Invasive species are cited as a major threat to native community composition and biodiversity throughout the world. Some recent studies have focused on whether invasive species are the drivers or passengers of change in degraded systems. A strongly-interactive community is supposed to resist invasion by all but the most strong invasive competitors (`drivers') which can establish there without the aid of disturbance and actively reduce the abundance of natives. A weakly-interactive community, impaired by some anthropogenic disruption, is invasible by weaker exotics which are merely `passengers' of the habitat degradation that is more constraining to natives. Though competitive and disturbance-adapted species fit into this model, there is no correlate for species with superior toleration of stress. Systems with high degrees of natural abiotic stress are weakly-interactive and as a result may be invasible by an exotic `tolerator' in the same way that anthropogenically-weak systems are invasible by passengers. Dolomite prairie, differentiated from typic tallgrass prairie by its shallow soils, represents a relatively stressful system. A study of its plant community composition and relationships to environmental variables was done to get a better understanding of the natural abiotic drivers of composition. Compositional patterns were most closely associated with the soil depth gradient. Exotic Poa species were by far the most frequent invaders, a finding more typical of Great Lakes alvars than of typic tallgrass prairie of which the dolomite prairie is a subset. I hypothesized that Poa species dominated dolomite prairie via the tolerator model. In a series of removal treatments, I determined that Poa is neither a driver nor a tolerator, but a passenger of environmental degradation. My results suggest that historic anthropogenic degradation rather than specific competitive ability is a common explanation for exotic dominance on the landscape today. More empirical work needs to be conducted in other stressful (particularly relatively undisturbed) systems to further investigate the tolerator model.

A common injury type associated with vessel groundings on coral reefs is generation of coral rubble. As a substrate rubble is dynamic and can be mobilized by normal wave agitation, causing secondary damage to surviving corals and preventing coral larvae and invertebrates from surviving. Typical rubble management options include offsite removal and onsite stabilization using artificial materials. Sponges show promise as a restoration tool for rubble stabilization, especially sponges that are known to have rapid regeneration rates, low mortality, and the capability to quickly form attachment points to natural and artificial substrates. As an effective restoration tool a sustainable source of sponge is required in order to minimize impact on natural populations. The purpose of this project is to evaluate the feasibility of sponge propagation for use as a restoration material following groundings on coral reefs in Biscayne National Park, FL. If small sponge fragments could be collected from donor sponges and propagated on artificial growout structures (i.e. nurseries) a sustainable source of sponge fragments could be maintained for future restoration activities. If feasible, this technique would create a continually growing sponge source that would require a single harvest, reducing pressure on the local sponge populations. Fragments of four species of native sponges, Aplysina fulva¸ Amphimedon compressa, Aplysina cauliformis, and Iotrochota birotulata, were harvested and attached to artificial growout structures composed of PVC rods and cement paver tiles. Fragment necrosis, attachment, sponge retention (persistence throughout the study), complexity, and growth rates for all four species were recorded monthly for one year. Two different PVC types were utilized to compare attachment material effects on growth. Donor sponges were monitored to assess recovery and growth after harvesting, and intact sponges in the natural population were also monitored as a control. Transplanted fragments had the highest retention of any treatment (96-100% of fragments remained), growth rates ranging from 105% to 424%, low necrosis rates, and all but one species increased in complexity. There was no significant difference in sponge growth on different PVC types or between sites. Within one month all donor wounds inflicted by harvest were completely healed, and by the end of the study donors had significantly higher growth rates than the control treatment, ranging from 400% to 781% of initial sponge volume. Donor sponges also had low necrosis rates, but were less complex than controls. This is a promising, practical and low cost method, and based on these results, is a feasible way of producing sponges for us in restoration, with little negative impact on the natural populations.