Steven C. Pennings

University of Houston, Houston, Texas, United States

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Publications (115)362.95 Total impact

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    Wenwen Liu · Keith Maung-Douglass · Donald R. Strong · Steven C. Pennings · Yihui Zhang ·
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    ABSTRACT: 1.Phenotypic variation plays an important role in successful plant invasions. The spread of invasive species over large geographic ranges may be facilitated if plants can match their phenotype to local abiotic conditions. Spartina alterniflora, native to the United States, was introduced into China in 1979 and has spread over 19ᵒ of latitude along the eastern coast of China.2.We studied patterns in vegetative growth and sexual reproduction of S. alterniflora at 22 sites at 11 geographic locations over a latitudinal gradient of ~2000 km from Tanggu (39.05 °N, high latitude) to Leizhou (20.90 °N, low latitude) in China. We further evaluated the basis of phenotypic differences by growing plants from across the range in a common garden for 2 growing seasons.3.We found distinct latitudinal clines in plant height, shoot density, and sexual reproduction across latitude. Some traits exhibited linear relationships with latitude; others exhibited hump-shaped relationships. We identified correlations between plant traits and abiotic conditions such as mean annual temperature, growing degree days, tidal range, and soil nitrogen content. However, geographic variation in all but one trait disappeared in the common garden, indicating that variation largely due to phenotypic plasticity. Only a slight tendency for latitudinal variation in seed set persisted for two years in the common garden, suggesting that plants may be evolving genetic clines for this trait.4.Synthesis. The rapid spread of Spartina alterniflora (S. alterniflora) in China has probably been facilitated by phenotypic plasticity in growth and reproductive traits. We found little evidence for the evolution of genetic clines in China, even though these exist for some traits in the native range. The considerable variation among clones, within provenances, that persisted in the common garden suggests a potential for the evolution of geographic clines in the future. Low fecundity of low latitude S. alterniflora populations in China might result in a slower spread at low latitudes, but S. alterniflora is likely to continue to spread rapidly at high latitudes in China and into the Korean peninsula.This article is protected by copyright. All rights reserved.
    Journal of Ecology 10/2015; DOI:10.1111/1365-2745.12487 · 5.52 Impact Factor
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    Merryl Alber · Steven C. Pennings · James T. Hollibaugh ·

    Limnology and Oceanography Bulletin 09/2015; DOI:10.1002/lob.10063
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    ABSTRACT: In general, community similarity is thought to decay with distance; however, this view may be complicated by the relative roles of different ecological processes at different geographical scales, and by the compositional perspective (e.g. species, functional group and phylogenetic lineage) used. Coastal salt marshes are widely distributed worldwide, but no studies have explicitly examined variation in salt marsh plant community composition across geographical scales, and from species, functional and phylogenetic perspectives. Based on studies in other ecosystems, we hypothesized that, in coastal salt marshes, community turnover would be more rapid at local versus larger geographical scales; and that community turnover patterns would diverge among compositional perspectives, with a greater distance decay at the species level than at the functional or phylogenetic levels. We tested these hypotheses in salt marshes of two regions: The southern Atlantic and Gulf Coasts of the United States. We examined the characteristics of plant community composition at each salt marsh site, how community similarity decayed with distance within individual salt marshes versus among sites in each region, and how community similarity differed among regions, using species, functional and phylogenetic perspectives. We found that results from the three compositional perspectives generally showed similar patterns: there was strong variation in community composition within individual salt marsh sites across elevation; in contrast, community similarity decayed with distance four to five orders of magnitude more slowly across sites within each region. Overall, community dissimilarity of salt marshes was lowest on the southern Atlantic Coast, intermediate on the Gulf Coast, and highest between the two regions. Our results indicated that local gradients are relatively more important than regional processes in structuring coastal salt marsh communities. Our results also suggested that in ecosystems with low species diversity, functional and phylogenetic approaches may not provide additional insight over a species-based approach.
    PLoS ONE 05/2015; 10(5):e0127781. DOI:10.1371/journal.pone.0127781 · 3.23 Impact Factor
  • Lena Hübne · Steven C. Pennings · Martin Zimmer ·
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    ABSTRACT: Distinct habitats are often linked through fluxes of matter and migration of organisms. In particular, intertidal ecotones are prone to being influenced from both the marine and the terrestrial realms, but whether or not small-scale migration for feeding, sheltering or reproducing is detectable may depend on the parameter studied. Within the ecotone of an upper saltmarsh in the United States, we investigated the sex-specific movement of the semi-terrestrial crab Armases cinereum using an approach of determining multiple measures of across-ecotone migration. To this end, we determined food preference, digestive abilities (enzyme activities), bacterial hindgut communities (genetic fingerprint), and the trophic position of Armases and potential food sources (stable isotopes) of males versus females of different sub-habitats, namely high saltmarsh and coastal forest. Daily observations showed that Armases moved frequently between high-intertidal (saltmarsh) and terrestrial (forest) habitats. Males were encountered more often in the forest habitat, whilst gravid females tended to be more abundant in the marsh habitat but moved more frequently. Food preference was driven by both sex and habitat. The needlerush Juncus was preferred over three other high-marsh detrital food sources, and the periwinkle Littoraria was the preferred prey of male (but not female) crabs from the forest habitats; both male and female crabs from marsh habitat preferred the fiddler crab Uca over three other prey items. In the field, the major food sources were clearly vegetal, but males have a higher trophic position than females. In contrast to food preference, isotope data excluded Uca and Littoraria as major food sources, except for males from the forest, and suggested that Armases consumes a mix of C4 and C3 plants along with animal prey. Digestive enzyme activities differed significantly between sexes and habitats and were higher in females and in marsh crabs. The bacterial hindgut community differed significantly between sexes, but habitat effects were greater than sex effects. By combining multiple measures of feeding ecology, we demonstrate that Armases exhibits sex-specific habitat choice and food preference. By using both coastal forest and saltmarsh habitats, but feeding predominantly in the latter, they possibly act as a key biotic vector of spatial subsidies across habitat borders. The degree of contributing to fluxes of matter, nutrients and energy, however, depends on their sex, indicating that changes in population structure would likely have profound effects on ecosystem connectivity and functioning.
    Oecologia 03/2015; DOI:10.1007/s00442-015-3271-0 · 3.09 Impact Factor
  • Steven C. Pennings · Brittany D. McCall · Linda Hooper-Bui ·
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    ABSTRACT: Coastal wetlands are important to human well-being and vulnerable to oil spills. Research on biotic effects of oil has been focused on microbes, plants, and benthic invertebrates, neglecting terrestrial arthropods. We review how oil affects terrestrial arthropods in coastal marshes and suggest future research topics. Terrestrial arthropods play important ecological roles in coastal marshes, affecting primary production and decomposition and providing food to terrestrial and marine vertebrates. Some species are pests and disease vectors for humans and livestock. Terrestrial arthropods are sensitive to oil exposure and are suppressed even in lightly oiled sites where plants are not affected. Some arthropods later reinhabit oiled marshes, which demonstrates that portions of the arthropod community may be resilient to oil exposure. However, oil that remains in sediments may affect terrestrial populations for years after the spill. The sensitivity of arthropods to oil exposure makes them useful indicators of marsh health following environmental impacts.
    BioScience 09/2014; 64(9):789-795. DOI:10.1093/biosci/biu118 · 5.38 Impact Factor
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    ABSTRACT: Despite their value, coastal ecosystems are globally threatened by anthropogenic impacts, yet how these impacts are driven by economic development is not well understood. We compiled a multifaceted dataset to quantify coastal trends and examine the role of economic growth in China's coastal degradation since the 1950s. Although China's coastal population growth did not change following the 1978 economic reforms, its coastal economy increased by orders of magnitude. All 15 coastal human impacts examined increased over time, especially after the reforms. Econometric analysis revealed positive relationships between most impacts and GDP across temporal and spatial scales, often lacking dropping thresholds. These relationships generally held when influences of population growth were addressed by analyzing per capita impacts, and when population density was included as explanatory variables. Historical trends in physical and biotic indicators showed that China's coastal ecosystems changed little or slowly between the 1950s and 1978, but have degraded at accelerated rates since 1978. Thus economic growth has been the cause of accelerating human damage to China's coastal ecosystems. China's GDP per capita remains very low. Without strict conservation efforts, continuing economic growth will further degrade China's coastal ecosystems.
    Scientific Reports 08/2014; 4:5995. DOI:10.1038/srep05995 · 5.58 Impact Factor
  • Kazimierz Więski · Steven Pennings ·
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    ABSTRACT: Interactions between plants and herbivores often vary on a geographic scale. Although theory about plant defenses and tolerance is predicated on temporal or spatial variation in herbivore damage, no single study has compared the pattern of herbivory, plant defenses and tolerance to herbivory of a single species across a latitudinal gradient. In 2002–2005 we surveyed replicate salt marshes along the Atlantic coast of the United States from Florida to Maine. At each field site we scored leaves of Iva frutescens for herbivore damage. In laboratory experiments we measured constitutive resistance and induced resistance in I. frutescens from high and low latitude sites along the Atlantic Coast. In another common garden experiment we studied tolerance to herbivory of I. frutescens from various sites. Theory predicts that constitutive resistance should matter more when damage is high, and induced resistance when herbivory is high but variable. In the field, average levels of herbivore damage, and spatial and temporal variation in herbivore damage were all greater at low versus high latitudes, indicating that constitutive as well as induced resistance should be stronger at low latitudes. Consistent with this prediction, constitutive resistance to herbivory was stronger at low latitudes. Induced resistance to herbivores was also stronger at low latitudes: it was deployed faster and lasted longer. Theory also predicts that tolerance to herbivory should be greater where average herbivory damage is greater; however, tolerance to herbivory in Iva did not depend on geographic origin. Our results emphasize the value of considering multiple ways in which plants respond to herbivores when examining geographic variation in plant–herbivore interactions.
    Ecography 03/2014; 37(8). DOI:10.1111/ecog.00498 · 4.77 Impact Factor
  • Hongyu Guo · Kazimierz Więski · Zhenjiang Lan · Steven C. Pennings ·
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    ABSTRACT: Understanding the processes determining community structure is one of the major goals of ecological research. Both deterministic and stochastic processes may shape community structure. The challenge is to understand the relative influence of each type of process across different environmental conditions. We investigated the influence of deterministic and stochastic processes on plant community assembly in tidal marshes across a strong abiotic (salinity) gradient in three estuaries in Georgia, USA using probabilistic Raup–Crick community dissimilarity. Our results indicated that deterministic processes had an increasingly important influence on structuring plant communities in salt and brackish marshes, probably due to high heterogeneity of microhabitats produced by the interplay between abiotic stress and biotic interactions. In contrast, the influence of deterministic processes on plant community assembly decreased in tidal freshwater marshes, suggesting an increasingly important role of stochastic processes in plant community assembly in tidal freshwater marshes, probably due to the higher species richness, higher recruitment from seed, and lower levels of abiotic stress in these habitats. At the estuarine scale (across tidal freshwater, brackish and salt marshes in each estuary), our results suggested that deterministic processes also had a relatively important influence on shaping plant community structure. Our results illustrated that plant community structure in tidal marshes is influenced by both deterministic and stochastic processes, but that the relative influence of these two types of processes varies across estuarine landscapes.
    Oikos 02/2014; 123(2). DOI:10.1111/j.1600-0706.2013.00425.x · 3.44 Impact Factor
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    ABSTRACT: An important recent advance in food web ecology has been the application of theory regarding spatial gradients to studies of the factors that affect animal population dynamics. Building on extensive studies of the Spartina alterniflora food web at the local scale, we hypothesized that geographic variation in S. alterniflora quality is an important bottom‐up control on food web structure and that geographic variation in S. alterniflora quality would interact with the presence of predators and top omnivores to mediate herbivore densities.We employed a four‐factor fully crossed experiment in which we (i) collected plants from high‐ and low‐latitude locations and grew them in a common garden and varied (ii) plant fertilization status (mimicking the plant quality differences due to marsh elevation), (iii) mesopredator density and (iv) omnivore density.Our results suggest that the single most important factor mediating insect herbivore densities is local variation in plant quality – induced in our experiment by fertilization and demonstrated repeatedly as a consequence of marsh elevation.Top‐down effects were generally weak and in those cases where predators did exert a significant suppressing effect on herbivores, that impact was itself mediated by host‐plant characteristics.Finally, despite observed variation in plant quality with latitude, and the separately measurable effects of this variation on herbivores, geographic‐scale variation in plant quality was overwhelmed by local conditions in our experiments.Synthesis. We suggest that a first‐order understanding of variation across large latitudinal ranges in the Spartina alterniflora arthropod food web must begin with local variation in plant quality, which provides strong bottom‐up forcing to herbivore populations. A second‐order understanding of the arthropod food web should consider the role of predation in controlling herbivores feeding on low‐quality plants. Finally, while latitudinal variation in plant quality probably explains some variation in herbivore densities, it is probably more of a response to herbivore pressure than a driver of the herbivore dynamics. Although extrapolating from local to geographic scales presents multiple challenges, it is an essential task in order for us to develop an understanding that is general rather than site‐specific.
    Journal of Ecology 09/2013; 101(5). DOI:10.1111/1365-2745.12137 · 5.52 Impact Factor
  • Hongyu Guo · Yihui Zhang · Zhenjiang Lan · Steven C Pennings ·
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    ABSTRACT: Many species are expanding their distributions to higher latitudes due to global warming. Understanding the mechanisms underlying these distribution shifts is critical for better understanding the impacts of climate changes. The climate envelope approach is widely used to model and predict species distribution shifts with changing climates. Biotic interactions between species, however, may also influence species distributions, and a better understanding of biotic interactions could improve predictions based solely on climate envelope models. Along the northern Gulf of Mexico coast, USA, sub-tropical black mangrove (Avicennia germinans) at the northern limit of its distribution grows sympatrically with temperate salt marsh plants in Florida, Louisiana, and Texas. In recent decades, freeze-free winters have led to an expansion of black mangrove into salt marshes. We examined how biotic interactions between black mangrove and salt marsh vegetation along the Texas coast varied across 1) a latitudinal gradient (associated with a winter-temperature gradient); 2) the elevational gradient within each marsh (which creates different marsh habitats); and 3) different life history stages of black mangroves (seedlings versus juvenile trees). Each of these variables affected the strength or nature of biotic interactions between black mangrove and salt marsh vegetation: 1) Salt marsh vegetation facilitated black mangrove seedlings at their high-latitude distribution limit, but inhibited black mangrove seedlings at lower latitudes; 2) mangroves performed well at intermediate elevations, but grew and survived poorly in high and low marsh habitats; 3) the effect of salt marsh vegetation on black mangroves switched from negative to neutral as black mangroves grew from seedlings into juvenile trees. These results indicate that the expansion of black mangroves is mediated by complex biotic interactions. A better understanding of the impacts of climate change on ecological communities requires incorporating context-dependent biotic interactions into species range models. This article is protected by copyright. All rights reserved.
    Global Change Biology 04/2013; 19(9). DOI:10.1111/gcb.12221 · 8.04 Impact Factor
  • Kazimierz Więski · Steven C. Pennings ·
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    ABSTRACT: Tidal wetlands are threatened by global changes related not only to sea level rise but also to altered weather patterns. To predict consequences of these changes on coastal communities, it is necessary to understand how temporally varying abiotic conditions drive wetland production. In 2000–2011, we conducted annual surveys of Spartina alterniflora biomass in tidal marshes at nine sites in and around the Altamaha river estuary on the coast of Georgia, USA. End of the year live biomass was assessed in the creekbank and midmarsh zones to estimate annual net primary production (ANPP). River discharge was the most important driver of S. alterniflora ANPP, especially in creekbank vegetation. Increased river discharge reduces water column salinity, and this was most likely the proximate driver of increased production. In the midmarsh zone, the patterns were less distinct, although river discharge was again the best predictor, but maximum temperature had similar predictive ability. In contrast to results from terrestrial grasslands, we found no consistent evidence for a sharply delimited critical period for any climate driver in the tidal marsh, which indicates that plant growth was responsive to abiotic drivers at any time during the growing season. Results were broadly consistent across multiple sites within a geographic region. Our results differ from previous analyses of production in S. alterniflora marshes, which either identified oceanic drivers of S. alterniflora production or were unable to identify any drivers, likely because the low-latitude sites we studied were hotter and more affected by river discharge than those in previous studies.
    Ecosystems 04/2013; 17(3):473-484. DOI:10.1007/s10021-013-9732-6 · 3.94 Impact Factor
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    Chuan-Kai Ho · Steven C Pennings ·
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    ABSTRACT: High-latitude plants are often more palatable to herbivores than low-latitude conspecifics. Does increased plant palatability lead to better herbivore performance? Our field and laboratory work investigated (A) whether high-latitude plants have traits indicating that they should be higher-quality foods for herbivores; (B) whether geographic differences in plant quality are more important than local adaptation of herbivores. We studied 3 plant species and 6 invertebrate herbivores in U.S. Atlantic Coast. Past studies had shown high-latitude individuals of these plants are more palatable than low-latitude conspecifics. We documented plant traits and herbivore performance (body size) in the field across latitude. We collected individuals from different latitudes for factorial (plant region x herbivore region) laboratory experiments, examining how herbivore performance was affected by plant region, herbivore region, and their interaction (i.e., local adaptation). Field surveys suggested high-latitude plants were likely of higher quality to herbivores. Leaf nitrogen content in all plant species increased toward high latitudes, consistent with lower leaf C/N and higher leaf chlorophyll content at high latitudes. Furthermore, leaf toughness decreased toward higher latitudes in 1 species. The body size of 4 herbivore species increased with latitude, consistent with high-latitude leaves being of higher quality, while 2 grasshopper species showed the opposite pattern, likely due to life-history constraints. In the laboratory, high-latitude plants supported better performance in 4 herbivore species (marginal in the 5th). The geographic region where herbivores were collected affected herbivore performance in all 6 species; however, the pattern was mixed, indicating a lack of local adaptation by herbivores to plants from their own geographic region. Our results suggest that more-palatable plants at high latitudes support better herbivore growth. Given that geographic origin of either plants or herbivores can affect herbivore performance, the nature of plant-herbivore interactions is likely to change if climate change "reshuffles" plant and herbivore populations across latitude.
    PLoS ONE 03/2013; 8(3):e59829. DOI:10.1371/journal.pone.0059829 · 3.23 Impact Factor
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    Malte Treplin · Steven C Pennings · Martin Zimmer ·
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    ABSTRACT: To add to our understanding of species richness-effects on ecosystem processes, we studied the importance of species complementarity in driving decomposition in a saltmarsh in Georgia, USA. We studied pair-wise interactions of both detritivores and plant litter species and how they affect decomposition rates in an experiment located on the mid-marsh platform. Needle rush, Juncus roemerianus, had 2-3 times higher decomposition rates than cordgrass, Spartina alterniflora, or live oak, Quercus virginiana. Mixing litter types did not promote decomposition rates. Cordgrass decomposition was 1.5-times higher when periwinkles, Littoraria irrorata, were present than in detritivore-free controls. In contrast, neither coffee-bean snails, Melampus bidentatus, nor wharf crabs, Armases cinereum, increased cordgrass decomposition rates. Mixing detritivore species did not increase cordgrass mass loss beyond expected rates from an additive model. We conclude that in this system, species do not act complementarily with each other, but that decomposition rates are controlled by the dominant species of angiosperms and invertebrate detritivores.
    Wetlands 02/2013; 33:83-89. DOI:10.1007/s13157-012-0353-1 · 1.57 Impact Factor
  • Steven C Pennings ·
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    ABSTRACT: A landscape-scale experiment shows that excessive nutrient levels can cause the loss of salt marshes -- a result that was not seen in smaller studies. This illustrates the value of large-scale, long-term studies in ecology. See Letter p.388
    Nature 10/2012; 490(7420):352-3. DOI:10.1038/490352a · 41.46 Impact Factor
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    ABSTRACT: Predation on detritivores is expected to decelerate detritivore-mediated decomposition processes. In field mes-ocosms, we studied whether the decomposition of leaf and needle litter of live oak (Quercus virginiana) and loblolly pine (Pinus taeda), respectively, was affected by saltmarsh detritivores (Gastropoda: Littoraria irrorata and Melampus bidentatus) and predacious omnivores (Decapoda: Armases cinereum) and their interactions. Both crabs and snails alone increased decomposition (mass loss) rates of oak litter, while a combination of both resulted in the same mass loss as in animal-free controls, probably due to crabs feeding on snails rather than litter. Neither crabs nor snails alone affect-ed mass loss of pine litter, but a combination of both signif-icantly increased decomposition rates. Irrespective of the litter type, crabs significantly increased mortality of the snails but gained biomass only on pine litter and only when detritivorous snails were present. Our findings suggest that unidirectional facilitation of omnivorous semi-terrestrial crabs by their detritivorous prey (saltmarsh snails) promotes the decomposition of low-quality (pine) litter. On high-quality (oak) litter, by contrast, negative effects of the predator pre-vail, resulting in a drop of decomposition rates when crabs were present, probably owing to predation on detritivorous snails. Thus, the effects of predator/prey-interactions on decomposition processes are context-dependent and are controlled by resource quality.
    Wetlands 10/2012; 32(5):931-938. DOI:10.1007/s13157-012-0326-4 · 1.57 Impact Factor
  • Kazimierz Wieski · Steven C. Pennings ·
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    ABSTRACT: Background/Question/Methods Global climate changes are altering functioning of the earth’s ecosystems. Tidal saltmarshes are threatened by sea level rise and changes in weather patterns and river discharge. In order to predict the consequences of climate change on coastal communities, we need to understand how climate drivers mediate ecosystem production. In case of the tidal marshes this understanding is currently ambiguous and geographically limited to the central and northern part of the Atlantic coast. In 2000-2011 we conducted annual surveys of Spartina alterniflora biomass in tidal marshes of the coast of Georgia. Plant length was measured at permanent plots established near the creekbank and in the midmarsh zone at 9 sites located over a salinity gradient of the Altamaha river estuary. Data on plant length was converted into biomass using site specific regressions. Spartina alterniflora biomass, air temperature, precipitation, sea level and Altamaha river discharge were analyzed using multilevel modeling. Results/Conclusions Spartina ANPP strongly varied between years: in the creekbank zone biomass was up to 8 times greater in El Nino years as in La Nina years, in the midmarsh zone the difference was up to 4.8 fold. Biomass fluctuations resulted from changes in plant density as well as plant size. River discharge had stronger effects on creekbank than mid-marsh production and local precipitation conversely had stronger effects on mid-marsh than creekbank production. The effects of river discharge were correlated with average salinity at the site, with sites having higher average salinities (closer to the river mouth) being more strongly affected. No effect of sea level on ANPP had been detected. The decrease in salinity in high discharge years was most likely the proximate driver of the increased production. Our results differ from analyses from tidal marshes of the central and northern part of the Atlantic coast which can be due to differences in climate or hydrology and/or reflect differences in statistical and sampling methodology.
    97th ESA Annual Convention 2012; 08/2012
  • Chelse M. Prather · Steven C. Pennings ·
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    ABSTRACT: Background/Question/Methods Efforts to manage grasslands in general, and coastal tallgrass prairie in particular, often focus on managing for native plant diversity, assuming that a diverse plant community will support higher trophic levels that are often conservation targets. This assumption is based upon a prevailing hypothesis in ecology that suggests herbivores should be more diverse and abundant where plants are more diverse and abundant; however, this prevailing hypothesis has led ecologists to overlook other factors that are potentially important to herbivore communities, such as micronutrient concentrations. We used a natural experiment to examine the relative importance of factors affecting herbivore community structure by measuring plant and herbivore biomass and diversity and plant, litter and soil macro- and micro-nutrients across a range of human influence in a coastal tallgrass prairie south of Houston. Results/Conclusions These data show that plant community attributes alone do not adequately predict density or richness of herbivores, but that plant micro-nutrients (specifically calcium) are important in mediating herbivore community structure. Most strikingly, areas with low plant richness and biomass due to high amounts of calcium in soil have grasshopper diversity equal to areas with high plant species richness and biomass. Surprisingly, these areas with low plant richness and biomass had higher grasshopper abundance than areas with high plant richness and biomass. These results suggest that herbivore communities are not regulated solely by plant diversity and abundance, and therefore, managing for grassland plant diversity may not be sufficient to achieve high diversity and density of higher prairie trophic levels.
    97th ESA Annual Convention 2012; 08/2012
  • Hongyu Guo · Steven C Pennings ·
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    ABSTRACT: Oysters are ecosystem engineers in marine ecosystems, but the functions of oyster shell deposits in intertidal salt marshes are not well understood. The annual plant Suaeda linearis is associated with oyster shell deposits in Georgia salt marshes. We hypothesized that oyster shell deposits promoted the distribution of Suaeda linearis by engineering soil conditions unfavorable to dominant salt marsh plants of the region (the shrub Borrichia frutescens, the rush Juncus roemerianus, and the grass Spartina alterniflora). We tested this hypothesis using common garden pot experiments and field transplant experiments. Suaeda linearis thrived in Borrichia frutescens stands in the absence of neighbors, but was suppressed by Borrichia frutescens in the with-neighbor treatment, suggesting that Suaeda linearis was excluded from Borrichia frutescens stands by interspecific competition. Suaeda linearis plants all died in Juncus roemerianus and Spartina alterniflora stands, regardless of neighbor treatments, indicating that Suaeda linearis is excluded from these habitats by physical stress (likely water-logging). In contrast, Borrichia frutescens, Juncus roemerianus, and Spartina alterniflora all performed poorly in Suaeda linearis stands regardless of neighbor treatments, probably due to physical stresses such as low soil water content and low organic matter content. Thus, oyster shell deposits play an important ecosystem engineering role in influencing salt marsh plant communities by providing a unique niche for Suaeda linearis, which otherwise would be rare or absent in salt marshes in the southeastern US. Since the success of Suaeda linearis is linked to the success of oysters, efforts to protect and restore oyster reefs may also benefit salt marsh plant communities.
    Oecologia 05/2012; 170(3):789-98. DOI:10.1007/s00442-012-2356-2 · 3.09 Impact Factor
  • Brittany D McCall · Steven C Pennings ·
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    ABSTRACT: We examined geographic variation in the structure and function of salt marsh communities along the Atlantic and Gulf coasts of the United States. Focusing on the arthropod community in the dominant salt marsh plant Spartina alterniflora, we tested two hypotheses: first, that marsh community structure varies geographically, and second, that two aspects of marsh function (response to eutrophication and addition of dead plant material) also vary geographically. We worked at eleven sites on the Gulf Coast and eleven sites on the Atlantic Coast, dividing each coast up into two geographic areas. Abiotic conditions (tidal range, soil organic content, and water content, but not soil salinity), plant variables (Spartina nitrogen content, height, cover of dead plant material, but not live Spartina percent cover or light interception), and arthropod variables (proportional abundances of predators, sucking herbivores, stem-boring herbivores, parasitoids, and detritivores, but not total arthropod numbers) varied among the four geographic regions. Latitude and mean tidal range explained much of this geographic variation. Nutrient enrichment increased all arthropod functional groups in the community, consistent with previous experimental results, and had similar effects in all geographic regions, contrary to our hypothesis, suggesting widespread consistency in this aspect of ecosystem function. The addition of dead plant material had surprisingly little effect on the arthropod community. Our results caution against the uncritical extrapolation of work done in one geographic region to another, but indicate that some aspects of marsh function may operate in similar ways in different geographic regions, despite spatial variation in community structure.
    Oecologia 05/2012; 170(3):777-87. DOI:10.1007/s00442-012-2352-6 · 3.09 Impact Factor
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    Brittany D McCall · Steven C Pennings ·
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    ABSTRACT: Oil spills represent a major environmental threat to coastal wetlands, which provide a variety of critical ecosystem services to humanity. The U.S. Gulf of Mexico is a hub of oil and gas exploration activities that historically have impacted intertidal habitats such as salt marsh. Following the BP Deepwater Horizon oil spill, we sampled the terrestrial arthropod community and marine invertebrates found in stands of Spartina alterniflora, the most abundant plant in coastal salt marshes. Sampling occurred in 2010 as oil was washing ashore and a year later in 2011. In 2010, intertidal crabs and terrestrial arthropods (insects and spiders) were suppressed by oil exposure even in seemingly unaffected stands of plants; however, Littoraria snails were unaffected. One year later, crab and arthropods had largely recovered. Our work is the first attempt that we know of assessing vulnerability of the salt marsh arthropod community to oil exposure, and it suggests that arthropods are both quite vulnerable to oil exposure and quite resilient, able to recover from exposure within a year if host plants remain healthy.
    PLoS ONE 03/2012; 7(3):e32735. DOI:10.1371/journal.pone.0032735 · 3.23 Impact Factor

Publication Stats

4k Citations
362.95 Total Impact Points


  • 2002-2015
    • University of Houston
      • Department of Biology and Biochemistry
      Houston, Texas, United States
  • 2005
    • Stanford University
      Palo Alto, California, United States
  • 1999-2002
    • University of Georgia
      • Marine Institute at Sapelo
      Атина, Georgia, United States
  • 2001
    • University of Sunderland
      Sunderland, England, United Kingdom
  • 1991-2001
    • University of Guam
      Mangilao Village, Mangilao Municipality, Guam
  • 1990-2001
    • University of California, Santa Barbara
      • National Center for Ecological Analysis and Synthesis
      Santa Barbara, California, United States
  • 2000
    • Universität Ulm
      Ulm, Baden-Württemberg, Germany