Markwith, Scott

Melaleuca quinquenervia is an Australian tree, an aggressive invader of South Florida ecosystems, and has impacted over 100,000 acres of wetlands with many documented deleterious effects on native ecosystems. Millions of dollars are spent each year on management. The most rapid and cost-effective approach to date is the delivery of broadcast aerial herbicide application via helicopter, though long-term effects of this indiscriminate approach on native vegetation communities is poorly understood. We experimentally examined the effects of broadcast herbicides on uninvaded sawgrass plots in comparison to clip treatments and controls which showed that while clipped plots quickly recovered toward pre-treatment dominance, herbicide plots remained highly dissimilar and showed little to no recruitment even after 36 weeks. We also examined untreated Melaleuca stands to assess relationships between invasion severity and canopy cover using a generalized linear model with a beta distribution. Basal area, number of stems, and the interaction between basal area and number of stems was significantly related to canopy cover. Finally, we surveyed transects through aerially-treated Melaleuca stands (7 years post-treatment) separated into zones of dense infestation, sparse infestation, and untreated marsh. We compared differences in microtopography, invasion severity, and water quality to quantify changes in the physical environment brought about by both invasion and aerial treatment relative to the surrounding marsh. Additionally, we used percent cover abundance of vascular plant species in plots to compare vegetation communities between zones.

We collected, with FWC, taxa inventory and numerical abundance data at three sites, a restoration concurrent with sampling, an older completed restoration, and an unimproved reference site, from 2014 to 2018 in the Central Lake Worth Lagoon, Florida. We examined effects in response to estuary habitat restoration and water quality on nekton food web structure among sites over time. A binary matrix of plausible interactions among trophic species, classified by size, was used to produce 51 individual food webs and nine trophic structure metrices within the R: Package Cheddar. Interactions of site and restoration, i.e., pre- vs. post-restoration samples, were found to be not significant in repeated-measures ANOVAs for each food web metric. Random forest analysis only identified Secchi depth as an important predictor of food web generality. Our findings suggest that generality and Secchi depth are inversely correlated and relatively stable within the Central Lake Worth Lagoon sites.

The objective of this research was to study the impacts of large USSE facilities on wildlife movement corridors and habitat connectivity in Florida to identify important habitat patches and movement corridors significant for potential Florida panther (Puma concolor coryi) dispersal, conservation, and recovery. Large carnivores (such as Florida panther) have often been examined as conservation umbrellas for large-scale connectivity planning due to their extensive spatial requirements (Beier et al., 2006, Thorne et al., 2006). In addition, Florida panther is relatively well-studied species that have been listed as endangered under the US Endangered Species Act for over 40 years, due to habitat fragmentation and reduction. Habitat suitability was compared before and after the installation of the USSE facilities using RandomForest model developed by Frakes and Knight (in prep). The connectivity study focused on comparing current density and effective resistance (resistance distance) before and after the installations of USSE facilities and was conducted using Circuitscape 4.0. The impacts on habitat connectivity were the most substantial in the areas where the USSE facilities were installed on or around wildlife corridors, near focal areas, and in large clusters. The study has identified important linkages and new pathways that animals may try to take in order to bypass the facilities. The study has also shown that installation of USSE facilities in areas not suitable as habitat for Florida panthers, but still permeable or semi-permeable (e.g., agricultural lands), can substantially impact connectivity between focal areas.

The objective of this research was to examine bottlenose dolphin (Tursiops truncatus) habitat use in the Indian River Lagoon (IRL) based on monthly relocation of photo-identified individuals, prey availability and environmental factors from 2003-2015. We focused on the variation of spatial and temporal abiotic and biotic factors and their influence on bottlenose dolphin habitat use patterns. Harbor Branch Oceanographic Institute (HBOI) conducted monthly photo-identification surveys along the length of the IRL and GPS locations of photographed dolphins were collected at the time of surveying. Stratified random samples of prey and environmental variables were collected monthly by the Florida Fish and Wildlife Conservation Commission (FWC) as part of the Fisheries-Independent Monitoring (FIM) program. Kernel density estimation was used to determine the magnitude-per-unit area of dolphins across a continuous raster surface of the IRL by wet and dry seasons each year, the values of which were used as a response variable in Classification and regression tree (CART) analyses with FIM fish community and environmental factors as predictors. Understanding how dolphins respond to environmental factors over time in the IRL could be used to predict future responses in estuaries and prioritize conservation and restoration actions.

The red imported fire ant, Solenopsis invicta, is native to South America and was
introduced to Alabama in the 1930s. This predatory species rapidly spread throughout the
southeastern US and parts of the West Indies, causing serious ecological and economic impacts.
Solenopsis invicta is known to attack the eggs and hatchlings of ground nesting birds and
reptiles. The ants also swarm into sea turtle nests attacking hatchlings and diminishing their
chance for survival. This study is part of a larger research that aimed to survey the distribution of
ants at a sea turtle nesting beaches in South Florida and St. Croix, USVI. This particular study
was conducted in Boca Raton, Florida. Besides providing a baseline dataset on ant species
distribution in the area, this study also aimed at validating the survey methodology by finding
consistency in the distribution over multiple days surveyed. The results indicate that, although
more detailed surveys would produce more thorough results, we can state that the methodology
is consistent in determining species distribution.

Invasion of exotic species is a global threat to native species, biological diversity, and ecological restoration projects. Pomacea maculata is a macrophyte herbivore often misidentified with one of the world’s most invasive and destructive exotic snail, Pomacea canaliculata, but has a broader geographical distribution and climate tolerance, and greater egg production. This research examines whether the exotic P. maculata and native Pomacea paludosa occupy identical vegetation communities, mechanisms of interference competition, grazing impact differences on Vallisneria americana and to develop an exploratory agent based model. This model uses historical and present data to project how differences between species in life history and grazing patterns can potentially impact South Florida ecosystems. This model examined how P. maculate invasion of South Florida could affect two of the Central Everglades Planning Project’s main environmental restoration goals: function of key vegetative communities and
conservation of endangered or threatened species.

Pomacea maculata is invading Florida’s freshwater ecosystems. P. maculata is potentially competing with native Pomacea paludosa. However very little work has looked at the consumption behavior to Vallisneria americana. V. Americana, a restoration plant used by resource managers provides important habitat to nursery species. This study examines P. maculata and P. paludosa’s rate of physical, herbivory, and total damage on V. americana. Our results show P. maculata and P. paludosa demonstrate an average rate of physical damage of 2.5 cm/hr and 1.2 cm/hr, herbivory rates of 1.8 cm/hr and 0.2 cm/hr and total physical damage rates of 4.2 cm/hr and 1.4 cm/hr respectively; and with t-values of 0.180, 0.006, and 0.024 respectively. This study illustrates P. maculata herbivory is significantly greater compared to P. paludosa herbivory, and total damage rates but not physical damage. Resource managers need to consider these higher rates when planning to use V. Americana.

The exotic apple snail Pomacea maculata appears to be gradually extending its range and increasing its density through much of south Florida. As a consequence, there is increasing interest in understanding its life history. One difficulty encountered in studying P. maculata is that it lays large, multilayered clutches of very small eggs that are impossible to count without disaggregating the egg mass; which results in the loss of viability. Using a previously described dis-aggregation technique, we weighed, dis-aggregated, photographed, and counted 70 egg masses of P. maculata collected from various locations in Lake Okeechobee. Using the resulting mass and egg numbers we developed an algorithm that reliably relates clutch mass to the number of eggs in a clutch, allowing the estimation of the number of eggs in a clutch without impacting the eggs’ viability and paving the way for investigations into studies on fecundity, hatching rate, etc.