Florida Scrub Habitat Research Articles

Seedling Establishment in Natural and Experimental Florida Scrub Gaps

PETRU, M. AND E. S. MENGES (Archbold Biological Station, P.O. Box 2057, Lake Placid, FL 33862). Seedling establishment in natural and experimental Florida scrub gaps. J. Torrey Bot. Soc. 130: 89-99. 2003.-Gaps are often important microhabitats for recruitment of herbaceous plants. In the Florida scrub, fires create gaps by top-killing resprouting shrubs. These natural gaps are aboveground gaps (without aboveground vegetation) that may also be complete gaps (if belowground roots and rhizomes are absent). Within three types of gaps (natural gaps, experimental aboveground and experimental complete gaps), we studied seedling recruitment and survival of spontaneous species and seven sown herbs for two years. We created aboveground gaps by clipping vegetation and complete gaps by removing shrub roots and rhizomes. These gaps occurred in two Florida scrub habitats: rosemary scrub and scrubby flatwoods. We also explored factors that can affect recruitment patterns in gaps, such as soil moisture, root water retention and light availability. In addition, we tested effects of supplemental watering on sown seeds in the field since drought in 2000 and 2001 suppressed natural seedling recruitment. The watering treatment increased recruitment in all types of gaps. Over half of all gaps were colonized, but there were few seedlings. Recruitment was highest in watered, complete gaps in scrubby flatwoods, where the soil moisture levels were higher and light levels lower than in the other gap types. Seedlings of a single spontaneously recruited species (Lechea deckertii) were more abundant than sown species. Locally common gap specialists were more abundant than generalists. Because many of these gap specialists are endangered plant species, understanding how disturbances create microsites for their regeneration is critical for conservation and management of the Florida scrub ecosystem. In small-scale conservation projects, artificially created gaps may substitute for post-fire gaps when prescribed burning is impossible.

Fragmentation of Florida scrub in an urban landscape

The Florida scrub community is considered a biodiversity hotspot due to the high degree of endemism and the number of species restricted to a few counties or fragments. Florida scrub habitat is officially listed as an imperiled ecoregion of global importance because it is a geographically restricted habitat with a high diversity of rare and endemic flora. This study examines landscape metrics and plant species richness of scrub in Pinellas County, which is the most densely populated county in Florida and once contained large areas of Florida scrub. Landscape metrics on scrub area, historic xeric upland area, naturally vegetated upland area within proximity, isolation indices, disturbance, and soils were collected for the 20 largest and best remaining fragments of scrub in Pinellas County from Geographic Information Systems map layers, Digital Ortho Quarter Quadrangles, and field validation. Landscape metrics were compared with three categories of species richness: scrub species richness, obligate scrub species richness, and richness of species listed as threatened or endangered. All categories of species richness in remaining Florida scrub fragments in Pinellas County were significantly associated with area of remaining scrub habitat. Site elevation was associated with obligate scrub species richness and degree of disturbance was associated with higher species richness for listed species. We conclude that large areas of scrub in higher elevated uplands and active management in the form of prescription burning will be needed to ensure the persistence of a number of endemic scrub specific species within remaining fragments.

Duplex auditory distance assessment in a small passerine bird ( Pipilo erythrophthalmus )

Eastern towhees, Pipilo erythrophthalmus, (Emberizidae, Passeriformes) in Florida estimate source sound-pressure level (SPL; i.e., sound amplitude) and often misjudge speaker distance in the field when vocalization source SPL is varied experimentally. Sound frequencies below ~3.5 kHz attenuate reliably with distance in comparison with higher sound frequencies in Florida scrub habitat. As a result, I predicted that towhees should use SPL as an auditory distance cue when they hear stimuli produced with sound frequencies below ~3.5 kHz but use another cue when they hear stimuli produced with sound frequencies above ~3.5 kHz. Subjects often misjudged speaker distance when approaching playbacks of SPL-altered stimuli produced with sound frequencies below ~3.5 kHz but rarely misjudged speaker distance when played SPL-altered stimuli produced with sound frequencies above ~3.5 kHz. I discuss the possibility that towhees employ a duplex sound localization strategy.

Duplex auditory distance assessment in a small passerine bird and the relationship with sound attenuation and vocalization production

Eastern towhees, Pipilo erythrophthalmus (Emberizidae, Passeriformes, Aves) estimate how loudly conspecific vocalizations are produced using correlated spectral and temporal variables and often misjudge speaker distance in the field when vocalization source sound-pressure level (SPL) is varied experimentally. I demonstrate that towhees often misjudge speaker distance when played SPL altered stimuli produced with sound frequencies below 3.5 kHz but rarely misjudge speaker distance when played SPL altered stimuli produced with sound frequencies above 3.5 kHz. I describe the homogeneous physical-acoustic structure of towhee Florida scrub habitat and demonstrate that sound frequencies below 3.5 kHz attenuate more reliably over distance in comparison with sound frequencies above ∼3.5 kHz (i.e., sound frequencies below 3.5 kHz propagate with less variation in attenuation across sites sampled, several speaker and microphone elevations and between days). Lastly, I describe acoustical measurements obtained from calls produced by 52 caged subjects in the field, which suggest that sound frequencies to each side of 3.5 kHz are produced independently or are otherwise emphasized differently during production. These experiments suggest that auditory distance perception in the towhee might be described as ‘‘duplex’’ and that variation in sound propagation might often mediate a close relationship between vocalization production and auditory perception.

A New Species of Melanoplus (Orthoptera: Acrididae) from an Isolated Upland in Peninsular Florida

A new species of flightless acridid grasshopper, Melanoplus withlacoocheensis n. sp., is described from an isolated upland, the Southern Brooksville Ridge, in west central peninsular Florida. It occurs in open sandhill habitat. It appears to be closely related to Melanoplus rotundipennis Scudder, which is widespread in sandhill and Florida scrub habitats in central and northern peninsular Florida; the species are distinguished by details of the male cerci and genitalia. The new species is one of several species of flightless Melanoplus in Florida whose geographic ranges are small and biogeographically revealing. The new species is the first clear biological indicator of the long-term isolation of the Southern Brooksville Ridge from other uplands, including the Northern Brooksville Ridge.

Effects of Fragmentation on the Richness of Vertebrates in the Florida Scrub Habitat

Structures of habitat fragments interact with autecologies of resident species to produce patterns in taxonomic richness. Understanding this interaction is crucial to habitat conservation. We studied the vertebrates inhabiting fragments of the severely threatened sand pine scrub habitat of interior peninsular Florida. We surveyed 16 scrubs in south—central Florida that were categorized as either “large,” “medium,” or “small.” For each scrub, we determined (1) vegetational structure, (2) vegetational composition, (3) distance to the nearest scrub, (4) distance to the nearest larger scrub, (5) presence/absence of potential “corridor“ habitats between scrubs, (6) types of habitats between scrubs, (7) distance to the nearest permanent water, (8) percent coverage of surrounding habitats, and (9) area reduction over time. The principal methods used to census nonavian taxa were pitfall and double—ended funnel traps, while the principal method for avian taxa was transect surveys. Many of the nine scrub attributes were intercorrelated. Scrub size was the only attribute that correlated strongly with vertebrate richness. Distance, both to permanent water and to the nearest scrub, correlated strongly with nonavian richness after the influence of size was removed, however. We detected significant nestedness, but when the taxon—area relationship was taken into consideration, we could not demonstrate that any taxa were excluded from small scrubs. We constructed joint lists of taxa from various hypothetical “archipelagos” of the 16 individual scrubs, and found that the archipelagos often supported more taxa than large individual scrubs. We found no tendency for small scrubs to be depauperate, in general, and no matter how rare taxa were identified, they were more common than expected in medium and small scrubs, and less common than expected in large scrubs. The mere observation of either a taxon—area relationship or a nested taxonomic composition reveals little about underlying ecological processes. Our detailed analysis leads us to conclude that no evidence indicates the need for single large scrub reserves for resident vertebrates: an archipelago of individually smaller reserves could support at least as many taxa. This conclusion is based solely on the simple presence—absence of taxa in scrubs that were treated as replicates within size categories, however, and consideration of the abundances and distributions of individual taxa, and of the variation among scrubs of similar size, may lead to a different conclusion.