Microhabitat and time-since-fire: effects on demography oF Eryngium cuneifolium (Apiaceae), a Florida scrub endemic plant

Eryngium cuneifolium Small. (Apiaceae) is a narrowly distributed endemic found only in Ceratiola ericoides (Florida rosemary)-dominated Florida scrub, a periodically burned, shrub-dominated habitat. Multivariate analyses using 22 ∗∗∗microhabitat characteristics indicated significant microhabitat and time-since-fire effects on survival, growth, and fecundity of 1287 individuals over a 4-yr period. Survival increased with distance to the nearest shrub, and plants in larger open patches had greater survival rates. Neighboring shrubs of Ceratiola ericoides and Calamintha ashei were associated with a higher mortality of E. cuneifolium than other neighboring shrub species. Survival was reduced by two-thirds over 4 yr (14% vs. 42%) for E. cuneifolium near C. ericoides. Sand accretion increased growth and fecundity. With greater time since fire, woody shrubs increasingly dominate and open patches shrink, significantly reducing survival, growth, and fecundity of E. cuneifolium. Effects were particularly dramatic between 2 and 7 yr postfire, when annual mortality increased from <10% to >30% (r = 0.74). This herbaceous species is dependent on an open habitat maintained by periodic fire. Belowground competition or allelopathy from shrubs probably restricts E. cuneifolium to recently burned, open patches within the most xeric parts of Florida scrub.     

Conservation implications of genetic variation in three rare species endemic to Florida rosemary scrub

Habitat conversion and fire suppression during the last 50 yr have greatly reduced and altered Florida scrub vegetation, resulting in threats to the persistence of its unique flora. As part of a larger conservation project, we investigated patterns of isozyme variation in three rare perennial scrub plants with overlapping ranges endemic to Florida rosemary scrub on the Lake Wales Ridge. All three species have low levels of genetic variation, comparable to or lower than those generally reported for rare plants with restricted geographic ranges. Liatris ohlingerae has more than twice the expected heterozygosity of the other two species, with little population differentiation. In contrast, Hypericum cumulicola has highly differentiated populations with little apparent interpopulation gene flow and heterozygote deficiencies indicative of inbreeding. Eryngium cuneifolium, the species with the narrowest range and fewest populations, has intermediate values for genetic parameters. Although the three species have narrow and overlapping geographic ranges and similar habitat specificity, we discuss how optimal conservation of each species differs.     

Carbohydrate storage in five resprouting Florida scrub plants across a fire chronosequence

Most research analyzing nonstructural carbohydrate (NSC) concentrations on resprouter species in fire-controlled ecosystems has concentrated on how NSC concentrations recover immediately after fire. However, we know little of the effect of long periods without fire on NSC concentrations. In order to assess the effect of different periods of time-since-fire on resprouter species, we studied carbohydrate concentrations (total [NSC], soluble sugars [SS] and nonsoluble sugars [NSS]) in five resprouting species with contrasting trends of abundance across a chronosequence of time-since-fire (0.5-40 yr) in Florida. Carbohydrate concentrations were highest in species with specialized reserve organs. [SS] was mainly explained by factors related to plant size, whereas time-since-fire was the main factor explaining [NSS]. Changes in [NSS] and [NSC] were correlated with the time-since-fire abundance patterns. Variation in [NSS] carbohydrates can be related to the structural development of vegetation, with only those species capable of accessing full light able to accumulate carbohydrates, whereas subordinate plants show reductions in the [NSS] carbohydrate fractions. In areas with long intervals between fires, this carbohydrate reduction could affect subsequent postfire resprouting vigour, although this remains to be confirmed.     

Polymorphic microsatellite markers for the Florida scrub lizard (Sceloporus woodi)

The Florida scrub lizard (Sceloporus woodi) is one of a suite of species restricted to Florida scrub, a threatened ecosystem. We characterized eight microsatellite loci from scrub lizards based on screening of 75–91 individuals per locus. Polymorphism was high (8–20 alleles per locus). Observed and expected heterozygosities ranged from 0.32–0.83 and 0.77–0.91, respectively. These markers will be useful for population‐level analyses and can contribute to a genetic foundation for conservation strategies for this endemic species.     

Strong fungal specificity and selectivity for algal symbionts in Florida scrub Cladonia lichens

Symbiosis is a major theme in the history of life and can be an important force driving evolution. However, across symbioses, it is difficult to tease apart the mechanisms that structure the interactions among potential partners. We used genetic similarity and frequency-based methods to qualitatively and quantitatively examine the patterns of association among several co-occurring Cladonia lichen fungi and their algal photobionts in six disjunct Florida scrub sites. The patterns of association were described by the degree of specificity, i.e. the phylogenetic range of associated partners, and of selectivity, i.e. the frequency of association among partners. Six fungal species associated with only one algal internal transcribed spacer clade, with the remaining two fungi being associated with two algal clades. In all cases, the fungi associated in unequal frequencies with the observed algal photobiont genotypes within those clades--suggesting that both specificity and selectivity were higher than expected. Fungal species can be grouped into three significantly different specificity classes: photobiont specialists, intermediates and generalists. In contrast to the pronounced specificity for photobionts among fungal species, the different Florida scrub sites do not harbour distinct photobiont pools, and differential photobiont availability cannot explain the patterning of lichen associations at this spatial scale. Therefore, we conclude that fungal specificity and selectivity for algal photobionts are major factors in determining the local composition of symbiotic partnerships.     

Gap ecology in Florida scrub: Species occurrence,diversity and gap properties

Questions: Studies of gap effects have been conducted mainly in forests. We studied gap ecology in a pyrogenic Ceratiola ericoides (Florida rosemary) dominated shrubland and asked: How do gap size and the frequency of large gaps change across the fire chronosequence? Do larger gaps differ from smaller gaps in vegetation structure or species diversity? Are effects of gaps independent of, or dependent upon, time‐since‐fire? Are larger gaps refugia for herbs and subshrubs? Location: Archbold Biological Station, Lake Wales Ridge, south‐central Florida, USA. Methods: We investigated plant species occurrence and diversity in 805 gaps (areas free of shrubs taller than 50 cm) in 28 fire‐dependent Florida rosemary scrub sites. We collected quantitative cover data in a subset of seven sites. Results: Gap area distribution was lognormal. The largest gaps occurred throughout all but the longest time‐since‐fire intervals. Gaps were smallest in the longest unburned site but otherwise did not show strong patterns across the fire chronosequence. Species diversity measures increased with increasing gap area, with herbaceous diversity increasing with both gap area and bare sand. Herb diversity (H') decreased with time‐since‐fire. Larger gaps are refugia for some species. Of 14 species occurring in 25–75% of gaps, 13 had increased occupancy with increasing gap area, and gap area was the strongest predictor of occupancy for seven species of herbs and shrubs. Time‐since‐fire was the strongest predictor of occupancy for five species, including four ground lichens that increased with time‐since‐fire. Conclusions: Community structure within Florida scrub gaps is influenced by gap size, which in turn is affected by fire, the dominant ecological disturbance. We present a conceptual model that considers both gap size and time‐since‐fire as drivers of community structure and herbaceous plant diversity in Florida scrub. Because gap properties (independently of fire) have strong influences on species assemblages in Florida rosemary scrub gaps, fire management should consider the number and size of gaps across the landscape.     

Evaluating long-term introduction success of the Florida scrub endemic Crotalaria avonensis (Fabaceae) using a decade of demographic data

Introductions are a critical tool in the recovery of many imperiled species, yet adequate evaluation and development of best practices has lagged. Importantly, long-term post-introduction data are typically lacking, as well as suitable comparisons to wild populations to provide a baseline against which to assess performance. Here, we report on three experimental introductions of Crotalaria avonensis (Fabaceae), a federally endangered perennial herb that is narrowly endemic to scrub of the Lake Wales Ridge in peninsular Florida, U.S.A. We synthesize 10 years of post-introduction monitoring at both the introduced and a nearby, protected wild population to (1) develop best practices for conservation, and (2) evaluate the success of the introduction. First, our study identified best practices that included using transplants propagated from stem cuttings, as well as several factors that may increase seed germination such as habitat choice, seed burial, and litter addition. Second, during the 10 years following the introduction, population density in the introduced population was higher than in a nearby protected, wild population, and a comparison of vital rates revealed that this result was due to relatively high clonal and seedling recruitment rates in the introduced population. Furthermore, the source population, which occurred on unprotected lands, precipitously declined during this time period, further highlighting the importance of safeguarding plants from that population. We report that a new, growing population of C. avonensis has been established to date, with important implications for the species' conservation as well as how introductions are evaluated.     

Mating systems and limits to seed production in two Dicerandra mints endemic to Florida scrub

We used hand-pollination experiments to test the mating systems of and evaluate limits to seed production in two federally listed endangered plants endemic to the Lake Wales Ridge in Florida, USA: Dicerandra frutescens Shinners ssp. frutescens Huck and D. christmanii Huck and Judd (Lamiaceae). Both are nonclonal, short-lived perennials found in gaps created by disturbance (e.g., fire, roads) in Florida scrub. We found that both species require pollen and insect visitation to produce seeds. We detected pollinator limitation of seed production in D. christmanii but not D. frutescens ssp. frutescens, which we suggest is a function of time-since-disturbance or gap size rather than intrinsic differences between the two species. Both species are self-compatible. Inbreeding depression reduced seed set by 60% in D. frutescens ssp. frutescens but did not occur in D. christmanii. We conclude that pollinator limitation (in fire-suppressed populations of both species) and inbreeding depression (in D. frutescens ssp. frutescens) have the potential to limit seed production in these seed-dependent, rare species. Appropriate fire management should mitigate both of these risks, by maintaining large populations and conditions attractive to pollinators. Although these two species are very similar in reproductive biology, comparisons with other Florida scrub endemics and with rare plants in general suggest that potential threats to conservation via reproductive biology are difficult to predict, depending on combinations of ecology, life-history, and phylogenetic history.     

Elevated CO2 increases nitrogen fixation and decreases soil nitrogen mineralization in Florida scrub oak

We report changes in nitrogen cycling in Florida scrub oak in response to elevated atmospheric CO₂ during the first 14 months of experimental treatment. Elevated CO₂ stimulated above-ground growth, nitrogen mass, and root nodule production of the nitrogen-fixing vine, Galactia elliottii Nuttall. During this period, elevated CO₂ reduced rates of gross nitrogen mineralization in soil, and resulted in lower recovery of nitrate on resin lysimeters. Elevated CO₂ did not alter nitrogen in the soil microbial biomass, but increased the specific rate of ammonium immobilization (NH₄⁺ immobilized per unit microbial N) measured over a 24-h period. Increased carbon input to soil through greater root growth combined with a decrease in the quality of that carbon in elevated CO₂ best explains these changes. These results demonstrate that atmospheric CO₂ concentration influences both the internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosystem nitrogen mass (nitrogen fixation and nitrate leaching) in Florida coastal scrub oak. If these changes in nitrogen cycling are sustained, they could cause long-term feedbacks to the growth responses of plants to elevated CO₂. Greater nitrogen fixation and reduced leaching could stimulate nitrogen-limited plant growth by increasing the mass of labile nitrogen in the ecosystem. By contrast, reduced nitrogen mineralization and increased immobilization will restrict the supply rate of plant-available nitrogen, potentially reducing plant growth. Thus, the net feedback to plant growth will depend on the balance of these effects through time.     

Fragmented landscapes, habitat specificity, and conservation genetics of three lizards in Florida scrub

Dry, sandy scrub habitats of the Floridapeninsula represent naturally fragmentedremnants of xeric ecosystems that werewidespread during the Pliocene and earlyPleistocene. This habitat is characterized byhigh endemism, and distribution of genetic andevolutionary diversity among scrub ``islands' isof compelling interest because Florida scrub israpidly disappearing under human development. We compare range-wide diversity inmitochondrial cytochrome b sequences forthree scrub-associated lizards with contrastinglevels of habitat specificity. All speciesshow strong geographic partitioning of geneticdiversity, supporting the hypothesis that scrubfauna is highly restricted by vicariantseparations. The mole skink (Eumecesegregius), the least habitat specific, has thelowest phylogeographic structure among thelizards (_st = 0.631). The mtDNAgeneology for E. egregius is not entirelyconcordant with the five recognized subspeciesand supports a link between populations incentral Florida (E. e. lividus) and theFlorida Keys (E.e. egregius) rather thana previously proposed affiliation betweennorthern and southern populations. The Floridascrub lizard (Sceloporus woodi) is themost habitat specific of the lizards and hasthe strongest phylogeographic structure (_st = 0.876). The sand skink (Neosepsreynoldsi) falls between the moleskink and scrub lizard in terms of habitatspecificity and phylogeographic structure (_st = 0.667). For all three species,networks of mtDNA haplotypes coalesce on twocentral ridges that contain the oldest scrub. The geographic structure and deep evolutionarylineages observed in these species have strongimplications for conservation, includingstrategies for translocation, reserve design,and management of landscape connectivity.     

Competitive abilities of three narrowly endemic plant species in experimental neighborhoods along a fire gradient

We conducted field experiments manipulating lichens, shrubs, and herbs along a time-since-fire gradient and assessing effects on three endemic herbaceous species of Florida scrub: Eryngium cuneifolium, Hypericum cumulicola, and Polygonella basiramia. Responses included seed germination, survival, biomass, and fecundity. Transplants into recently burned patches generally had higher survival, larger biomass, and greater reproductive output than transplants into long-unburned patches. Open areas and sites near oaks frequently were more favorable than sites near Florida rosemary. Ground lichens did not affect germination but increased mortality rate of seedlings. Neighboring small shrubby and herbaceous species did not affect the performance of these species. Of the three species, naturally occurring E. cuneifolium were farthest from large shrubs, and their microhabitats had the least ground lichens and shrubs. Eryngium cuneifolium and H. cumulicola are capable of forming persistent seed banks and their recruitment after fire depends mostly on these dormant seeds. Polygonella basiramia relies on seed dispersal and immediate seed germination to colonize recently burned patches. Management for these species should involve variable fire regimes to allow all three species to persist along with many other scrub endemics.     

Zooplankton-trophic state relationships in some north and central Florida lakes

In a survey of eight lake systems located in north-central Florida, total zooplankton abundance showed a strong positive correlation (r²=0.87, a=0.01) with trophic state. Zooplankton abundance averaged 1.0 × 10⁵ organisms · m^–2 in oligotrophic systems and up to 8.2 × 10⁵ organisms · m^–2 in the eutrophic systems. Seasonal variations in total abundance were greatest in the eutrophic lakes where rotifers dominated and periodically produced sharp population peaks (approaching 2.0 × 10⁶· m^–2). In contrast, the more oligotrophic systems had relatively stable levels of total abundance and were dominated by copepods. Diversities of the major taxa in the lakes were variable with one to three species of copepods, zero to four species of cladocera, and two to seven species of rotifers dominant at any one time. Planktonic cladoceran communities were often composed of only one or two species. Low cladocera diversity in these subtropical systems was suggestive of increased predation pressure on this group of crustaceans. A comparison of the total crustacean abundance in the Florida systems to those of some of the Great Lakes indicated that lower standing crops of crustacean zooplankton in the Florida lakes may be a response to both predation and temperature.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.     

Fire-mediated effects of shrubs, lichens and herbs on the demography of Hypericum cumulicola in patchy Florida scrub

Understanding the effect of disturbance and interspecific interactions on population dynamics and availability of suitable habitats for colonization and growth is critical for conservation and management of endangered species. Hypericum cumulicola is a narrowly endemic, small perennial herb virtually restricted to open areas of well-drained white sand in Florida rosemary scrub, a naturally patchy community that burns about every 20–80 years. Over 1 year (September 1994 to September 1995) we evaluated variation in survival, growth and fecundity among 1214 individuals in 14 rosemary scrub patches of different sizes (0.09–1.85 ha) and fire histories (2, 8–10, and >20 years since the last fire). Fire kills aboveground individuals of H. cumulicola, but new individuals were present a year after fire. Recruitment decreased in patches more than a decade post-fire. Survival, annual height growth rate, and fecundity (number of flowers and fruits) were higher in recently burned patches. Scrub patch size did not affect these demographic variables. Survival was positively associated with the presence of conspecifics and negatively related to proximity to the dominant shrub Florida rosemary (Ceratiola ericoides), prior reproductive output, and ground lichen cover. Since H. cumulicola and other herbaceous species in the rosemary scrub depend on sporadic fires to decrease interference of shrubs and ground lichens, its persistence may be threatened by fire suppression. Received: 4 December 1996 / Accepted: 5 June 1997     

Patterns of reproductive effort with time since last fire in Florida scrub plants

Abstract. In periodically burned ecosystems, fire frequency may be an important selective pressure for the evolution of plant reproductive allocation patterns. We evaluated this hypothesis for Florida (USA) scrub plants by developing three models of reproductive effort with time since last fire given assumptions concerning seed dormancy and seedling establishment. We then examined reproductive effort of five woody, resprouting shrubs at sites representing nine times since last fire (ranging from 0–64 yr). All species showed significant patterns with time since fire in percentage of stems reproductive and fruit production. Stems of all species needed to attain a minimum size before flowering. Four species had the greatest level of reproductive effort (fruit biomass/above-ground biomass) within 5 yr post-fire and best fit the Early Peak Model of reproductive effort (i.e. between-fire seedling recruitment or seed dormancy). A fifth species best fit the Broad Peak Model (i.e. immediate post-fire seedling establishment), peaking in reproductive effort at 7 yr post-fire. Both of these models are based on somewhat variable fire-return intervals, suggesting that the frequency of scrub fires may have been too unpredictable to select for reproductive allocation patterns precisely reflecting particular fire-return intervals. Early peaks in post-fire reproductive effort may be a bet-hedging strategy to allow for greater chances of seedling establishment and survival.     

Modeling the effect of fire on the demography of <Emphasis Type="Italic">Dicerandra frutescens</Emphasis> ssp. <Emphasis Type="Italic">frutescens</Emphasis> (Lamiaceae), an endangered plant endemic to Florida scrub

Managing populations, either for conservation, harvesting, or control, requires a mechanistic or semi-mechanistic understanding of population dynamics. Here, we investigate how time-since-fire affects demographic transitions in an endangered plant, Dicerandra frutescens ssp. frutescens (Lamiaceae), which is specialized to gaps created by fire. We used a hierarchical Bayesian model to estimate transition probabilities (i.e., the elements of population projection matrices) as a function of time-since-fire and random effects, from 13 years of data on marked individuals in five populations. Using a standard Bayesian criterion to compare models, we find that death becomes increasingly probable and progression increasingly improbable with time-since-fire. The magnitude of some of the time-since-fire effects is substantial: death is 3–5 times more likely for flowering plants >6 years versus 3–6 years post-fire, 3-step progression is almost 7 times less likely, and large flowering plants are more than 6 times more likely to stop flowering. These insights inspire new hypotheses about the underlying cause of decline with time-since-fire, and how it can be managed. Our approach can be used by others who wish to model the effect of an exogenous factor on demography, while rigorously accounting for uncertainty and variability. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of natural habitat fragmentation on an endemic scrub lizard (Sceloporus woodi): an historical perspective based on a mitochondrial DNA gene genealogy

The Florida scrub lizard, Sceloporus woodi, is endemic to scrub habitat patches along the central portion of the Florida peninsula and xeric coastal regions. Scrub ecosystems are the patchily distributed remnants of previously widespread habitats formed during the Pleiocene and early Pleistocene. Scrub lizards appear to have limited dispersal capabilities due to high habitat specificity and low mobility. To assess the population structure and phylogeography of S. woodi, 135 samples were collected from 16 patches on five major ridges in Florida, USA. Analysis of 273 bp of mitochondrial DNA (mtDNA) cytochrome b reveals a very strong geographic distribution of genetic diversity. Haplotype frequencies are significantly different in 63 of 66 comparisons between patches. With one exception, samples from the five major ridges are characterized by fixed differences in haplotype distribution and deep evolutionary separations (3-10%). Fixed genetic differences were also observed between northern and southern segments of several ridges. Analysis of molecular variance (AMOVA) shows an estimated 10.4% total genetic variation within patches, 17.5% among patches (within ridges), and 72.1% among ridges. This strong population structure among patches within ridges indicates that the distribution of S. woodi is tightly linked to sandy scrub habitat and that the discontinuous distribution of scrub habitats significantly inhibits dispersal and gene flow. Phylogeographic analyses indicate a pattern of dispersal down the Florida peninsula during the late Pliocene-early Pleistocene, followed by habitat fragmentation and variant isolation events. Therefore, the deep genetic structuring among scrub lizard populations on separate ridges is attributed to ancient isolation events induced by a shift from dry (xeric) to wet (mesic) conditions on the Florida peninsula. These findings indicate that some scrub lizard populations have persisted in isolation for time frames in excess of 1 Myr, providing a case history on the genetic consequences of habitat fragmentation.     

Microhabitat distribution of two Florida scrub endemic plants in comparison to their habitat-generalist congeners

Habitat-specialist species may be restricted to a narrower range of microhabitats than habitat-generalist species. We addressed this hypothesis by comparing microhabitats of two pairs of congeners that differ in habitat specificity and co-occur in one distinct habitat type, Florida rosemary scrub. We characterized microhabitats of rosemary scrub specialists, Polygonella basiramia and Lechea cernua, their habitat-generalist congeners, Polygonella robusta and Lechea deckertii, and random points in the rosemary scrub habitat. Plants of both habitat specialists occurred in microhabitats with significantly more bare sand than plants of habitat-generalist species and random points. Plants of all four species occurred in microhabitats that were farther from dominant shrubs, Ceratiola and Quercus spp., than random points. Seedlings of both habitat specialists grew larger in bare sand microhabitats, whereas ground lichens and litter did not affect seedling growth of the habitat generalists. As the time since fire increases, bare sand cover decreases, Ceratiola density increases, Quercus density remains constant, and shrubs become taller. Physical characteristics, such as soil temperature, soil carbon, and soil moisture, differ slightly with respect to microhabitat. Our results suggest that P. basiramia and L. cernua are specialized on bare sand microhabitats that characterize their preferred habitat, rosemary scrub. Microhabitat specialization may limit the distribution of these rare species.     

Stomatal acclimation to increased CO2 concentration in a Florida scrub oak species Quercus myrtifolia Willd

Native scrub‐oak communities in Florida were exposed for three seasons in open top chambers to present atmospheric [CO₂] (approx. 350 μmol mol^?1) and to high [CO₂] (increased by 350 μmol mol^?1). Stomatal and photosynthetic acclimation to high [CO₂] of the dominant species Quercus myrtifolia was examined by leaf gas exchange of excised shoots. Stomatal conductance (g_s) was approximately 40% lower in the high‐ compared to low‐[CO₂]‐grown plants when measured at their respective growth concentrations. Reciprocal measurements of g_s in both high‐ and low‐[CO₂]‐grown plants showed that there was negative acclimation in the high‐[CO₂]‐grown plants (9–16% reduction in g_s when measured at 700 μmol mol^?1), but these were small compared to those for net CO₂ assimilation rate (A, 21–36%). Stomatal acclimation was more clearly evident in the curve of stomatal response to intercellular [CO₂] (c_i) which showed a reduction in stomatal sensitivity at low c_i in the high‐[CO₂]‐grown plants. Stomatal density showed no change in response to growth in high growth [CO₂]. Long‐term stomatal and photosynthetic acclimation to growth in high [CO₂] did not markedly change the 2·5‐ to 3‐fold increase in gas‐exchange‐derived water use efficiency caused by high [CO₂].