Dynamics Of A Seed Dispersal Mutualism

Author : James R. Wright (Ph. D. in natural resources)
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (135 download)

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Download or read book Dynamics of a Seed Dispersal Mutualism Between Avian Seed-hoarders and Nut-bearing Trees written by James R. Wright (Ph. D. in natural resources) and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Seed dispersal mutualisms between plants and animals often determine the structure and diversity of ecosystems. In eastern hardwood forests of North America, the mutualism between scatter-hoarding animals and nut-bearing trees is crucial in shaping the distribution of dominant tree species and the complex wildlife communities they support. Avian seed-hoarders, in particular Blue Jays (Cyanocitta cristata), are especially important long-distance dispersers of oak (Quercus) acorns and other small nuts, through their caching of seeds in the autumn for winter consumption. Since oak-dominated forests are declining across much of the eastern U.S. – through mesophication, disease, and introduced pests – understanding their relationship with jays is critical to determining how best to manage for increased oak dispersal and recruitment. In addition, the reintroduction of American chestnut (Castanea dentata) to its former range is anticipated in the near future, and jays are likely to play a key role in their natural dispersal from founder plantings. In this dissertation, I examine dynamics of the mutualism between avian seed-hoarders and oaks/chestnuts to determine how it will shape these two processes of forest change – oak decline and chestnut reintroduction. I approach this topic in two ways. First, I examine each stage of the dispersal process from selection of seeds by birds through growth and survival of seedlings, for two common oaks (white oak [Q. alba] and black oak [Q. velutina]) and American chestnut. Second, I examine the link between mast abundance and Blue Jay abundance and survival, to determine how jay populations will be influenced by oak forest declines. When assessing the seed preferences of jays and other avian seed-hoarders in southeastern Ohio (Chapter 2), I found that jays consistently preferred black oak acorns over chestnuts, and chestnuts over white oak acorns. The strength of their preference for black oak acorns increased in late fall/early winter, when all seeds were less available, suggesting perhaps a greater need for lipid-rich resources in winter. Their preference for chestnuts over white oak acorns, however, suggests that chestnuts may become an important resource for jays and other seed-hoarders in years of black oak mast failure. Likewise, jays will likely serve as effective dispersers (Chapter 3) of chestnuts in those years, as 6.2% of cached chestnuts produced seedlings surviving through the first growing season, compared to 3.8% for black oak and 2.6% for white oak acorns. In addition, the propensity of jays to cache seeds in shrubby early-successional areas may also be a boon for early recruitment of the more competitive chestnut seedlings. On the other hand, jays provided directed dispersal for black and white oak acorns, as stem emergence of planted seeds was greater at cache sites than random sites for these species, but not chestnut. One of the most limiting factors for dispersal effectiveness of jays was pilferage by rodents, with >80% of all cached seeds being pilfered. Dispersal distances by jays (up to 460m from parent trees) at my mostly contiguous forest site were shorter than those reported by other studies in more fragmented habitats (up to 4km), but still suggest great potential for recruitment and colonization for oak and chestnut seedlings. Overwinter survival of jays (Chapter 4) at my Ohio field site was much greater for adults (88%) compared to young birds (47%), but otherwise was not influenced by annual mast abundance or other weather-related factors. In an analysis of long-term bird and mast abundance datasets (Breeding Bird Survey, Christmas Bird Count, and Regional Mast Survey) across 15 years and 8 states, I found that winter abundance of jays was positively associated with red oak subgenus mast abundance and negatively associated with the previous year’s white oak mast abundance, indicating both direct and indirect influences of acorn abundance on jays. Breeding abundance of jays, however, was not clearly associated with mast abundance, suggesting that jay populations are not necessarily limited by mast. Taken together, my results highlight the dynamic nature of the relationship between nut-bearing trees and their avian seed-dispersers, which underscores the importance of considering plant-animal mutualisms when planning forest management and restoration efforts.