Everglades National Park (Fla.) -- Environmental conditions

Self-organized spatial patterning of microtopographic features is a trademark
characteristic of the Everglades landscape. Anthropogenic modifications to Everglades’
hydrology have reduced and degraded pattern, where ridges occur at higher elevations
and spread into open water sloughs under dryer conditions. Wildfire is an important
ecological force in the central Everglades and may maintain ridge-slough patterning
through reducing ridge size and complexity, and thus preserve habitat heterogeneity. To
investigate fire as a patterning mechanism in the central Everglades I examined the shape
complexity and area distribution of ridges along a chronosequence of time since fire.
Shape complexity did not change following fire, but small and large ridges became more
prominent and eventually spread as time since fire increased, suggesting fire may
maintain ridge area distribution. Documentation of fires’ effect on ridge size will inform
ecosystem and conceptual models detailing the complex interactions that maintain the
Everglades ridge-slough patterning.

Anthropogenic impacts, such as habitat destruction and spread of exotic species,
are contributing to the sixth major extinction event in Earth’s history. To develop
effective management and conservation plans, it is important to understand the ecological
drivers of at-risk populations, assess the ability of a population to adapt to environmental
change, and develop research methods for long-term ecosystem monitoring. I used
wading birds nesting in the Florida Everglades, USA as a model system to address the
challenges of managing and monitoring populations within an ecosystem greatly
impacted by anthropogenic activities. Specifically, my project investigated 1) the prey
selection of wading bird species, and the role of prey and foraging habitat availability on
annual nesting numbers, 2) the ability of using diet change to predict species adaptability
to a rapidly changing environment, and 3) the use of sensory data to provide low-cost,
long-term monitoring of dynamic wetlands. I found that tricolored herons, snowy egrets, and little blue herons consumed marsh fish larger than those generally available across
the landscape. Additionally, number of nests initiated by tricolored herons, snowy egrets,
and little blue herons was strongly correlated with the annual densities of large fish
available within the Everglades landscape. Conversely, number of nests initiated by
wood storks, great egrets, and white ibises was more correlated with the amount of
foraging habitat availability across the nesting season. Wood stork diets changed
considerably since the 1960’s, consisting of mainly sunfish and exotic fish as opposed to
marsh fishes dominant in historical diet studies. Storks also consumed more exotic fish
species than they did historically. This diet plasticity and the species’ ability to exploit
anthropogenic habitats may be conducive to maintaining population viability as storks
experience widespread human-induced changes to their habitat. Sensory-only data
models generated complementary results to models that used site-specific field data.
Additionally, sensory-only models were able to detect different responses between size
classes of fish to the processes that increase their concentrations in drying pools.
However, the degree to which sensory variables were able to fit species data was
dependent upon the ability of sensors to measure species-specific population drivers and
the scale at which sensors can measure environmental change.

Peatlands act as carbon sinks while representing major sources of biogenic gases
such as methane (CH4) and carbon dioxide (CO2), two potent greenhouse gases. Gas
production and release in these peats soils are also influenced by overall warm
temperatures and water table fluctuations due to the naturally shallow water table in the
Florida Everglades. Releases of biogenic gases from Florida Everglades peat soils are not
well understood and the temporal distribution and dynamics are uncertain. The general
objective of this work was geared towards a methodological approach which aimed to
examine the feasibility of capacitance moisture probes to investigate biogenic gas
dynamics in various Florida Everglades peat soils at high temporal resolution. This work
has implications for establishing capacitance moisture probes as a method to monitor gas
dynamics in peat soils at high temporal resolution and better understanding patterns of
gas build-up and release from peat soils in the Everglades.

In south Florida, the Greater Everglades ecosystem supports sixteen species of
wading birds. Wading birds serve as important indicator species because they are highly
mobile, demonstrate flexible habitat selection, and respond quickly to changes in habitat
quality. Models that establish habitat relationships from distribution patterns of wading
birds can be used to predict changes in habitat quality that may result from restoration
and climate change. I developed spatio-temporal species distribution models for the
Great Egret, White Ibis, and Wood Stork over a decadal gradient of environmental
conditions to identify factors that link habitat availability to habitat use (i.e., habitat
selection), habitat use to species abundance, and species abundance (over multiple scales)
to nesting effort and success. Hydrological variables (depth, recession rate, days since
drydown, reversal, and hydroperiod) over multiple temporal scales and with existing
links to wading bird responses were used as proxies for landscape processes that influence prey availability (i.e., resources). In temporal foraging conditions (TFC)
models, species demonstrated conditional preferences for resources based on resource
levels at differing temporal scales. Wading bird abundance was highest when prey
production from optimal periods of wetland inundation was concentrated in shallow
depths. Similar responses were observed in spatial foraging conditions (SFC) models
predicting spatial occurrence over time, accounting for spatial autocorrelation. The TFC
index represents conditions within suitable depths that change daily and reflects patch
quality, whereas the SFC index spatially represents suitability of all cells and reflects
daily landscape patch abundance. I linked these indices to responses at the nest initiation
and nest provisioning breeding phases from 1993-2013. The timing of increases and
overall magnitude of resource pulses predicted by the TFC in March and April were
strongly linked to breeding responses by all species. Great Egret nesting effort and
success were higher with increases in conspecific attraction (i.e., clustering). Wood Stork
nesting effort was closely related to timing of concurrently high levels of patch quality
(regional scale) and abundance (400-m scale), indicating the importance of a multi-scaled
approach. The models helped identify positive and negative changes to multi-annual
resource pulses from hydrological restoration and climate change scenarios, respectively.