Abstract
I studied factors affecting seed dispersal of nut-bearing deciduous trees, and examined how dispersal processes might be altered by forest fragmentation in the Midwestern U.S. The seeds of oaks (Quercus), hickories (Carya), and walnuts (Juglans) are dispersed by rodents and blue jays (Cyanocitta cristata). If forest fragmentation alters the rodent communities in habitat remnants, this could have consequences for seed dispersal and tree recruitment. My analysis of rodent-species occurrence rates throughout northern Indiana adds to evidence that eastern gray squirrels (Sciurus carolinensis) are sensitive to fragmentation. This species did not occur in small or isolated forest patches, and did not occur >15 km from large contiguous riparian forests. I conducted a 3-yr experiment to examine how seed survival would be affected in the absence of gray squirrels and fox squirrels (S. niger), 2 important seed dispersers. When Sciurus was excluded from seeds, seed survival was much lower than when these species could access seeds. However, seedling recruitment was not reduced in watersheds that lacked eastern gray squirrels. This is likely because fox squirrels, which were widespread and are tolerant of fragmentation, are able to disperse seeds in these areas. My experiments provided insight to the manner in which annual variation in seed production affects seed survival and dispersal distance. In years of low seed production, survival was extremely low for all seed types; in years of high seed production, survival was higher and varied with seed type. Rodents dispersed seeds to greater distances in seed-poor years than in seed-rich years, and dispersed more energy-rich food items to greater distances. These results provide support for escape and predator-satiation hypotheses, and challenge conventional optimal cache density models that suggest seeds should be dispersed shorter distances in low-seed years. My experiments also showed that seed removal rate data did not adequately index seed predation rates; this result has implications for conducting seed dispersal studies. Finally, I conducted feeding trials with blue jays to determine their dietary preferences for acorns of different oak species; this provided insight about jays' potential to act as long-distance dispersers of various oak species.
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Claims 9
Claim · model-written summary
Eastern gray squirrels were absent from small or isolated patches and sites over 15 km from large riparian forests.
- Taxon
- eastern gray squirrels
Sciurus carolinensise1 - Outcome
- did not occur in small or isolated forest patchese0
- Value
- >15 kme0
- Setting
- large contiguous riparian forestse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This species did not occur in small or isolated forest patches, and did not occur >15 km from large contiguous riparian forests.”
e1“eastern gray squirrels (Sciurus carolinensis) are sensitive to fragmentation.”
Claim · model-written summary
Excluding Sciurus lowered seed survival compared with access by squirrels.
- Treatment
- Sciurus was excluded from seedse0
- Outcome
- seed survivale0
- Direction
- lowere0
- Comparator
- these species could access seedse0
Quercus
Carya
Juglans
SciurusOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When Sciurus was excluded from seeds, seed survival was much lower than when these species could access seeds.”
e1“The seeds of oaks (Quercus), hickories (Carya), and walnuts (Juglans) are dispersed by rodents”
Claim · model-written summary
Seedling recruitment was not reduced where eastern gray squirrels were absent.
- Taxon
- nut-bearing deciduous treese1
- Interactor
- eastern gray squirrelsSciurus carolinensise0herbivore
- Outcome
- seedling recruitmente0
- Direction
- not reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“seedling recruitment was not reduced in watersheds that lacked eastern gray squirrels.”
e1“nut-bearing deciduous trees”
Claim · model-written summary
Fox squirrels may compensate through seed dispersal in watersheds without gray squirrels.
- Taxon
- nut-bearing deciduous treese1
- Interactor
- fox squirrels
.jpg?width=60)
Sciurus nigere0herbivore - Outcome
- disperse seedse0
- Qualifier
- likelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“This is likely because fox squirrels, which were widespread and are tolerant of fragmentation, are able to disperse seeds in these areas.”
e1“nut-bearing deciduous trees”
Claim · model-written summary
Seed survival was extremely low in low-production years.
Verbatim
e0“In years of low seed production, survival was extremely low for all seed types”
e1“nut-bearing deciduous trees”
Claim · model-written summary
Seed survival was higher and varied by seed type in high-production years.
Verbatim
e0“in years of high seed production, survival was higher and varied with seed type”
e1“nut-bearing deciduous trees”
Claim · model-written summary
Rodents dispersed seeds farther in seed-poor than seed-rich years.
Verbatim
e0“Rodents dispersed seeds to greater distances in seed-poor years than in seed-rich years”
e1“nut-bearing deciduous trees”
Claim · model-written summary
Rodents dispersed more energy-rich food items farther.
Verbatim
e0“dispersed more energy-rich food items to greater distances”
e1“Rodents dispersed seeds”
e2“nut-bearing deciduous trees”
Claim · model-written summary
Seed removal rate did not adequately index seed predation rate.
Verbatim
e0“seed removal rate data did not adequately index seed predation rates”
e1“nut-bearing deciduous trees”