Abstract Detail

Conservation Biology

Powell, Emily [1], Krosnick, Shawn [2].

Advancements in the conservation of the federally endangered Short’s bladderpod (Physaria globosa: Brassicaceae).

Physaria globosa (Desv.) O’Kane & Al-Shehbaz (Short’s bladderpod) is a Federally endangered species listed as globally imperiled (G2) and limited to just 33 populations across Tennessee, Kentucky, and Indiana. Habitat degradation and loss appear to be the most significant barriers to long-term survival in P. globosa, compounded by limited population sizes and geographical isolation. However, one of the biggest limitations to our understanding of P. globosa is the paucity of fundamental data available on reproductive biology and life history in this species. Conflicting historical observations and uncertainty across states suggest that P. globosa varies in life strategy and may even exhibit “boom” and “bust” years. Factors such as resource availability, fragmentation, and plant competition may play a role in simultaneously decreasing both floral density and reproductive success by disrupting mutualistic pollinator interactions. Pollen limitation has been shown to be a limiting factor for seed production in fragmented populations, affecting smaller populations at higher rates than larger ones. Evaluating reproductive success across P. globosa range is essential given that plant population distributions have infinitely variable gradations of clumping, regular spacing, and density that impact genetic variation from outcrossing and pollen flow potential. Compatibility in P. globosa has yet to be documented in natural populations, although the genus Physaria is known to contain both self-compatible and self-incompatible species.

In 2021, two sites in Tennessee, two in Kentucky, and one in Indiana were chosen to determine which factors limit reproductive success across the range and how this potentially influences life history strategies. At each population, 10 focal plants were chosen at random and centered in 1 m2 plots to assess relationships between plant density, size of floral display (measured by number of flowering stems per plant), stem diameter, frequency of pollinator visitation, pollen limitation, and fecundity. Tennessee populations exhibited the highest average percent cover of P. globosa in plots, the most flowering stems per plant, and the largest basal stem diameters; Indiana had the highest percent cover of heterospecific species; and Kentucky had the lowest percent cover of heterospecific species. After counting successfully fertilized ovules in control and supplemental pollen treatments under fluorescence, both Kentucky populations (n = 169, p < 0.001) (n = 121, p = 0.03) and Indiana (n = 170, p < 0.001) appear to be pollen limited, while both Tennessee populations (n = 145, p = 0.48) (n = 162, p = 0.22) do not. Based on Spearman’s Rank Correlation using data from all five populations, the percent cover of both conspecific (r = 0.642, p = 0.0009) and heterospecific (r = 0.578, p = 0.0385) flowering plants do not appear to negatively affect P. globosa with respect to flowering stems and stem diameter. Further, the number of flowering stems per individual plant is strongly related to the basal stem diameter (r = 0.890, p < 0.001). Assessing genetic diversity within populations, as well as identifying predictive correlates between plant age and morphology, will contribute to a great understanding and facilitate the long-term survival of P. globosa.

1 - Tennessee Tech University, Biology, 1100 North Dixie Avenue, PENN 207, Cookeville, TN, 38501, United States
2 - Tennessee Tech University, Dept. Of Biology, 1100 East Dixie Avenue, Pennebaker Hall #207, Cookeville, TN, 38505, United States

endangered species
pollen limitation
life history.

Presentation Type: Oral Paper
Number: CB2002
Abstract ID:533
Candidate for Awards:None

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