Reproductive Biology of Three Sympatric Endangered Plants Endemic to Florida Scrub
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Biological Conservation 111 (2003) 235–246 www.elsevier.com/locate/biocon Reproductive biology of three sympatric endangered plants endemic to Florida scrub Margaret E.K. Evansa,*, Eric S. Mengesb, Doria R. Gordonc aDepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA bArchbold Biological Station, PO Box 2057, Lake Placid, FL 33870, USA cThe Nature Conservancy, Department of Botany, PO Box 118526, University of Florida, Gainesville, FL 32611, USA Received 25 August 2001; received in revised form 24 April 2002; accepted 20 September 2002 Abstract We investigated the reproductive biology of three plants endemic to rosemary scrub habitats on the Lake Wales Ridge of Florida, USA. We used hand-pollination experiments and observations of flowers and their insect visitors to determine their mating systems and pollination. Fruit or seed set after self pollination was 94, 97, and 8% of fruit or seed set after cross pollination in Eryngium cuneifolium (Apiaceae), Hypericum cumulicola (Hypericaceae), and Liatris ohlingerae (Asteraceae) respectively, indicating that the first two are self-compatible and the last is obligately outcrossing. All three depend on insects for seed production (4–7% fruit or seed set without insects). Diverse insects visit flowers of E. cuneifolium (101 species recorded), whereas L. ohlingerae is visited pre- dominantly by butterflies and H. cumulicola by one genus of bees (Dialictus, Halictidae). Our data indicate pollinator visitation does not currently limit seed production in E. cuneifolium or H. cumulicola, but does in L. ohlingerae. Despite the features they share (habit, habitat, disturbance regime), we found unique aspects of these species’ reproductive biology yielding unique risks to popu- lation viability. We suggest that multispecies recovery plans must consider several aspects of the biology of species with superficial similarities to be successful. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Eryngium cuneifolium; Florida scrub; Hypericum cumulicola; Liatris ohlingerae; Mating system 1. Introduction change hinge upon such variation (Fisher, 1958; Huen- neke, 1991). The loss of self-incompatibility alleles in Through its effects on demography and population self-incompatible species poses a special threat to genetics, reproductive biology has important con- genetic viability (Les et al., 1991; DeMauro, 1993; sequences for the viability of rare plant populations. Schemske et al., 1994). Genetic viability may also be Seed production of plants that rely on pollinators may affected negatively by inbreeding in the presence of be limited by pollinator abundance or behavior (polli- inbreeding depression (Charlesworth and Charlesworth, nator limitation; Bierzychudek, 1981). Pollinator limi- 1987; Lande, 1995; Lynch et al., 1995) or positively by tation or, at its extreme, pollinator failure could cause inbreeding to the extent that deleterious alleles can be seed production to fall below the level necessary for purged (Husband and Schemske, 1996; Byers and Wal- population viability (Lamont et al., 1993; Bond, 1994; ler, 1999). Steiner and Whitehead, 1996; Mawdsley et al., 1998; The Lake Wales Ridge (LWR) of central Florida, Spira, 2001). Mating patterns affect the amount of USA is an ancient dune system covering 150 Â 15 km, genetic variation found in plant populations (Hamrick with more than 20 species of federally-listed, narrowly- et al., 1991; Ellstrand and Elam, 1993; Hamrick and endemic higher plants (Christman and Judd, 1990; Godt, 1996). Genetic variation is important for genetic Dobson et al., 1997; USFWS, 1999). Declines of these viability, since evolutionary responses to environmental plants have been caused primarily by habitat loss and fire suppression. More than 15 years ago, Peroni and * Corresponding author. Abrahamson (1985) estimated that just 16% of the his- E-mail address: [email protected] (M. E. K. Evans). toric extent of scrub habitat on the LWR remained. In 0006-3207/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(02)00293-8 236 M.E.K. Evans et al. / Biological Conservation 111 (2003) 235–246 this study we examine the reproductive biology of three 1.1. The species of these species, Eryngium cuneifolium Small (Apiaceae), Hypericum cumulicola (Small) W. P. Adams (Hyper- Although all three species grow in rosemary scrub, icaceae), and Liatris ohlingerae B. L. Rob. (Asteraceae). they vary in a number of ecological traits (Table 1). All three are herbaceous perennials found in rosemary Only L. ohlingerae is commonly found in both rosemary scrub habitats and are federally listed as endangered scrub and a more mesic, oak-dominated community, species. Rosemary scrub occurs on elevated patches scrubby flatwoods. Scrubby flatwoods have few gaps (‘‘islands’’) of white sands throughout the Lake Wales between shrubs (Young and Menges, 1999), a shorter Ridge and other ridges in Florida (Menges and Hawkes, average fire return interval (5–20 years; Menges, 1999), 1998; Menges, 1999). Fire is an important ecological and are more abundant and spatially continuous on the force in rosemary scrub, which is dominated by the Lake Wales Ridge. The species also differ in postfire shrub, Florida rosemary (Ceratiola ericoides). Gaps recovery and how they respond to community-level among individuals of C. ericoides are large immediately changes with time-since-fire. Individuals of E. cuneifolium after fire and close with time-since-fire (Menges and and H. cumulicola are killed by fire, but populations Hawkes, 1998). At least 10 years are required before a recover from dormant seeds in the soil (Quintana- sufficiently continuous mass of fuel accumulates for fire Ascencio and Morales-Hernandez, 1997; Quintana- to return. Historical fire return intervals in rosemary Ascencio and Menges, 2000). In contrast, L. ohlingerae scrub probably ranged from 20 to 100 years, but fire has resprouts after fire from a belowground corm (Menges been suppressed over large parts of the LWR for the last and Kohfeldt, 1995), though resprouting is low after 60 years (Menges, 1999). some fires (Weekley, C. W., Menges, E. S., unpublished The species studied here have common and unique data). Recruitment of L. ohlingerae seedlings appears characteristics. If their similarities (habit, habitat, and episodic (Herndon, 1997). E. cuneifolium is most sensi- disturbance regime) lead to similar reproductive biol- tive to shrub encroachment into the open microsites in ogy, then detailed knowledge of the reproductive biol- which it does best (Menges and Kimmich, 1996; Menges ogy of each species would not be necessary. and Hawkes, 1998), H. cumulicola is somewhat less Alternatively, differences in their life span, reliance on sensitive to competition from shrubs (Quintana-Ascen- seeds to recover from fire, specialization to post-fire cio and Morales-Hernandez, 1997; Quintana-Ascencio gaps, and hence population dynamics could generate and Menges, 2000), and L. ohlingerae often grows different degrees of selection for reproductive assurance. among shrubs. From E. cuneifolium to H. cumulicola to Differences in reproductive biology resulting from these L. ohlingerae, these three species form a series from different selective pressures could then require species- shorter to longer-lived and greater to less demographic specific conservation approaches. To address the fluctuation (Menges et al., 2001; Menges, E. S., unpub- hypothesis that these species are reproductively uniform lished data). In addition, the first two species, which and evaluate risks to population viability arising from depend on seeds to recover from fire, appear to have reproductive biology, we investigated the floral biology, metapopulation dynamics (Quintana-Ascencio and flowering phenology, pollination, and mating systems of Menges, 1996; Quintana-Ascencio et al., 1998), which is E. cuneifolium, H. cumulicola, and L. ohlingerae. not evident in L. ohlingerae. Table 1 Ecological and life history traits of three endangered plant species endemic to the Lake Wales Ridge, Florida, USA Species Habit Range, Habitat Specialization Post-fire Median popualtion (and max no. extant to open space regenerationa size (and size lifespan)a populationsb fluctuation)a Eryngium Perennial 43 km Rosemary scrub Highc Seeds, limited 4280 (high) cuneifolium herb (10 year) 20 pop resprouting Hypericum Perennial 84 km Rosemary scrub Moderated Seeds 539 (high) cumulicola herb (10 year) 90 pop Liatris Perennial 109 km Rosemary scrub, none Resprouting 179 (low) ohlingerae herb (>10 year) 115 pop scrubby flatwoods Maximum lifespan was estimated from demographic monitoring of E. cuneifolium and H. cumulicola, and from observations of L. ohlingerae. The range of each species is expressed in km north–south along the long axis of the 160 Â 20 km Lake Wales Ridge, in Florida, USA. a From Menges et al. (2001) b From Dolan et al. (1999) c From (Menges and Hawkes, 1998, Quintana-Ascencio and Menges, 2000). d From (Quintana-Ascencio & Morales-Hernandez 1997, Quintana-Ascencio & Menges 2000). M.E.K. Evans et al. / Biological Conservation 111 (2003) 235–246 237 The three species also differ in genetic variation, as Our goal was to categorize each plant’s pollination in detected by isozymes. L. ohlingerae has the most varia- two respects: as generalist (many pollinating insect spe- tion (percent of loci polymorphic, number of alleles per cies) vs. specialist (few pollinating insect species), and in polymorphic loci, and observed heterozygosity; Dolan terms