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Nicholas J Kooyers, Benjamin K Blackman, Liza M Holeski
The latitudinal herbivory defense hypothesis (LHDH) postulates that the prevalence of species interactions, including herbivory, is greater at lower latitudes, leading to selection for increased levels of plant defense. While latitudinal defense clines may be caused by spatial variation in herbivore pressure, optimal defense theory predicts that clines could also be caused by ecogeographic variation in the cost of defense. For instance, allocation of resources to defense may not increase plant fitness when growing seasons are short and plants must reproduce quickly...
January 10, 2017: Ecology
Hao Ran Lai, Jefferson S Hall, Benjamin L Turner, Michiel van Breugel
Secondary forests are important carbon sinks, but their biomass dynamics vary markedly within and across landscapes. The biotic and abiotic drivers of this variation are still not well understood. We tested the effects of soil resource availability and competition by lianas on the biomass dynamics of young secondary tropical forests in Panama and assessed the extent to which liana effects were mediated by soil resource availability. Over a five year period, growth, mortality, and recruitment of woody plants of ≥1 cm diameter were monitored in 84 plots in 3-30 y-old secondary forests across the Agua Salud site in central Panama...
January 10, 2017: Ecology
Duncan N L Menge, Simon A Levin
Many tropical forests are characterized by large losses of plant-available forms of nitrogen (N), indicating that they are N-rich, and by an abundance of plants capable of symbiotic N fixation. These N-fixing plants can fix enough N to drive N-richness. However, biological N fixation (BNF) is more expensive than using plant-available N, so sustained BNF in N-rich soils appears to be a paradox. Here, we use spatially explicit ecosystem models to analyze the conditions under which spatial heterogeneity can induce simultaneous BNF and loss of plant-available N (hereafter, we call this combination "N-rich BNF")...
January 10, 2017: Ecology
Nicholas E Young, Ryan S Anderson, Stephen M Chignell, Anthony G Vorster, Rick Lawrence, Paul H Evangelista
Landsat data are increasingly used for ecological monitoring and research. These data often require preprocessing prior to analysis to account for sensor, solar, atmospheric, and topographic effects. However, ecologists using these data are faced with a literature containing inconsistent terminology, outdated methods, and a vast number of approaches with contradictory recommendations. These issues can, at best, make determining the correct preprocessing workflow a difficult and time-consuming task and, at worst, lead to erroneous results...
January 10, 2017: Ecology
Cassandra E Benkwitt
During major life-history transitions animals often experience high mortality rates due to predation, making predator avoidance particularly advantageous during these times. There is mixed evidence from a limited number of studies, however, regarding how predator presence influences settlement of coral-reef fishes and it is unknown how other potentially mediating factors, including predator origin (native versus non-native) or interactions among conspecific recruits, mediate the non-consumptive effects of predators on reef fish settlement...
January 10, 2017: Ecology
Tobias Züst, Anurag A Agrawal
The benefits of mutualistic interactions are often highly context dependent. We studied the interaction between the milkweed aphid Aphis asclepiadis and a tending ant, Formica podzolica. While this interaction is generally considered beneficial, variation in plant genotype may alter it from mutualistic to antagonistic. Here we link the shift in strength and relative benefit of the ant-aphid interaction to plant genotypic variation in the production of cardenolides, a class of toxic defensive chemicals. In a field experiment with highly variable genotypes of the common milkweed (Asclepias syriaca), we show that plant cardenolides, especially polar forms, are ingested and excreted by the aphid proportionally to plant concentrations without directly affecting aphid performance...
January 6, 2017: Ecology
Philip J Lester, Alexandra Sébastien, Andrew V Suarez, Rafael F Barbieri, Monica A M Gruber
Biological invasions are a threat to global biodiversity and provide unique opportunities to study ecological processes. Population bottlenecks are a common feature of biological invasions and the severity of these bottlenecks is likely to be compounded as an invasive species spreads from initial invasion sites to additional locations. Despite extensive work on the genetic consequences of bottlenecks, we know little about how they influence microbial communities of the invaders themselves. Due to serial bottlenecks, invasive species may lose microbial symbionts including pathogenic taxa (the enemy release hypothesis) and/or may accumulate natural enemies with increasing time after invasion (the pathogen accumulation and invasive decline hypothesis)...
December 31, 2016: Ecology
Tess Nahanni Grainger, Rachel M Germain, Natalie T Jones, Benjamin Gilbert
Theory describing the positive effects of patch size and connectivity on diversity in fragmented systems has stimulated a large body of empirical work, yet predicting when and how local species interactions mediate these responses remains challenging. We used insects that specialize on milkweed plants as a model metacommunity to investigate how local predation alters the effects of biogeographic constraints on species distributions. Species-specific dispersal ability and susceptibility to predation were used to predict when patch size and connectivity should shape species distributions, and when these should be modified by local predator densities...
December 30, 2016: Ecology
Philip A Martin, Adrian C Newton, James M Bullock
Invasive plants can alter ecosystem properties, leading to changes in the ecosystem services on which humans depend. However, generalizing about these effects is difficult because invasive plants represent a wide range of life forms, and invaded ecosystems differ in their plant communities and abiotic conditions. We hypothesize that differences in traits between the invader and native species can be used to predict impacts and so aid generalization. We further hypothesize that environmental conditions at invaded sites modify the effect of trait differences and so combine with traits to predict invasion impacts...
December 30, 2016: Ecology
Andrés G Rolhauser, Eduardo R Pucheta
How plant functional traits (e.g. seed mass) drive species abundance within communities remains an unsolved question. Borrowing concepts from natural selection theory, we propose that trait-abundance relationships can generally correspond to one of three modes of trait selection: directional (a rectilinear relationship, where species at one end of a trait axis are most abundant), stabilizing (an n-shaped relationship), and disruptive (a u-shaped relationship). Stabilizing selection (i.e. the functional convergence of abundant species) would result from positive density-dependent interactions (e...
December 30, 2016: Ecology
Lauren M Smith-Ramesh
Placing invasion in a more complete food-web context expands our understanding of species invasions to reflect the inherent complexity of ecological networks. Garlic mustard (Alliaria petiolata) has traditionally been predicted to dominate native communities through mechanisms embodied in popular hypotheses such as direct plant-plant interactions (allelopathy) and plant-herbivore interactions (enemy escape). However, garlic mustard also interacts directly with native predators by providing habitat for web-building spiders, which colonize the dry fruit structures (siliques) that garlic mustard leaves behind after it senesces...
December 30, 2016: Ecology
Krishna Pacifici, Brian J Reich, David A W Miller, Beth Gardner, Glenn Stauffer, Susheela Singh, Alexa McKerrow, Jaime A Collazo
The last decade has seen a dramatic increase in the use of species distribution models (SDMs) to characterize patterns of species' occurrence and abundance. Efforts to parameterize SDMs often create a tension between the quality and quantity of data available to fit models. Estimation methods that integrate both standardized and non-standardized data types offer a potential solution to the trade-off between data quality and quantity. Recently several authors have developed approaches for jointly modeling two sources of data (one of high quality and one of lesser quality)...
December 27, 2016: Ecology
Heather L Slinn, Matthew A Barbour, Kerri M Crawford, Mariano A Rodriguez-Cabal, Gregory M Crutsinger
Many host-plants exhibit genetic variation in resistance to pathogens; however, little is known about the extent to which genetic variation in pathogen resistance influences other members of the host-plant community, especially arthropods at higher trophic levels. We addressed this knowledge gap by using a common garden experiment to examine whether genotypes of Populus trichocarpa varied in resistance to a leaf-blistering pathogen, Taphrina sp., and in the density of web-building spiders, the dominant group of predatory arthropods...
December 27, 2016: Ecology
Elizabeth C Shaver, Andrew A Shantz, Ryan McMinds, Deron E Burkepile, Rebecca L Vega Thurber, Brian R Silliman
By inflicting damage to prey tissues, consumer species may increase stress in prey hosts and reduce overall fitness (i.e., primary effects, such as growth or reproduction) or cause secondary effects by affecting prey interactions with other species such as microbes. However, little is known about how abiotic conditions affect the outcomes of these biotic interactions. In coral reef communities, both nutrient enrichment and predation have been linked to reduced fitness and disease facilitation in corals, yet no study to date has tested their combined effects on corals or their associated microbial communities (i...
December 27, 2016: Ecology
Casey M Godwin, Emily A Whitaker, James B Cotner
The effects of resource stoichiometry and growth rate on the elemental composition of biomass have been examined in a wide variety of organisms, but the interaction among these effects is often overlooked. To determine how growth rate and resource imbalance affect bacterial carbon (C): nitrogen (N): phosphorus (P) stoichiometry and elemental content, we cultured two strains of aquatic heterotrophic bacteria in chemostats at a range of dilution rates and P supply levels (C:P of 100:1 to 10,000:1). When growing below 50% of their maximum growth rate, P availability and dilution rate had strong interactive effects on biomass C:N:P, elemental quotas, cell size, respiration rate, and growth efficiency...
December 19, 2016: Ecology
Winifred F Frick, Tina L Cheng, Kate E Langwig, Joseph R Hoyt, Amanda F Janicki, Katy L Parise, Jeffrey T Foster, A Marm Kilpatrick
Disease dynamics during pathogen invasion and establishment determine the impacts of disease on host populations and determine the mechanisms of host persistence. Temporal progression of prevalence and infection intensity illustrate whether tolerance, resistance, reduced transmission, or demographic compensation allow initially declining populations to persist. We measured infection dynamics of the fungal pathogen Pseudogymnoascus destructans that causes white-nose syndrome in bats by estimating pathogen prevalence and load in seven bat species at 167 hibernacula over a decade as the pathogen invaded, became established, and some host populations stabilized...
December 19, 2016: Ecology
Charlotte T Lee
Demographic analysis can elucidate how driving factors, such as climate or species interactions,affect populations. One important question is how growth would respond to future changes in the mean intensity of a driving factor or in its variability, such as might be expected in a fluctuating and shifting climate. Here I develop an approach to computing new stochastic elasticities to address this question. The linchpin of this novel approach is the multidimensional demographic difference that expresses how a population responds to change in the driving factor between two discrete levels of intensity...
December 19, 2016: Ecology
Maldwyn J Evans, Sam C Banks, Don A Driscoll, Andrew J Hicks, Brett A Melbourne, Kendi F Davies
Habitat loss and fragmentation are major threats to biodiversity and ecosystem processes. Our current understanding of the impacts of habitat loss and fragmentation is based largely on studies that focus on either short-term or long-term responses. Short-term responses are often used to predict long-term responses and make management decisions. The lack of studies comparing short- and long-term responses to fragmentation means we do not adequately understand when and how well short-term responses can be extrapolated to predict long-term responses, and when or why they cannot...
December 17, 2016: Ecology
Pamela Graff, Martin R Aguiar
A proposed refinement to the stress-gradient hypothesis (SGH) requires consideration of the strategies of the interacting species and the characteristics of the stress factors. While the strength and direction of these interactions can be predicted for different ecosystems, this idea remains largely untested in the field. We performed a manipulative field experiment complemented with a descriptive study to test the predictions in a natural setting that represents the extreme end of a precipitation gradient...
December 17, 2016: Ecology
Joy B Winbourne, Steven W Brewer, Benjamin Z Houlton
Limestone tropical forests represent a meaningful fraction of the land area in Central America (25%) and Southeast Asia (40%). These ecosystems are marked by high biological diversity, CO2 uptake capacity, and high pH soils, the latter making them fundamentally different from the majority of lowland tropical forest areas in the Amazon and Congo basins. Here, we examine the role of bedrock geology in determining biological nitrogen fixation (BNF) rates in volcanic (low pH) vs. limestone (high pH) tropical forests located in the Maya Mountains of Belize...
December 17, 2016: Ecology
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