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  1. Habitat heterogeneity is a key driver of biodiversity of macroorganisms, yet how heterogeneity structures belowground microbial communities is not well understood. Importantly, belowground microbial communities may respond to any number of abiotic, biotic, and spatial drivers found in heterogeneous environments. Here, we examine potential drivers of prokaryotic and fungal communities in soils across the heterogenous landscape of the imperiled Florida scrub, a pyrogenic ecosystem where slight differences in elevation lead to large changes in water and nutrient availability and vegetation composition. We employ a comprehensive, large-scale sampling design to characterize the communities of prokaryotes and fungi associated with three habitat types and two soil depths (crust and subterranean) to evaluate (i) differences in microbial communities across these heterogeneous habitats, (ii) the relative roles of abiotic, biotic, and spatial drivers in shaping community structure, and (iii) the distribution of fungal guilds across these habitats. We sequenced soils from 40 complete replicates of habitat × soil depth combinations and sequenced the prokaryotic 16S and fungal internal transcribed spacer (ITS) regions using Illumina MiSeq. Habitat heterogeneity generated distinct communities of soil prokaryotes and fungi. Spatial distance played a role in structuring crust communities, whereas subterranean microbial communities were primarily structured by the shrub community, whose roots they presumably interacted with. This result helps to explain the unexpected transition we observed between arbuscular mycorrhiza–dominated soils at low-elevation habitats to ectomycorrhiza-dominated soils at high-elevation habitats. Our results challenge previous notions of environmental determinism of microbial communities and generate new hypotheses regarding symbiotic relationships across heterogeneous environments. 
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    Free, publicly-accessible full text available November 2, 2024
  2. Abstract

    Advances in remote sensing technologies offer new means to monitor habitats of importance on large scales. Florida rosemary scrub is one such threatened habitat, found in patches across the landscape in relatively elevated areas, and is often characterized by shrub‐less areas (gaps) among the dominant shrubs, which provide favorable microhabitats for many endemic and endangered plants and animals. However, gaps are difficult and time‐consuming to characterize, especially across large areas, using traditional ground‐based field methods. We developed and tested a method for rapidly classifying gaps using an unmanned aerial vehicle (UAV or drone). Aerial data were collected by a UAV‐mounted camera in April 2018, and stratified, random ground surveys to verify UAV data were conducted March through April 2018 at Archbold Biological Station in south‐central Florida, USA. We used mosaicked and georeferenced digital surface and terrain models to calculate vegetation height across 33 rosemary scrub sites (~230,000 m2at 0.064 m2pixel resolution). Gaps were defined as >1 m2areas where vegetation height was <10 cm. We found that gap areas from UAV models and field surveys were significantly correlated across varying gap sizes, times‐since‐fire, and relative elevations. We also observed a significant decrease in mean gap area and percent gap space with increasing time‐since‐fire, a pattern consistent with smaller‐scale, ground‐based sampling, and a marginally significant increase in gap area with relative elevation. This remote sensing method lends itself to better exploration of how gap areas, their spatiotemporal patterns, and associated fire history, elevation, soil, and other geographic data affect structural vegetation dynamics across the landscape. This study illustrates the success of UAV modeling of gap space in Florida rosemary scrub, a result of regional consequence for the southeastern United States, but more broadly, it encourages the use of UAV technology as a tool to enhance traditional field‐based methods in systems globally. As habitat fragmentation and loss become increasingly problematic for the conservation of threatened habitats, understanding these complex spatial dynamics is crucial to the conservation and management of vegetation communities and their biodiversity.

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  3. Abstract

    Seed bank, seed dispersal and historical disturbance are critical factors affecting plant population persistence. However, because of difficulties collecting data on these factors they are often ignored.

    We evaluated the roles of seed bank, seed dispersal and historical disturbance on metapopulation persistence ofHypericum cumulicola, a Florida endemic. We took advantage of long‐term demographic data of multiple populations (22 years; ~11 K individuals; 15 populations) and a wealth of information on burn history (1962–present), and habitat attributes (patch specific location, elevation, area and aggregation) of a system of 92 patches of Florida rosemary scrub. We used previously developed integral projection models to assess the relative ability of simulations with different levels of seed dormancy for recently produced and older seeds and different dispersal kernels (including no dispersal) to predict regional observed occupancy and plant abundance in patches in 2016–2018. We compared a simulation with this model using historical burn history to 500 model simulations with the same average fire regime (using a Weibull distribution to determine the probability of ignition) but with random ignition years.

    The most likely model had limited dispersal (mean = 0.5 m) and the highest dormancy (field estimates × 1.2 %) and its predictions were associated with observed occurrences (67% correct) and densities (20% of variance explained). Historical burn synchrony among neighbouring patches (skewness in the number of patches burned by year = 1.79) probably explains the higher densities predicted by the simulation with the historical fire regime compared with predicted abundances after simulations using random ignition years (skewness = 0.20 +SE= 0.01).

    Synthesis.Our findings demonstrate the pivotal role of seed dormancy, dispersal and fire history on population dynamics, distribution and abundance. Because of the prevalence of metapopulation dynamics, we should be aware of the significance of changes in the availability and configuration of suitable habitat associated with human or non‐human landscape changes. Decisions on prescribed fires (or other disturbances) will benefit from our knowledge of consequences of fire frequency, but also of location of ignition and the probability of fire spread.

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