forest type. In the intact and fragmented forests, the combination of comparatively high seed rain and ample germination substrate is likely critical for maintaining a diverse forest system. In contrast, exotic grasses exhibit priority effects in restoration forests, inhibiting seed germination and effectively negating any benefits that could be derived from bird-mediated seed rain. Such internal reinforcement suggests that active, rather than passive, restoration would be beneficial to increase forest diversity in restoration areas.

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Section: Discussionmentioning

confidence: 99%

Section: Top-down Reinforcement Of Ecosystem Statementioning

confidence: 94%

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

2022

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“…This finding aligns with the findings of Rogers et al (2021) and demonstrates that the Micronesian flora today is primarily the result of millions of years of co-evolution of plants and their bird dispersers. The importance of native bird dispersal (Rogers et al, 2021;Kastner et al, 2021), therefore, should be emphasized and incorporated into conservation plans of endemic and native plant species, especially in places like Guam, where invasive snake populations have decimated bird populations on the island (Savidge, 1984;Rogers et al, 2017;Egerer et al, 2018;Kastner et al, 2021;Rogers et al, 2021), and can result in coextinction of plant species that depend on their dispersers (Rogers et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

Origin and evolution of the Micronesian biota: Insights from molecular phylogenies and biogeography reveal long‐distance dispersal scenarios and founder‐event speciation

Demeulenaere

Ickert‐Bond

2022

J of Sytematics Evolution

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Micronesian islands taxa show high endemism rates, but very little is known about their biogeographical histories. The lack of systematic biogeography is mainly due to insufficient phylogenetic research in Micronesia. With the recent increase in published molecular biogeographic data, we were able to, for the first time, answer fundamental biogeography questions by reviewing and analyzing numerous geological, ecological, and evolutionary studies. This review, in addition to providing an overview of Micronesian geological history, confirmed the importance of long‐distance dispersal mechanisms and founder‐event speciation, and morphological and physiological adaptations of plant propagules to cross vast stretches of ocean by wind, ocean currents, bird, or bat dispersal. These adaptations to habitat and geological features, including reef types, determined colonization success as well as inland dispersal and speciation mechanisms. We further identified the source areas of the Micronesian biota and reconstructed historical dispersal scenarios: a dominant Austro‐Melanesian dispersal scenario, an Indo‐Malaysian connecting to the Austro‐Melanesian dispersal scenario, and a Neotropical American and an African dispersal scenario toward Micronesia. Most generic origins were estimated between the Eocene and the Miocene and dispersed to Micronesia between the Miocene and the Pleistocene.

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“…Sa ˚li have a very broad diet and are the only native frugivorous bird species remaining on the island (Pollock et al 2020). An important consequence of their constrained distribution is the limitation of ecosystem services related to seed dispersal and consequent forest regeneration (Rehm et al 2018, Kastner et al 2021, which are currently geographically restricted on Guam. Although the persistence of native wildlife in urban refugia may be beneficial from a species conservation perspective (Shaffer 2018), significant range expansion into historical forest habitats is necessary to fulfil a broader vision of rewilding on Guam (Thierry and Rogers 2020).…”

Section: Discussionmentioning

confidence: 99%

Recent recovery and expansion of Guam’s locally endangered Såli (Micronesian Starling) Aplonis opaca population in the presence of the invasive brown treesnake

Pollock

Kastner

Wiles

et al. 2021

Bird Conservation International

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Summary Assessing the impacts of invasive predators on the demography and distribution of native species is critical for understanding mechanisms of species persistence and informing the design of recovery programmes. On the oceanic island of Guam, the introduction of the predatory brown treesnake Boiga irregularis after World War II caused the near-total loss of the native forest avifauna. Localised snake control measures have been implemented since the early 1990s, yet it remains poorly understood how they have impacted Guam’s remaining native bird populations. To address this question, we combined intensive area searches of Andersen Air Force Base (AAFB) with island-wide transect surveys and opportunistic sightings to provide a comprehensive update on the distribution and abundance of Såli (Micronesian Starling, Aplonis opaca) – one of Guam’s last extant native bird species. Area searches of AAFB, where the largest remnant of the Såli population persists, revealed a 15-fold population increase since the last survey in the early 1990s, and transect surveys and opportunistic sightings indicate incipient recolonisation of other urbanised areas of northern and central Guam. We estimate the current island-wide population size at ~1,400 individuals. The population increase can likely be attributed to a combination of snake control measures and the Såli’s ability to exploit urban refugia for nesting and roosting. Although these trends demonstrate some population recovery, a skewed age ratio (>90% adults and subadults) at AAFB and a highly urbanised distribution and low abundance outside AAFB indicate that snake predation continues to strongly impact the population. More intensive snake suppression efforts, particularly in forested areas, may allow for the Såli population to attain its former distribution and abundance on Guam. More broadly, our findings reinforce the importance of urban areas as refugia for some threatened species.

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Functional robustness of seed dispersal by a remnant frugivore population on a defaunated tropical island

Abstract: This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Cited by 5 publications

References 49 publications

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

Origin and evolution of the Micronesian biota: Insights from molecular phylogenies and biogeography reveal long‐distance dispersal scenarios and founder‐event speciation

Recent recovery and expansion of Guam’s locally endangered Såli (Micronesian Starling) Aplonis opaca population in the presence of the invasive brown treesnake

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