Dave Jenkins | University of Central Florida (original) (raw)

Papers by Dave Jenkins

1. Allometric scaling of net primary production (NPP) with plant biomass (B) is important to ecol... more 1. Allometric scaling of net primary production (NPP) with plant biomass (B) is important to ecological carbon dynamics and energetics. Metabolic theory predicts a nonlinear power law for NPP scaling, based on fractal vascular systems, resulting in a linear model when using log NPP/log B axes that are standard in allometry. Alternatively, two other hypotheses predict nonlinear models for log-transformed data, with potential tipping points. Size-based competition may cause a quadratic curve as larger plants limit NPP by smaller plants. More inclusively, the plant adaptive strategies hypothesis predicts a sigmoidal curve to represent those same competitive effects, plus stress and ruderal adaptations that maintain relatively low NPP in habitats that are abiotically limiting or disturbed. 2. We evaluated all three hypotheses for terrestrial vascular plants, using information theoretic model selection based on the Akaike Information Criterion (AICc). Published data (N = 709) were organised in subsets according to reported organisational level and plant growth form. Alternative curves were compared for a general model (using all data) and per subset. Potential tipping points were estimated using segmented regression. 3. The plant adaptive strategies hypothesis was supported in general (AICc weight = 1Á00) and via internal consistency for five of six subsets (86% of data). Competition was supported as affecting NPP at greater B, where quadratic and sigmoidal models often coincided. Only non-woody assemblages most plausibly fit a power law model, perhaps related to sparse data at lowest B. 4. Synthesis. Adaptive strategies and corresponding environmental conditions appear to constrain terrestrial net primary production scaling relative to metabolic theory's ideal. Moreover, tipping points in general nonlinear net primary production scaling (at c. 38 and 360 g m À2 B) indicate thresholds for rapid changes in net primary production given changing B that occurs via changing climate, human appropriation and land use.

As land is converted to agriculture (e.g., pastures), natural vegetation is repeatedly disturbed,... more As land is converted to agriculture (e.g., pastures), natural vegetation is repeatedly disturbed, creating various levels of habitat alteration in which flowering plants and pollinators (e.g., bees) interact. Community structure of flowering plants, bees, and flower-bee interactions may each respond to disturbance, but potentially in different ways or magnitudes. We studied flowering plants, bees, and their interactions across four mechanical disturbance levels in and near Archbold Biological Station, Florida (USA) for one year, using repeated sampling with standard techniques in replicated plots. Data were analyzed for community structure, flower-bee interactions and bipartite network structure. Over 7500 flowering plants (81 species) and almost 5000 bees (48 species) were sampled, representing N80% of estimated species richness. Disturbance altered available flower diversity and both shifted and simplified compositions of floral and bee communities. Importantly, the number of foraging bee species did not decrease with disturbance but fewer bee species interacted with flowers given greater disturbance , indicating that disturbance reduced successful foraging. Interaction networks became simpler with disturbance , and the non-native European honey bee (Apis mellifera) became more dominant as disturbance intensity increased. Flower-bee interactions were most sensitive to disturbance. For some native bees, anthropogenic disturbance may contribute to ecological trap conditions and drive long-term diversity patterns. Attention to interaction networks will help land managers identify plant species to conserve and restore flowering plants that are vital to native pollinator communities.

1. Pasture management intensity, livestock grazing and prescribed fire are three widespread agric... more 1. Pasture management intensity, livestock grazing and prescribed fire are three widespread agricultural practices that affect small, isolated wetlands, but few studies have investigated their individual and interactive effects. Pasture management intensity refers to the degree of human alteration of grassland, ranging from intensively managed pastures planted with introduced forage, fertilizer/lime additions and artificial drainage to semi-natural pastures with mixed native and non-native vegetation, no fertilizer/lime additions and little or no artificial drainage. 2. We examined individual and interactive effects of these three agricultural practices on individual , isolated wetlands using a replicated, full-factorial experiment on 40 entire wetlands in south Florida, USA. Wetlands were embedded in two pasture management intensities: intensively managed and semi-natural. 3. After three years of treatment initiation, vegetation of wetlands released from grazing and unburned embedded in semi-natural pastures had significantly lower evenness and coefficient of conservatism scores compared to wetlands released from grazing and burned, grazed unburned wetlands and grazed burned wetlands in the same pasture management intensity. For wetlands embedded in intensively managed pastures, evenness and coefficient of conservatism scores did not differ among treatments. 4. Release from grazing increased abundance of the native, weedy herb, Eupatorium capillifolium. 5. Grazing interacted with prescribed fire to affect shrub abundance and non-native richness; relative abundance of shrubs and non-native richness were greater in wetlands released from grazing and burned and did not differ among burn treatments in grazed wetlands. Interactive effects, especially three-way interactions, were uncommon and not as important as differences between the two pasture management intensities. 6. Synthesis and applications. Vegetation diversity and floristic quality of wetlands embedded in intensively managed pastures resisted common restoration management techniques such as release from grazing and prescribed fire, at least in the short term. In contrast, removing all top-down disturbances from wetlands embedded in semi-natural grasslands can negatively affect vegetation species diversity and floristic quality. Future studies should examine how intensity and seasonality of grazing and prescribed fire affect wetland vegetation, and track long-term responses to evaluate lag effects.

Human-aided transport is responsible for many contemporary species introductions, yet the contrib... more Human-aided transport is responsible for many contemporary species introductions, yet the contribution of human-aided transport to dispersal within non-native regions
is less clear. Understanding dispersal dynamics for invasive species can streamline mitigation efforts by targeting routes that contribute disproportionally to spread. Because of its limited natural dispersal ability, rapid spread of the Asian tiger mosquito (Aedes albopictus) has been attributed to human-aided transport, but until now, the relative roles of human-aided and natural movement have not been rigorously
evaluated. Here, we use landscape genetics and information-theoretic model selection to evaluate 52 models representing 9240 pairwise dispersal paths among sites across the US range for Ae. albopictus and show that recent gene flow reflects a combination of natural and human-aided dispersal. Highways and water availability facilitate dispersal at a broad spatial scale, but gene flow is hindered by forests at the current distributional limit (range edge) and by agriculture among sites within the mosquito’s native climatic niche (range core). Our results show that highways are important to
genetic structure between range-edge and range-core pairs, suggesting a role for human-aided mosquito transport to the range edge. In contrast, natural dispersal is dominant at smaller spatial scales, reflecting a shifting dominance to natural movement two decades after introduction. These conclusions highlight the importance of (i) early intervention for species introductions, particularly those with readily dispersed dormant stages and short generation times, and (ii) strict monitoring of commercial shipments for transported immature stages of Ae. albopictus, particularly towards the
northern edge of the US range.

Limnology has been greatly influenced by The lake as a Microcosm (Forbes, 1887), which described ... more Limnology has been greatly influenced by The lake as a Microcosm (Forbes, 1887), which described a holistic focus on the internal machinations of singular, island-like aquatic ecosystems. I consider three persistent influences of The lake as a Microcosm: as an organizing paradigm for the teaching of limnology relative to its practice; the idea that inland waters are like islands, and the replicability of types of inland waters. Based on inspection of recent peer-reviewed literature and 32 limnology texts, we teach limnology according to Forbes but do not practice it in that holistic context. Instead, we practice limnology as aquatic ecology. Based on novel analyses of species-area relationships for 275 inland waters and 392 islands, inland waters are more like continental habitat patches than islands; the island metaphor is poetic but not accurate. Based on a quantitative review of beta diversity (40 l data sets representing 10,576 inland waters and 26 data sets representing 1529 terrestrial sites), aquatic systems are no more replicable than are terrestrial systems; a typological approach to limnology is no more justified than it is in terrestrial systems.

I conclude that a former distinction between limnology and aquatic ecology no longer applies, and that we should define limnology as the ecology of inland waters. Also, we should not consider lakes and rivers as islands that represent other systems of the same type, but should consider them as open, interactive habitat patches that vary according to their geology and biogeography. I suggest modern limnology operates according to 3 paradigms, which combine to form 3 broad limnological disciplines and establish a basis for a plural, interactive view of lakes and rivers as microcosms. This model of modern limnology may help better connect it to ecology and biogeography and help limnology be even more relevant to science and society.

Urbanization is a leading cause of species loss in the United States because of habitat destruct... more Urbanization is a leading cause of species loss in
the United States because of habitat destruction and frag-
mentation. Wetlands can be affected by urbanization and the
condition of wetlands can be compared across land use
categories. Cypress domes are isolated wetlands dominated
by cypress (Taxodium distichum) and often remain in urban
areas. The purpose of this study was to quantify the effects
of urbanization on cypress dome number, size and spatial
pattern through two decades of rapid urbanization in
Orlando, Florida, a large city in the southeastern US. Over
3,000 cypress domes, in a region typical of urban growth in
the cypress range, were identified in images from 1984.
Over a 20-year period, 26 % were destroyed or degraded
(i.e., no longer cypress-dominated) and almost half in man-
aged forests were degraded, destroyed, or became sur-
rounded by urban or agricultural land uses. The smallest
and largest cypress domes were lost, leaving only medium-
sized wetlands and decreasing landscape-level diversity.
Despite the fact that these wetlands are common and par-
tially protected by legislation, cypress in isolated wetlands
may be at risk from urbanization.

1. Land use (e.g. urbanization, agriculture, natural lands management) may directly affect popul... more 1. Land use (e.g. urbanization, agriculture, natural lands management) may directly affect
populations by habitat loss and fragmentation, and indirectly by altering conditions needed
for reproductive success. The effects of urbanization are especially pronounced for popula-
tions that remain among urbanized areas, but they are difficult to detect in long-lived species.
2. We evaluated the effects of urbanization on the recruitment of cypress (Taxodium disti-
chum), a long-lived coniferous tree that dominates isolated wetlands in Orlando, Florida,
USA, a rapidly urbanizing region. Cypress requires saturated but not flooded soils to germi-
nate, and seedlings are easily out-competed in the absence of fire. We hypothesized that
urbanization has altered the hydrology and fire regimes, leading to biological inertia and
reduced cypress recruitment relative to managed forest and ranchland.
3. We found low cypress recruitment in urban areas, but surprisingly in managed forest as
well. Many cypress populations in managed forest were bounded by fire breaks which prevent
upland fires from burning into the wetlands. Ranchland had significantly more recruitment
than urban and managed forest, and these wetlands did not have fire breaks.
4. In urban lands, the effects of urbanization were delayed. Cypress recruitment initially
occurred near the edge of wetlands where hydrological conditions were most favourable, but
virtually stopped at 20 years post-urbanization. Cypress recruitment also occurred near the
edge of the wetlands in managed forests and ranchlands and was higher in larger wetlands.
5. Synthesis and applications. Urbanization is associated with the eventual reproductive fail-
ure of cypress and in the absence of management practice changes, cypress recruitment may
cease in many additional wetlands. If past urbanization rates continue, 80–90% of cypress
populations in isolated wetlands in the path of urban sprawl could permanently cease recruit-
ment in 100 years. Reducing urban sprawl and introducing prescribed fire in managed-forest
cypress domes could mitigate this effect and conserve reproduction of this long-lived, domi-
nant tree species and the diversity of the wetlands they typify.

Aim Community ecologists often compare assemblages. Alternatively, one may compare species distri... more Aim Community ecologists often compare assemblages. Alternatively, one may compare species distributions among assemblages for macroecological comparisons of species niche traits and dispersal abilities, which are consistent with metacommunity theory and a regional community concept. The aim of this metaanalysis is to use regressions of ranked species occupancy curves (RSOCs) among diverse metacommunities and to consider the common patterns observed.

Both biogeography and ecology seek to understand the processes that determine patterns in nature,... more Both biogeography and ecology seek to understand the processes that determine patterns in nature, but do so at different spatial and temporal scales. The two disciplines were not always so different, and are recently converging again at regional spatial scales and broad temporal scales. In order to avoid confusion and to hasten progress at the converging margins of each discipline, the following papers were presented at a symposium in the International Biogeography Society's 2011 meeting, and are now published in this issue of the Philosophical Transactions of the Royal Society B. In a novel approach, groups of authors were paired to represent biogeographic and ecological perspectives on each of four topics: niche, comparative ecology and macroecology, community assembly, and diversity. Collectively, this compilation identifies points of agreement and disagreement between the two views on these central topics, and points to future research directions that may build on agreements and reconcile differences. We conclude this compilation with an overview on the integration of biogeography and ecology.

Although ecology and biogeography had common origins in the natural history of the nineteenth cen... more Although ecology and biogeography had common origins in the natural history of the nineteenth century, they diverged substantially during the early twentieth century as ecology became increasingly hypothesis-driven and experimental. This mechanistic focus narrowed ecology's purview to local scales of time and space, and mostly excluded large-scale phenomena and historical explanations. In parallel, biogeography became more analytical with the acceptance of plate tectonics and the development of phylogenetic systematics, and began to pay more attention to ecological factors that influence large-scale distributions. This trend towards unification exposed problems with terms such as 'community' and 'niche,' in part because ecologists began to view ecological communities as open systems within the contexts of history and geography. The papers in this issue represent biogeographic and ecological perspectives and address the general themes of (i) the niche, (ii) comparative ecology and macroecology, (iii) community assembly, and (iv) diversity. The integration of ecology and biogeography clearly is a natural undertaking that is based on evolutionary biology, has developed its own momentum, and which promises novel, synthetic approaches to investigating ecological systems and their variation over the surface of the Earth. We offer suggestions on future research directions at the intersection of biogeography and ecology.

Isolation by distance (IBD) has been a common measure of genetic structure among populations and ... more Isolation by distance (IBD) has been a common measure of genetic structure among populations and is based on Euclidean distances among populations. Whereas IBD does not incorporate geographic complexity (e.g. dispersal barriers, corridors) that may better predict genetic structure, a new approach (landscape genetics) joins landscape ecology with population genetics to better model genetic structure. Should IBD be set aside or should it persist as the most simple model in landscape genetics? We evaluated the status of IBD by collecting and analyzing results of 240 IBD data sets among diverse taxa and study systems. IBD typically represented a low proportion of variance in genetic structure (mean r 2 00.22) in part because many studies included relatively few populations (mean 011). The number of populations studied (N) was asymptotically related to IBD significance; a study with 9 populations has only 50% probability of significance, while one with!23 populations will have 90% probability of significance. Surprisingly, ectothermic animals were significantly (p00.0018) more likely to have significant IBD than endotherms, which suggests a metabolic basis underlying gene flow rates. We also observed marginally significant effects on IBD significance for a) taxa in general and b) dispersal modes within actively-dispersing endotherms. Other factors analyzed (genetic markers, genetic distances, habitats, active or passive dispersal, plant growth form) did not significantly affect IBD, likely related to typical N. For multiple reasons we conclude that IBD should continue as the simplest reference standard against which all other, more complex models should be compared in landscape genetics research.

Different management regimes imposed on similar habitat types provide opportunities to investigat... more Different management regimes imposed on similar habitat types provide opportunities to investigate mechanisms driving community assembly and changes in species composition. We investigated the effect of pasture management on vegetation composition in wetlands with varying spatial isolation on a Florida cattle ranch. We hypothesized that increased pasture management intensity would dampen the expected negative effect of wetland isolation on native species richness due to a change from dispersal-driven community assembly to niche-driven assembly by accentuated environmental tolerance. We used native plant richness, exotic plant richness and mean coefficient of conservatism (CC) to assess wetland plant assemblage composition. Sixty wetlands were sampled, stratified by three levels of isolation across two pasture management intensities; semi-native (less intensely managed; mostly native grasses, never fertilized) and agronomically improved (intensely managed, planted with exotic grasses, and fertilized). Improved pasture wetlands had lower native richness and CC scores, and greater total soil phosphorus and exotic species coverage compared to seminative pasture wetlands. Increased wetland isolation was significantly associated with decreases in native species richness in semi-native pasture wetlands but not in improved pasture wetlands. Additionally, the speciesÁarea relationship was stronger in wetlands in improved pastures than semi-native pastures. Our results indicate that a) native species switch from dispersal-based community assembly in semi-native pastures to a species-sorting process in improved pastures, and b) recently-introduced exotic species already sorted for more intensive management conditions are primarily undergoing dispersal-based community assembly. That land-use may alter the relative importance of assembly processes and that different processes drive native and exotic richness has implications for both ecosystem management and restoration planning.

Escherichia coli and Serratia liquefaciens, two bacterial spacecraft contaminants known to replic... more Escherichia coli and Serratia liquefaciens, two bacterial spacecraft contaminants known to replicate under low atmospheric pressures of 2.5 kPa, were tested for growth and survival under simulated Mars conditions. Environmental stresses of high salinity, low temperature, and low pressure were screened alone and in combination for effects on bacterial survival and replication, and then cells were tested in Mars analog soils under simulated Mars conditions. Survival and replication of E. coli and S. liquefaciens cells in liquid medium were evaluated for 7 days under low temperatures (5, 10, 20, or 30°C) with increasing concentrations (0, 5, 10, or 20%) of three salts (MgCl 2 , MgSO 4 , NaCl) reported to be present on the surface of Mars. Moderate to high growth rates were observed for E. coli and S. liquefaciens at 30 or 20°C and in solutions with 0 or 5% salts. In contrast, cell densities of both species generally did not increase above initial inoculum levels under the highest salt concentrations (10 and 20%) and the four temperatures tested, with the exception that moderately higher cell densities were observed for both species at 10% MgSO 4 maintained at 20 or 30°C. Growth rates of E. coli and S. liquefaciens in low salt concentrations were robust under all pressures (2.5, 10, or 101.3 kPa), exhibiting a general increase of up to 2.5 orders of magnitude above the initial inoculum levels of the assays. Vegetative

Eastern mosquitofish (Gambusia holbrooki) are native to the southeastern United States but notori... more Eastern mosquitofish (Gambusia holbrooki) are native to the southeastern United States but notoriously invasive elsewhere, and are aggressive predators in ecosystems they inhabit. Information on dispersal behavior is needed to better understand mosquitofish spread upon introduction and potential means to mitigate that spread. We experimentally tested the effects of shallow water depths (3-24 mm) and obstacles (leaf litter) on mosquitofish dispersal behavior, plus a range of conditions relevant to field situations. Mosquitofish dispersed significantly faster in deeper water (p < 0.001) but some dispersed in only 3 mm water depth (i.e., one-half average body depth). Wetland and upland leaf litter at natural densities strongly interfered with mosquitofish dispersal behavior. Based on our results, introduced mosquitofish spread rapidly given unimpeded dispersal corridors (e.g., mowed ditches), and may do so at rates >800 m/day. Also, consistent lack of sexual dimorphism in dispersal behavior indicates that mosquitofish spread is not strongly dependent on female poeciliid reproductive biology. Our results support designation of mosquitofish as highly invasive and suggest that barriers to mosquitofish spread must obstruct dispersal pathways as shallow as 3 mm depth.

Aim The aim of this study is to answer the questions: (1) do small organisms disperse farther tha... more Aim The aim of this study is to answer the questions: (1) do small organisms disperse farther than large, or vice versa; and (2) does the observed pattern differ for passive and active dispersers? These questions are central to several themes in biogeography (including microbial biogeography), macroecology, metacommunity ecology and conservation biology.

Mercury contamination in fish is a serious public health concern that contrasts with other health... more Mercury contamination in fish is a serious public health concern that contrasts with other health benefits of eating fish. Like most US states, Illinois has monitored fish mercury contamination for decades to warn the public of mercury exposure risks by consuming fish. Has this monitoring program been effective in detecting public mercury exposure risks? I analyzed fish mercury contamination data from Illinois inland lakes ; >2,300 samples, 18 fish species, 149 lakes) and found that: (a) sampling and analyses have been severely limited since 1985; (b) sampling effort varied widely among lakes and species, and (c) trends and spatial patterns were confused by this variability. As a result of a severely limited and nonstrategic monitoring program, public mercury exposure risks via Illinois fish consumption remain unclear, despite much effort over many years. Illinois monitors fewer fish per angler than many US states, but is not alone in this regard. Illinois should resurrect and redesign its fish contaminant monitoring program to one that strategically and systematically assesses human mercury exposure risk. Other US states and nations may also benefit from similar retrospective examinations of monitoring programs intended to protect public health.

Alternative models of community assembly emphasize regional, stochastic, dispersal-based processe... more Alternative models of community assembly emphasize regional, stochastic, dispersal-based processes or local, deterministic, niche-based processes. Community ecology's historical focus on local processes implicitly assumes that local processes surpass regional processes over time or across space to derive nonrandom metacommunity structure (i.e., a quorum effect). Quorum effects are expected late in succession among nearby sites, whereas quorum effects are not expected early in succession among distant sites. I conducted a metaanalysis of zooplankton data sets encompassing time scales of one to thousands of years and spatial scales of ,1 m to thousands of kilometers. Species co-occurrence analyses statistically evaluated presence/absence patterns relative to random patterns obtained with Monte Carlo null models. A series of weighted analyses was conducted and alternative randomization algorithms and null models were evaluated.

Before European settlement, 23% of Illinois (3.2 million of 14 million ha) was covered by wetland... more Before European settlement, 23% of Illinois (3.2 million of 14 million ha) was covered by wetlands. It is estimated that 90% of those wetlands were lost during conversion of the landscape to agriculture and urban use. Champaign County was one of the most extensively drained counties in Illinois, with 39-60% of original county area estimated to have been drained. Current and future efforts to conserve and restore wetlands would benefit from information on the number and distribution of former wetlands. We used GIS to estimate the spatial extent, density, pattern, and sizes of former and extant depressional wetlands in Champaign County. We derived several models of former wetlands; all models used hydric soils but varied by using Digital Raster Graphics (DRG), 30-m Digital Elevation Models (DEM), or Digital Orthophotography Quarter Quadrangles (DOQ). We also combined the DRG and DEM models, and we conducted visual field surveys for saturated or ponded conditions to test the models. The DRG model was conservative: it identified fewer and larger wetlands than the DEM model (the DOQ model was judged inadequate). Depending on the model selected, we estimated that 1077-4090 depressional wetlands formerly existed in the county, and that 78.6-91.6% were drained, accounting for 1108-2777 ha of lost wetland habitat in Champaign County alone. Thus, depressional wetlands accounted for the vast majority of historical wetland loss and should be a priority for wetland restoration efforts. Spatial pattern among wetlands also changed: an organism adapted to the former landscape had Ͼ50% probability of reaching another wetland within 260 m: today that same species faces a 7.8% probability at that distance. The modern landscape of Champaign County (and others like it) poses potential risk for remaining wetland metapopulations, and GIS models of precise former wetlands locations can be a valuable initial tool for wetland conservation and restoration efforts.