Seed dispersal by wild pigs in Hawaiian forests
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2025-05
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The introduction of novel species around the world can lead to dramatic shifts in native ecosystems. In Hawaiʻi, invasive species have drastically altered the composition and function of native systems. It is important to understand the effects that these species have in order to anticipate and mitigate any detrimental impacts. Pigs (Suidae) are a prevalent invasive species in many parts of the world and occur on all continents except Antarctica. Within their native range, pigs perform a variety of ecosystem services, especially in forests where they increase soil nutrients through rooting and act as seed dispersers. Pig introduction outside of their native range, however, has proven to be detrimental to native species across the globe. In Hawaiʻi, wild pigs decrease native plant regeneration and abundance, prey on native ground-nesting birds, alter soil composition, and disperse non-native seeds. Studies done on other islands in Oceania have shown that pigs disperse native seeds in addition to non-native seeds. To determine if pigs are dispersing native seeds in Hawaiʻi, my thesis focused on the question: How do the species richness and total abundance of germinants in the scat compare to the fruiting species at low and high elevation sites over time? To examine this question, three high and three low elevation forests on the east side of the Island of Hawaiʻi were chosen based on elevation, precipitation, and dominant vegetation type. Elevation and precipitation were consistent amongst the two sets of sites, while native vs. non-native vegetation dominance was the determining selection factor. Scat was collected and germinated during four time points over the course of 19 months from December 2022 to July 2024 to understand seasonal variability. A total of 346 scat samples were collected and of those 173 germinated with a total of 33,508 seedlings. No native seedlings germinated from any of these samples during any time points. There was a greater species richness in the forest compared to the scat, with some germinants that were completely absent in the vegetation and available fruit. Total abundance of seedlings was greater at low elevation sites, but did not differ over time points. The two dominant species that germinated from the samples, P. cattleyanum and C. obtusifolia, were present in low elevation scat from all time points. Overall, this study highlights the fact that pigs are not dispersing native seeds and are facilitating colonization of non-native plants in areas where these plant species were not present.
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Wildlife management, seed dispersal, wild pigs
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60 pages
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