Structure and resilience of the social network in an insect colony as a function of colony size

Social interactions are critical to the organization of worker activities in insect colonies and their consequent ecological success. The structure of this interaction network is therefore crucial to our understanding of colony organization and functioning. In this paper, I study the properties of the interaction network in the colonies of the social wasp Ropalidia marginata. I find that the network is characterized by a uniform connectivity among individuals with increasing heterogeneity as colonies become larger. Important network parameters are found to be correlated with colony size and I investigate how this is reflected in the organization of work in colonies of different sizes. Finally, I test the resilience of these interaction networks by experimental removal of individuals from the colony and discuss the structural properties of the network that are related to resilience in a social network. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau, and R. James).     

Use of Standardized Visual Assessments of Riparian and Stream Condition to Manage Riparian Bird Habitat in Eastern Oregon

The importance of riparian vegetation to support stream function and provide riparian bird habitat in semiarid landscapes suggests that standardized assessment tools that include vegetation criteria to evaluate stream health could also be used to assess habitat conditions for riparian-dependent birds. We first evaluated the ability of two visual assessments of woody vegetation in the riparian zone (corridor width and height) to describe variation in the obligate riparian bird ensemble along 19 streams in eastern Oregon. Overall species richness and the abundances of three species all correlated significantly with both, but width was more important than height. We then examined the utility of the riparian zone criteria in three standardized and commonly used rapid visual riparian assessment protocols—the USDI BLM Proper Functioning Condition (PFC) assessment, the USDA NRCS Stream Visual Assessment Protocol (SVAP), and the U.S. EPA Habitat Assessment Field Data Sheet (HAFDS)—to assess potential riparian bird habitat. Based on the degree of correlation of bird species richness with assessment ratings, we found that PFC does not assess obligate riparian bird habitat condition, SVAP provides a coarse estimate, and HAFDS provides the best assessment. We recommend quantitative measures of woody vegetation for all assessments and that all protocols incorporate woody vegetation height. Given that rapid assessments may be the only source of information for thousands of kilometers of streams in the western United States, incorporating simple vegetation measurements is a critical step in evaluating the status of riparian bird habitat and provides a tool for tracking changes in vegetation condition resulting from management decisions.     

USE OF DYE TRACERS TO COLLECT HYDROLOGIC DATA IN OREGON1

Dye tracers have been used in Oregon in the Collection of hydrologic data on 2,350 miles of stream channels in the Long Tom, Umpqua, Willmette, and John Day River basins, and in the Carmen-Smith power tunnel. These investigations demonstrated the usefulness, of dye tracers for determining: (1) estimates of traveltimes and travel rates of water, (2) discharge where standard methods of measuring are not applicable, and (3) dispersion characteristics of streams. Illustrations are used to present the results of time-of-travel studies in simple, concise, and readily interpreted form.     

Management concerns for swimming,tubing, and wading in the Great Smoky Mountains National Park

Recreational use of streams in the Great Smoky Mountains National Park has increased remarkably during recent years. To better manage the stream resource for visitor needs and at the same time preserve it for future generations, a user study was initiated in 1978. Use patterns, both spatial and temporal, and possible accompanying ecological impacts at three streams were investigated. Sampling was conducted at several sites per stream. The findings indicated that use was concentrated during afternoons and at certain streams and study sites. In addition, different types of users partitioned the streams according to stream morphology (form or structure of pools, riffles, etc.). Major impacts observed were soil compaction and erosion along the streambanks and physical disturbance of the stream bottoms by moving and placing stones to construct dams and raceways.     

Landscape-scale spatial population dynamics in human-impacted stream systems

The movement of individuals among populations can be critical in preventing local and landscape-scale species extinctions in systems exposed to human perturbation. Current understanding of spatial population dynamics in streams is largely limited to the reach scale and is therefore inadequate to address species response to spatially extensive perturbation. Using model simulations, I examined species response to perturbation in a drainage composed of multiple, hierarchically arranged stream-patches connected by in-stream and overland pathways of dispersal. Patch extinction probability, the proportion of initially occupied patches extinct after 25 years, was highly sensitive to the extent of species occupancy and perturbation within the drainage, longitudinal species distribution, perturbation decay rate and the covariance pattern of stochastic effects on colonization and extinction probabilities. Results of these simulations underscore the importance of identifying and preserving source populations and dispersal routes for stream species in human-impacted landscapes. They also highlight the vulnerability of headwater specialist taxa to anthropogenic perturbation, and the strong positive effect on species resilience of habitat rehabilitation when recolonization is possible. Efforts to conserve and manage stream species may be greatly improved by accounting for landscape-scale spatial population dynamics.     

Interaction Between Scientists and Nonscientists in Community-Based Watershed Management: Emergence of the Concept of Stream Naturalization

The authors' personal experience in watershed planning and decision making in the agricultural Midwest is described to illustrate how: (1) formalization of the process of community-based management is not sufficient to guarantee that local people will meaningfully consider scientific information and opinion when making decisions about watersheds, and (2) genuine social interaction between scientists and nonscientists requires a considerable investment of time and energy on the part of the scientist to develop personal relationships with nonscientists based on trust and mutual exchange of information. This experience provides the basis for developing a general conceptual model of the interaction between scientists and nonscientists in community-based watershed management in the agricultural Midwest. An important aspect of integrating science effectively into community-based decision making is the need to revise existing concepts to accommodate place-based contexts. Stream naturalization is introduced as an alternative to stream restoration and rehabilitation, which are viewed as inappropriate management strategies in human-dominated environments. Stream naturalization seeks to establish sustainable, morphologically and hydraulically varied, yet dynamically stable fluvial systems that are capable of supporting healthy, biologically diverse aquatic ecosystems. This general goal is consistent with the types of stream-management practices emerging from community-based decision making in human-dominated, agricultural landscapes. Further research on the linkages between geomorphological and ecological dynamics of human-modified agricultural streams over multiple spatial and temporal scales is needed to provide a sound scientific framework for stream naturalization.     

Dissolved oxygen sag analysis for a settling fields overlapping type multi-wastewater-outfall

The classical Streeter–Phelps models for Dissolved oxygen (DO) sag do not account for a significantly settleable portion (about 10% in treated to about 60% in the untreated wastewater discharged) of the total biochemical oxygen demand (BOD) inputs into rivers through wastewater outfalls, and therefore, they can not be used to predict the DO sag to any accuracy and rationality. The author’s rationally composited model for an accurate prediction of stream BOD, accounting for near linear removal of settleable BOD as well as simultaneous exponential decay of the non-settleable BOD, is used to predict the DO sag resulting from a multi-wastewater-outfall system, wherein the settling fields of some of the outfalls interfere and overlap. An illustrative case example has been presented to demonstrate use of the models evolved under varying locations of the multi-wastewater-outfalls. A universal and integrated PC based computer program can also be evolved for the computation of the overall resultant DO sag to confirm the manually computed DO sag.     

Gully control: Determining treatment priorities for gullies in a network

This report is about a newly developed procedure for setting priorities in gully control. It explains basic gully systems and developments as influenced by geomorphologic processes on which the proposed procedure is based. These processes consist of two types: one, representing interactions between the individual gullies of a network; the other, mechanisms initiated within a given gully by localized instability conditions. Classifying gullies into continuous and discontinuous types not only allows determination of network types but also points to critical locations that must be considered by the designer.The procedure for analyzing gully networks to establish treatment priorities consists of five steps as follows: 1) determining type of network based on gully types; 2) stream ordering of the network gullies; 3) tallying tributaries of each gully; 4) analyzing stage of development of each gully; 5) ranking of treatment priorities.Situations may exist—remote location and negligent downstream effects—where gully control is not desirable and the land manager decides to let nature take its course and to await the establishment of a new stream equilibrium condition before the watershed resources will be intensively utilized. Also political or funding aspects may not permit gully control efforts. Such aspects as well as types of individual treatment measures are beyond the scope of this report. The proposed technique establishes priorities that depend on opportunities to exert greatest control for least cost and to prevent the greatest amount of future erosion.     

A Rapid Method to Score Stream Reaches Based on the Overall Performance of Their Main Ecological Functions

A method was developed to score the ecological condition of first- to third-order stream reaches in the Auckland region of New Zealand based on the performance of their key ecological functions. Such a method is required by consultants and resource managers to quantify the reduction in ecological condition of a modified stream reach relative to its unmodified state. This is a fundamental precursor for the determination of fair environmental compensation for achieving no-net-loss in overall stream ecological value. Field testing and subsequent use of the method indicated that it provides a useful measure of ecological condition related to the performance of stream ecological functions. It is relatively simple to apply compared to a full ecological study, is quick to use, and allows identification of the degree of impairment of each of the key ecological functions. The scoring system was designed so that future improvements in the measurement of stream functions can be incorporated into it. Although the methodology was specifically designed for Auckland streams, the principles can be readily adapted to other regions and stream types.     

A morphological comparison of narrow,low-gradient streams traversing wetland environments to alluvial streams

Twelve morphological features from research on alluvial streams are compared in four narrow, low-gradient wetland streams located in different geographic regions (Connecticut, Indiana, and Wisconsin, USA). All four reaches differed in morphological characteristics in five of the features compared (consistent bend width, bend cross-sectional shape, riffle width compared to pool width, greatest width directly downstream of riffles, and thalweg location), while three reaches differed in two comparisons (mean radius of curvature to width ratio and axial wavelength to width ratio). The remaining five features compared had at least one reach where different characteristics existed. This indicates the possibility of varying morphology for streams traversing wetland areas further supporting the concept that the unique qualities of wetland environments might also influence the controls on fluvial dynamics and the development of streams. If certain morphological features found in streams traversing wetland areas differ from current fluvial principles, then these varying features should be incorporated into future wetland stream design and creation projects. The results warrant further research on other streams traversing wetlands to determine if streams in these environments contain unique morphology and further investigation of the impact of low-energy fluvial processes on morphological development. Possible explanations for the morphology deviations in the study streams and some suggestions for stream design in wetland areas based upon the results and field observations are also presented.