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W.F. Loftus

Publications and source records attributed to W.F. Loftus.

23 records · Page 2Linked to original sources
USGS2000

Distribution and relative abundance of the crayfishes Procambarus alleni (Faxon) and P. fallax (Hagen) in southern Florida

The Everglades crayfish (Procambarus alleni Faxon) is the only species reported from Everglades National Park (ENP) and Big Cypress National Preserve (BICY). However, we identified a second species, Procambarus fallax (Hagen), from those locations. Reexamination of archived samples showed that P. fallax had been collected as early as 1985 but had been misidentified or overlooked; therefore, we provide methods for distinguishing live and preserved specimens of these morphologically similar species. Species relative abundance varied predictably with hydroperiod (length of inundation) both in recent collections and in archived samples. Procambarus fallax relative abundance was highest in sites characterized by long hydroperiod and prolonged inundation, whereas P. alleni was the lone species in short hydroperiod marshes.

Wetlands↗
USGS1998

Long-term hydrologic effects on marsh plant community structure in the southern Everglades

Although large-scale transformation of Everglades landscapes has occurred during the past century, the patterns of association among hydrologic factors and southern Everglades freshwater marsh vegetation have not been well-defined. We used a 10-year data base on the aquatic biota of Shark Slough to classify vegetation and describe plant community change in intermediate- to long-hydroperiod Everglades marshes. Study area marsh vegetation was quantitatively grouped into associations dominated by 1) Cladium jamaicense , 2) a group of emergents including Eleocharis cellulosa, Sagittaria lancifolia , and Rhyncospora tracyi , 3) taxa associated with algal mats ( Utricularia spp. and Bacopa caroliniana ), and 4) the grasses Panicum hemitomon and Paspalidium geminatum . During the decade evaluated, the range of water depths that characterized our study sites approached both extremes depicted in the 40-year hydrologic record for the region. Water depths were near the long-term average during the mid-1980s, declined sharply during a late 1980s drought, and underwent a prolonged increase from 1991 through 1995. Overall macrophyte cover varied inversely with water depth, while the response of periphyton was more complex. An ordination analysis, based on plant species abundance, revealed that study area vegetation structure was associated with hydrologic patterns. Marsh plant community structure showed evidence of cyclic interannual variation corresponding to hydrologic change over the decade evaluated. Lower water depths, the occurrence of marl substrates, and high periphyton cover were correlated. These factors contributed to reduced macrophyte cover in portions of the study area from which water had been diverted.

Florida↗
USGS1997

Modeling fish dynamics and effects of stress in a hydrologically pulsed ecosystem

Many wetlands undergo seasonal cycles in precipitation and water depth.This environmental seasonality is echoed in patterns of production of fishbiomass, which, in turn, influence the phenology of other components of thefood web, including wading birds. Human activities, such as drainage orother alterations of the hydrology, can exacerbate these natural cycles andresult in detrimental stresses on fish production and the higher trophic levels dependent on this production. In this paper we model theseasonal pattern of fish production in a freshwater marsh, with specialreference to the Everglades/Big Cypress region of southern Florida.The model illustrates the temporal pattern of production through theyear, which can result in very high densities of fish at the end of ahydroperiod (period of flooding), aswell as the importance of ponds and other deep depressions, both as refugia and sinks during dry periods. The model predicts that: (1) there is an effective threshold in the length of the hydroperiod that must beexceeded for high fish-population densities to be produced, (2) large,piscivorous fishes do not appear tohave a major impact on smaller fishes in the marsh habitat, and (3) therecovery of small-fish populations in the marsh following a major droughtmay require up to a year. The last of these results is relevant toassessing anthropogenic impacts on marsh production, as these effectsmay increase the severity and frequency of droughts.

Journal of Aquatic Ecosystem Stress and Recovery↗