Nancy E. McIntyre

Ecology of Urban Arthropods: A Review and a Call to Action

Abstract A review of the entomological literature revealed relatively few general studies on arthropods in urban environments, excluding those in the context of pest control or epidemiology, and all were limited in scope and duration. Most studies documented the presence and abundance of species in a variety of poorly quantified urban categories. There also were a number of studies on the effects of urban pollution and changes in arthropod community composition over time (particularly in urban green areas). From these studies, three groups of arthropods could be identified: (1) “rural” taxa not present (or at lower abundance) in urban settings, (2) “urban” taxa present only (or at higher abundance) in urban settings, and (3) taxa present in both rural and urban settings with no particular affinity for either. The lack of a basic understanding of the mechanisms accounting for distributional and abundance patterns of urban arthropods illustrates the many opportunities for entomological research that exist in urban settings. Some of these opportunities are outlined to encourage further work on the ecology of urban arthropods.

Ground arthropod community structure in a heterogeneous urban environment

Despite being conspicuous and influential features of the biosphere, urban ecosystems have been neglected in ecological research. Arthropods are abundant in urban settings, but little is known about how these animals respond to urbanization. We systematically monitored the structure of ground arthropod communities for 12 months at 16 sites representing the four most abundant forms of urban land use (residential, industrial, agricultural, and desert remnant) in a rapidly growing metropolitan area (Phoenix, AZ). Although taxonomic richness was comparable among land-use types, community composition differed, with certain taxa being uniquely associated with each form of land use. Three taxa (springtails, ants, and mites) were extremely widespread and abundant, accounting for over 92% of captures; when these three taxa were excluded from analysis, however, differences were revealed in arthropod community composition with urban land use. Trophic dynamics also varied with land use: predators, herbivores, and detritivores were most abundant in agricultural sites, while omnivores were equally abundant in all forms of land use. These community-level differences resulted from taxon-specific responses to habitat structure, which varied with land use. Because arthropod community structure is affected by habitat structure and land use, and because arthropods play key roles in nutrient cycling, organic matter decomposition, pollination, and soil aeration, the spatial heterogeneity of urban ecosystems therefore may affect ecosystem functioning.

Urban Ecology as an Interdisciplinary Field: Differences in the use of “Urban” Between the Social and Natural Sciences

Though there is a growing appreciation of the importance of research on urban ecosystems, the question of what constitutes an urban ecosystem remains. Although a human-dominated ecosystem is sometimes considered to be an accurate description of an urban ecosystem, describing an ecosystem as human-dominated does not adequately take into account the history of development, sphere of influence, and potential impacts required in order to understand the true nature of an urban ecosystem. While recognizing that no single definition of “urban” is possible or even necessary, we explore the importance of attaching an interdisciplinary, quantitative, and considered description of an urban ecosystem such that projects and findings are easier to compare, repeat, and build upon. Natural science research about urban ecosystems, particularly in the field of ecology, often includes only a tacit assumption about what urban means. Following the lead of a more developed social science literature on urban issues, we make suggestions towards a consistent, quantitative description of urban that would take into account the dynamic and heterogeneous physical and social characteristics of an urban ecosystem. We provide case studies that illustrate how social and natural scientists might collaborate in research where a more clearly understood definition of “urban” would be desirable.

Urbanization and warming of Phoenix (Arizona, USA): Impacts, feedbacks and mitigation

This paper examines the impacts, feedbacks, and mitigation of the urban heat island in Phoenix, Arizona (USA). At Sky Harbor Airport, urbanization has increased the nighttime minimum temperature by 5°C and the average daily temperatures by 3.1°C. Urban warming has increased the number of “misery hours per day” for humans, which may have important social consequences. Other impacts include (1) increased energy consumption for heating and cooling of buildings, (2) increased heat stress (but decreased cold stress) for plants, (3) reduced quality of cotton fiber and reduced dairy production on the urban fringe, and (4) a broadening of the seasonal thermal window for arthropods. Climate feedback loops associated with evapotranspiration, energy production and consumption associated with increased air conditioning demand, and land conversion are discussed. Urban planning and design policy could be redesigned to mitigate urban warming, and several cities in the region are incorporating concerns regarding urban warming into planning codes and practices. The issue is timely and important, because most of the worlds human population growth over the next 30 years will occur in cities in warm climates.

Linking Microbial Community Structure and Function to Seasonal Differences in Soil Moisture and Temperature in a Chihuahuan Desert Grassland

Global and regional climate models predict higher air temperature and less frequent, but larger precipitation events in arid regions within the next century. While many studies have addressed the impact of variable climate in arid ecosystems on plant growth and physiological responses, fewer studies have addressed soil microbial community responses to seasonal shifts in precipitation and temperature in arid ecosystems. This study examined the impact of a wet (2004), average (2005), and dry (2006) year on subsequent responses of soil microbial community structure, function, and linkages, as well as soil edaphic and nutrient characteristics in a mid-elevation desert grassland in the Chihuahuan Desert. Microbial community structure was classified as bacterial (Gram-negative, Gram-positive, and actinomycetes) and fungal (saprophytic fungi and arbuscular mycorrhiza) categories using (fatty acid methyl ester) techniques. Carbon substrate use and enzymic activity was used to characterize microbial community function annually and seasonally (summer and winter). The relationship between saprophytic fungal community structure and function remained consistent across season independent of the magnitude or frequency of precipitation within any given year. Carbon utilization by fungi in the cooler winter exceeded use in the warmer summer each year suggesting that soil temperature, rather than soil moisture, strongly influenced fungal carbon use and structure and function dynamics. The structure/function relationship for AM fungi and soil bacteria notably changed across season. Moreover, the abundance of Gram-positive bacteria was lower in the winter compared to Gram-negative bacteria. Bacterial carbon use, however, was highest in the summer and lower during the winter. Enzyme activities did not respond to either annual or seasonal differences in the magnitude or timing of precipitation. Specific structural components of the soil microbiota community became uncoupled from total microbial function during different seasons. This change in the microbial structure/function relationship suggests that different components of the soil microbial community may provide similar ecosystem function, but differ in response to seasonal temperature and precipitation. As soil microbes encounter increased soil temperatures and altered precipitation amounts and timing that are predicted for this region, the ability of the soil microbial community to maintain functional resilience across the year may be reduced in this Chihuahuan Desert ecosystem.

Effects of forest patch size on avian diversity

The effects of landscape patchiness on the diversity of birds of the Georgia Piedmont were investigated during 1993. Birds were sampled along line transects within relatively large (10–13.25 ha) and small (less than 3.25 ha) forest patches located within nonforest agricultural landscapes. Patterns of habitat use in these patches were compared to those in contiguous forest patches larger than 13.25 ha. Analysis of variance revealed significant differences in diversity between large and small woodlots and between contiguous and fragmented landscapes, especially in terms of the numbers of edge and interior species and winter-resident, summer-resident, and year-round birds observed.

HOW DOES HABITAT PATCH SIZE AFFECT ANIMAL MOVEMENT? AN EXPERIMENT WITH DARKLING BEETLES

We used an experimental model system consisting of darkling beetles (Coleoptera: Tenebrionidae, Eleodes obsoleta Say) in a microlandscape to assess the effects of habitat patch size on the movement patterns of animals. The ratio of habitat area to nonhabitat in a 25-m2 “microlandscape” was held constant while the grain of patchiness (patch size) was varied in four treatments. Beetle movement pathways were electronically surveyed, and seven pathway metrics were used to quantify movement characteristics. ANOVA and Fisher’s Protected Least Significant Difference post hoc comparisons revealed that both the presence and the grain of spatial heterogeneity influenced how animals moved through landscapes. Intermediate patch sizes elicited the strongest behavioral responses, whereas movements were similar between finely patchy landscapes with small habitat patches and coarsely patchy landscapes with larger habitat patches. These results indicate that organisms may use landscapes that possess different configurations of habitat in similar ways. Predicting how organisms respond to spatial heterogeneity therefore requires an assessment of how organisms use landscapes, in addition to an assessment of the structural characteristics of landscapes, such as grain size.

A comparison of live versus kill pitfall trapping techniques using various killing agents

We compared the efficacies of two arthropod pitfall trapping techniques: live (dry) trapping and kill trapping with three killing agents (water, ethylene glycol, and the recently developed propylene glycol, whose efficacy has not been previously assessed). Kill pitfall traps caught more species than did live pitfalls. Forty‐one species were collected only from kill traps (3 being unique to water, 11 to ethylene glycol, and 8 to propylene glycol), 12 were collected only from live traps, and 32 were collected from both kill and live traps. The same average number of individuals per species was caught for most of those taxa that were collected in both trap types, indicating that better retention of captured arthropods by the killing agent was not responsible for the differences observed in the two pitfall trapping methods. There were no significant differences in captures between propylene and ethylene glycol traps or between water and live traps. Because of species‐specific differences in the efficiencies of live and kill pitfall trapping, cross‐study entomological comparisons made using kill pitfall trapping and live pitfalling may be confounded.

A novel use of the lacunarity index to discern landscape function

Discerning the function of a landscape involves comparing landscape use with spatial patterns. To do this requires both quantification of landscape use and landscape pattern and a means of comparing the two. An index of lacunarity has been used to quantify spatial pattern (specifically, habitat contagion). We demonstrate a new way of using the lacunarity index to quantify landscape function as well. We calculated lacunarity to describe landscape patchiness of experimental landscapes with respect to patterns of habitat and non-habitat areas (the previous use of lacunarity) as well as to describe patterns of patch use by animals in those landscapes, irrespective of habitat-patch patterns (a novel application of lacunarity). We demonstrate a disparity between landscape pattern and landscape use. This finding suggests that drawing generalizations of, and making predictions about, how animals respond to landscape spatial structure may not be straightforward.

Completing the data life cycle: using information management in macrosystems ecology research

An important goal of macrosystems ecology (MSE) research is to advance understanding of ecological systems at both fine and broad temporal and spatial scales. Our premise in this paper is that MSE projects require integrated information management at their inception. Such efforts will lead to improved communication and sharing of knowledge among diverse project participants, better science outcomes, and more transparent and accessible (ie “open”) science. We encourage researchers to “complete the data life cycle” by publishing well-documented datasets, thereby facilitating re-use of the data to answer new and different questions from the ones conceived by those involved in the original projects. The practice of documenting and submitting datasets to data repositories that are publicly accessible ensures that research results and data are available to and use-able by other researchers, thus fostering open science. However, ecologists are often unfamiliar with the requirements and information management tools for effectively preserving data and receive little institutional or professional incentive to do so. Here, we provide recommendations for achieving these ends and give examples from current MSE projects to demonstrate why information management is critical for ensuring that scientific results can be reproduced and that data can be shared for future use.