Beach sand oil spills select for generalist microbial populations

The specialization-disturbance hypothesis predicts that, in the event of a disturbance, generalists are favored, while specialists are selected against. This hypothesis has not been rigorously tested in microbial systems and it remains unclear to what extent it could explain microbial community succession patterns following perturbations. Previous field observations of Pensacola Beach sands that were impacted by the Deepwater Horizon (DWH) oil spill provided evidence in support of the specialization-disturbance hypothesis. However, ecological drift as well as uncounted environmental fluctuations (e.g., storms) could not be ruled out as confounding factors driving these field results. In this study, the specialization-disturbance hypothesis was tested on beach sands, disturbed by DWH crude oil, ex situ in closed laboratory advective-flow chambers that mimic in situ conditions in saturated beach sediments. The chambers were inoculated with weathered DWH oil and unamended chambers served as controls. The time series of shotgun metagenomic and 16S rRNA gene amplicon sequence data from a two-month long incubation showed that functional diversity significantly increased while taxonomic diversity significantly declined, indicating a decrease in specialist taxa. Thus, results from this laboratory study corroborate field observations, providing verification that the specialization-disturbance hypothesis can explain microbial succession patterns in crude oil impacted beach sands.

Investigating Ecological Disturbance in Streams

Teaching students about ecological disturbance provides them with an understanding of a critical factor that shapes the structure and function of biological communities in environmental systems. This article describes four simple experiments and related curriculum that students can use to conduct inquiry around the theme of disturbance in stream ecosystems: insect drift, colonization, life history, and the intermediate disturbance hypothesis. Over five years, our students conducted these experiments 57 times; 79% of the experiments resulted in data that supported students’ hypotheses. Our findings show that the experiments can be used as a framework for inquiry-based learning about important ecological processes such as disturbance, dispersal, colonization, and succession. These experiments meet several of the Next Generation Science Standards, are easily and ethically conducted, and require very little equipment.

Predation Pressure on Sentinel Insect Prey along a Riverside Urbanization Gradient in Hungary

Urbanization is one of the most important global trends which causes habitat reduction and alteration which are, in turn, the main reasons for the well-documented reduction in structural and functional diversity in urbanized environments. In contrast, effects on ecological mechanisms are less known. Predation is one of the most important ecological functions because of its community-structuring effects. We studied six forest habitats along a riverside urbanization gradient in Szeged, a major city in southern Hungary, crossed by the river Tisza, to describe how extreme events (e.g., floods) as primary selective pressure act on adaptation in riparian habitats. We found a generally decreasing predation pressure from rural to urban habitats as predicted by the increasing disturbance hypothesis (higher predator abundances in rural than in urban habitats). The only predators that reacted differently to urbanization were ground active arthropods, where results conformed to the prediction of the intermediate disturbance hypothesis (higher abundance in moderately disturbed suburban habitats). We did not find any evidence that communities exposed to extreme flood events were preadapted to the effects of urbanization. The probable reason is that changes accompanied by urbanization are much faster than natural landscape change, so the communities cannot adapt to them.

Ground beetles (Coleoptera: Carabidae) react differently to urbanization than other predator groups in a riparian forest in southern Hungary

Urbanization is one of the most important processes shaping our environment, which causes habitat reduction and alteration which are, in turn, the main reasons for the reduced structural and functional diversity in urbanized environments. Predation is one of the most important ecological functions because of its community-structuring effects. Quantification of predation on invertebrate prey is difficult, because the attacks are mostly cryptic and it is rare when evidence is present. Using dummy prey, which is fixed to a surface, the marks left by predators allows us to identify them. Current evidence indicates that predation pressure is lower in urban than rural areas. According to the natural flow-regime paradigm, extreme events (e.g. floods) constitute a primary adaptive pressure in riparian habitats. We tested the validity of the paradigm in urbanized habitats. Our study site was in and around the city of Szeged (Hungary), along two urbanization gradients selected according to the Globenet protocol along the banks of the river Tisza and Maros. Data collection was conducted from April to October, 2014-2016. Both urbanization gradients included rural, suburban and urban areas, each characterised by an increase in the built up area (0%-25%-50%), intensity of forest management, and visitation rates by city residents. Overall 12672 dummy caterpillars ware placed, 6336 were on the ground level and 6336 on tree trunks. The dummy caterpillars (20 mm long, 3 mm thick) were made of light green plasticine, using a modified garlic press, fixed to the bark of trees or on a suitable surface on the ground with superglue, exposed for 24 h. The marks were identified using a hand-held magnifying glass (10 x). Overall the most active predator group was small mammals, followed by insects and birds. Urban predation activity on ground level, caused mainly by carabid beetles was significantly lower than the suburban or rural ones. Carabid predation pressure was higher in suburban than in rural habitats, while all other predator groups (other insects, birds and small mammals) had a decreasing trend towards urban habitats. This means, that all studied predator groups act according to the Gray’s increasing disturbance hypothesis, while carabid beetles react to urbanization according to Connell’s intermediate disturbance hypothesis. We found no evidence for the natural flow-regime paradigm along the examined urbanization gradients.