Showing papers by "Jane C. Marks published in 2006"

A framework for community and ecosystem genetics: from genes to ecosystems

Abstract: Can heritable traits in a single species affect an entire ecosystem? Recent studies show that such traits in a common tree have predictable effects on community structure and ecosystem processes. Because these 'community and ecosystem phenotypes' have a genetic basis and are heritable, we can begin to apply the principles of population and quantitative genetics to place the study of complex communities and ecosystems within an evolutionary framework. This framework could allow us to understand, for the first time, the genetic basis of ecosystem processes, and the effect of such phenomena as climate change and introduced transgenic organisms on entire communities.

Litter quality, stream characteristics and litter diversity influence decomposition rates and macroinvertebrates

Abstract: SUMMARY 1. We examined the relative importance of litter quality and stream characteristics in determining decomposition rate and the macroinvertebrate assemblage living on autumnshed leaves. 2. We compared the decomposition rates of five native riparian tree species (Populus fremontii, Alnus oblongifolia, Platanus wrightii, Fraxinus velutina and Quercus gambelii) across three south-western streams in the Verde River catchment (Arizona, U.S.A.). We also compared the decomposition of three- and five-species mixtures to that of single species to test whether plant species diversity affects rate. 3. Decomposition rate was affected by both litter quality and stream. However, litter quality accounted for most of the variation in decomposition rates. The relative importance of litter quality decreased through time, explaining 97% of the variation in the first week but only 45% by week 8. We also found that leaf mixtures decomposed more quickly than expected, when all the species included were highly labile or when the stream environment led to relatively fast decomposition. 4. In contrast to decomposition rate, differences in the invertebrate assemblage were more pronounced across streams than across leaf litter species within a stream. We also found significant differences between the invertebrate assemblage colonising leaf mixtures compared with that colonising pure species litter, indicating non-additive properties of litter diversity on stream invertebrates. 5. This study shows that leaf litter diversity has the capacity to affect in-stream decomposition rates and stream invertebrates, but that these effects depend on both litter quality and stream characteristics.

Plant genes link forests and streams.

Abstract: Although it is understood that the composition of riparian trees can affect stream function through leaf litter fall, the potential effects of genetic variation within species are less understood. Using a naturally hybridizing cottonwood system, we examined the hypothesis that genetic differences among two parental species (Populus fremontii and P. angustifolia) and two groups of their hybrids (F1 and backcrosses to P. angustifolia) would affect litter decomposition rates and the composition of the aquatic invertebrate community that colonizes leaves. Three major findings emerged: (1) parental and hybrid types differ in litter quality, (2) decomposition differs between two groups, a fast group (P. fremontii and F1 hybrid), and a slow group (P. angustifolia and backcross hybrids), and (3) aquatic invertebrate communities colonizing P. fremontii litter differed significantly in composition from all other cross types, even though P. fremontii and the F1 hybrid decomposed at similar rates. These findings are in agreement with terrestrial arthropod studies in the same cottonwood system. However, the effects are less pronounced aquatically than those observed in the adjacent terrestrial community, which supports a genetic diffusion hypothesis. Importantly, these findings argue that genetic interactions link terrestrial and aquatic communities and may have significant evolutionary and conservation implications.

Feeding specialization in Herichthys minckleyi: a trophically polymorphic fish

Abstract: Diet specialization in the trophically polymorphic cichlid fish Herichthys minckleyi was examined using gut contents. Individual H. minckleyi were categorized as having molariform, papilliform or undetermined pharyngeal jaws. The presence of enlarged flattened pharyngeal jaw teeth was used to categorize H. minckleyi as molariform, and the possession of only small pencil-like pharyngeal teeth was used to classify fish as papilliform. Undetermined individuals (<50 mm standard length, L S ) were not assigned to one of the two larger morphotypes. Arthropods were found to be generally rare in H. minckleyi gut contents, but when present, they were most frequently recovered from undetermined individuals. The percentage of plant material consumed by undetermined H. minckleyi was not as great as papilliforms ingested on average, and snail crushing by undetermined H. minckleyi was not evident. A significantly greater mean percentage of plant detritus was recovered from papilliforms compared to molariforms. Snails were crushed by molariforms more frequently than by papilliforms. When only molariforms and papilliforms that had crushed snails were compared, a greater number of snails were crushed by molariforms. No relationship was found between molariform L S and the number of snails crushed, but greater molariform tooth number, adjusted for Ls, was indicative of recent snail crushing. The maintenance of H. minckleyi pharyngeal jaw variation could be promoted by intraspecific diet differentiation.

Role of fish in structuring invertebrates on stromatolites in Cuatro Cienegas, Mexico

Abstract: Stromatolites, the dominant Precambrian life form, declined in the Phanerozoic to occur today in only a few sites. This decline has been attributed to evolution of metazoan grazers, but stromatolites in our study site, Cuatro Cienegas, Coahuila, Mexico, harbor diverse macroinvertebrates. Drawing on food chain theory, we hypothesized that fish predation on invertebrates controls invertebrate populations, allowing stromatolites to flourish in Cuatro Cienegas. Our experiment used small mesh (1 mm) cages to exclude all but larval fishes, and larger (6.5 mm) cages to exclude all larger fishes (including the molluscivorous and omnivorous endemic polymorphic cichlid, Herichthys minckleyi), but allow access to all sizes of the abundant endemic pupfish, Cyprinodon bifasciatus. No effects of treatments on invertebrate densities were noted at 6 week, but significant effects were observed on specific taxonomic groups after 3 month. In absence of fishes, hydrobiidae snails and ceratopogonids increased 3- and 5-fold, respectively, and invertebrate assemblage composition varied among treatments. Algal biomass was not affected by treatments, but algal species composition appeared to change. Overall results suggest that fish assemblages structure invertebrate assemblages, and that fishes may also be factors in determining algal communities.