Jane C. Marks

Bio: Jane C. Marks is an academic researcher from Northern Arizona University. The author has contributed to research in topics: Plant litter & Ecosystem. The author has an hindex of 32, co-authored 85 publications receiving 3877 citations. Previous affiliations of Jane C. Marks include Royal Victoria Infirmary & Bowling Green State University.

Habitat segregation among trophic morphs of the Cuatro Ciénegas cichlid (Herichthys minckleyi)

Abstract: Herichthys minckleyi is an endangered, trophically polymorphic cichlid endemic to the Cuatro Cienegas basin of Coahuila, Mexico. A molariform morph has stout pharyngeal teeth whereas a papilliform morph has numerous fine pharyngeal teeth. Individuals with intermediate pharyngeal dentition also exist, as does yet another morph, called piscivore. Previous studies indicated that morphs utilize different food sources, thus suggesting morph-specific spatial segregation, since food resource availability is spatially heterogeneous. We present data from an observational study of all morphs (but focusing on the three most common, normal-bodied ones – molariform, papilliform and intermediate) in a single spring pool, Poza Mojarral Oeste. We analyzed morph distribution in relation to habitat types, and document morph-specific differences in feeding behavior. Spatio-temporal habitat partitioning was also investigated. Habitat use by molariform, papilliform, and intermediate morphs was found to be non-random. Morphs differed in habitat use, albeit with considerable overlap. Strong segregation among morphs was not detected in any season or time of day, but habitat use patterns varied seasonally within each morph and were consistently different among morphs. All morphs behave basically as feeding generalists. This endangered species may prove more difficult to manage than other, non-polymorphic species. It is clearly important to manage not only for the maintenance of the species, but also for maintenance of its different morphs, which our study indicates may each require different mixes of habitat types. We thus hypothesize that any changes in habitat heterogeneity will lead to altered proportions of the different morphs of the species.

Decreased growth of wild soil microbes after 15 years of transplant-induced warming in a montane meadow.

Abstract: The carbon stored in soil exceeds that of plant biomass and atmospheric carbon and its stability can impact global climate. Growth of decomposer microorganisms mediates both the accrual and loss of soil carbon. Growth is sensitive to temperature and given the vast biological diversity of soil microorganisms, the response of decomposer growth rates to warming may be strongly idiosyncratic, varying among taxa, making ecosystem predictions difficult. Here, we show that 15 years of warming by transplanting plant-soil mesocosms down in elevation, strongly reduced the growth rates of soil microorganisms, measured in the field using undisturbed soil. The magnitude of the response to warming varied among microbial taxa. However, the direction of the response-reduced growth-was universal and warming explained twofold more variation than did the sum of taxonomic identity and its interaction with warming. For this ecosystem, most of the growth responses to warming could be explained without taxon-specific information, suggesting that in some cases microbial responses measured in aggregate may be adequate for climate modeling. Long-term experimental warming also reduced soil carbon content, likely a consequence of a warming-induced increase in decomposition, as warming-induced changes in plant productivity were negligible. The loss of soil carbon and decreased microbial biomass with warming may explain the reduced growth of the microbial community, more than the direct effects of temperature on growth. These findings show that direct and indirect effects of long-term warming can reduce growth rates of soil microbes, which may have important feedbacks to global warming.

Variation in foraging behavior facilitates resource partitioning in a polymorphic cichlid, Herichthys minckleyi

Abstract: We examined foraging behavior (microhabitat use and feeding behavior) in a trophically polymorphic cichlid fish, Herichthys minckleyi, to address several questions regarding resource partitioning in this threatened species. These include: (1) do morphotypes demonstrate different foraging behaviors? (2) do individuals within a morphotype vary in their foraging behavior (e.g. are some individuals specialists, only using a subset of available resources, while other are generalists)? (3) do foraging behaviors vary between isolated pools? (4) do foraging behaviors vary across seasons? We quantified microhabitat use and feeding behavior for over 100 individuals (of two morphotypes) feeding freely in two isolated pools (populations) and across two seasons (winter and summer). We found differences in foraging behavior between morphotypes and individual specializations within morphotypes; i.e. some individuals specialize on certain food resources by using a few feeding behaviors within a subset of microhabitats, whereas others employ a range feeding behaviors across many microhabitats. Foraging behavior also varied between pools and across seasons. This spatial and temporal variation in foraging behavior and resource use may serve to maintain this polymorphism, as the relative fitness of the each morph may vary over space and time.

Effects of travertine and flow on leaf retention in Fossil Creek, Arizona

Abstract: Leaf retention is important in transferring energy from riparian trees to stream food webs. Retention increases with geomorphic complexity such as substrate coarseness, sinuosity, and the presence of debris dams. High discharge can reduce retention, particularly when streams lack physical trapping features. Travertine formations, caused by calcium carbonate deposition, can alter stream morphology. To date, however, we know of no study testing the effect of travertine on leaf retention. This study capitalized on a river restoration project in Fossil Creek, Arizona, where water was returned to the channel after a century of diversion. We examined how the fixed factors Flow (before and after restoration) and Morphology (travertine and riffle-pool sites) affected leaf retention. Leaf retention was higher in sites where travertine forms barriers across the river, relative to sites with riffle-pool morphology. Most leaves retained in travertine reaches were concentrated at the bottom of pools formed between dams. Although flow restoration did not alter retention rates across all sites, it diminished them at travertine sites, indicating an interaction between stream flow and morphology. We conclude that stream complexity and leaf retention are enhanced by travertine deposition but that high discharge can reduce the retentive capacity of in-stream structures.

Within-species variation in foliar chemistry influences aquatic leaf litter decomposition

Abstract: Leaf-litter inputs provide substrate and energy to stream systems. These contributions vary based on species-specific differences in litter quality, but little is known about how differences in litter quality within a species can affect ecosystem processes. Genetic variation within tree species, such as oaks and cottonwoods, affects ecosystem processes including decomposition and nutrient cycling in forest ecosystems and has the potential to do the same in streams. We collected litter from 5 genotypes of each of 4 different cottonwood cross types (Populus fremontii, Populus angustifolia, and natural F1 and backcross hybrids), grown in a common garden, and measured their decomposition rates using litter bags in the Weber River, Utah. The proportion of 35 species-specific P. fremontii restriction-fragment length polymorphism markers in the genotype explained 46% and genetically controlled phytochemical mechanisms (e.g., % soluble condensed tannin in litter) explained .72% of the variation in leaf-litter decomposition rate, respectively. Understanding how natural genetic variation in plants can affect ecosystem processes will provide baseline information with which to address the loss of genetic variation (through habitat fragmentation and global change) and altered genetic variation through hybridization with cultivars and transgenic manipulations in the wild.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Biofilms: an emergent form of bacterial life.

Abstract: Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Going back to the roots: the microbial ecology of the rhizosphere.

Abstract: The rhizosphere is the interface between plant roots and soil where interactions among a myriad of microorganisms and invertebrates affect biogeochemical cycling, plant growth and tolerance to biotic and abiotic stress. The rhizosphere is intriguingly complex and dynamic, and understanding its ecology and evolution is key to enhancing plant productivity and ecosystem functioning. Novel insights into key factors and evolutionary processes shaping the rhizosphere microbiome will greatly benefit from integrating reductionist and systems-based approaches in both agricultural and natural ecosystems. Here, we discuss recent developments in rhizosphere research in relation to assessing the contribution of the micro- and macroflora to sustainable agriculture, nature conservation, the development of bio-energy crops and the mitigation of climate change.