The arrangement of resources in patchy landscapes: effects on distribution, survival, and resource acquisition of chironomids

Abstract

The spatial arrangement of resources in patchy habitats influences the distribution of individuals and their ability to acquire resources. We used Chironomus riparius, a ubiquitous aquatic insect that uses leaf particles as an important resource, to ask how the dispersion of resource patches influences the distribution and resource acquisition of mobile individuals in patchy landscapes. Two experiments were conducted in replicated laboratory landscapes (38×38 cm) created by arranging sand and leaf patches in a 5×5 grid so that the leaf patches were either aggregated or uniformly dispersed in the grid. One-day-old C. riparius larvae were introduced into the landscapes in one of three densities (low, medium, high). In experiment 1, we sampled larvae and pupae by coring each patch in each landscape 3, 6, 12, or 24 days after adding larvae. In experiment 2, emerging adults were collected daily for 42 days from each patch in each landscape. In aggregated landscapes, individuals were aggregated in one patch type or the other during a particular developmental stage, but the "preferred" type changed depending on developmental stage and initial density. Adult emergence was lower by about 30% in all aggregated landscapes. In dispersed landscapes, individuals used both types of patch throughout their life cycles at all initial densities. Thus, patch arrangement influences the distribution of mobile individuals in landscapes, and it influences resource acquisition even when average resource abundance is identical among landscapes. Regardless of patch arrangement, high initial density caused accumulation of early instars in edge patches, 75% mortality of early instars, a 25% increase in development time, and a 60% reduction in adult emergence. Because mortality was extremely high among early-instar larvae in high-density treatments, we do not have direct evidence that the mechanism by which patch arrangement operates is density dependent. However, the results of our experiments strongly suggest that dispersion of resource patches across a landscape reduces local densities by making non-resource patches available for use, thereby reducing intraspecific competition.

Habitat heterogeneity and disturbance influence patterns of community temporal variability in a small temperate stream

“…Habitat heterogeneity affects ecological processes at all levels of organization, including behavior (Holomuzki & Biggs, 1999;Kie et al, 2002), population dynamics (Silver et al, 2000), species interactions (Crowder & Cooper, 1982;Scognamillo et al, 2003), community structure (Hansen, 2000, Tews et al, 2004, and ecosystem functioning (Cardinale et al, 2002). Likewise, theoretical studies invoke habitat heterogeneity to explain a plethora of phenomena, including diversity (Pianka, 1966;Horner-Devine et al, 2004, but see Cramer & Willig, 2005 for an empirical counter-perspective), coexistence (Hutchinson, 1961;Holt, 1984), and variability in species interactions (Holt & Hassell, 1993).…”

Effects of elevated salinity from road deicers on Chironomus riparius at environmentally realistic springtime temperatures

“…Thus, larvae in the 0 g/L chambers were 1 to 2 d older at the beginning of the experiment than larvae in the other salinity treatments. However, larvae molt from 1 st to 2 nd instar in 2 to 3 d and remain in the 2 nd instar for ,1 wk (StankoMishic et al 1999, Silver et al 2000. Thus, all larvae should have been at approximately the same developmental stage during the temperature manipulations.…”

“…We added 100 larvae to each of 9 experimental culture chambers identical in construction to the culture chambers described above. We chose this density to prevent possible effects of overcrowding because C. riparius larvae exhibit density-dependent growth and development (Silver et al 2000, Hooper et al 2003. We did not have enough larvae to stock all chambers on 1 d, so we added them on successive days.…”

“…Chironomus riparius occurs in lakes and wetland habitats throughout North America and is salt tolerant (Bervoets et al 1996, Jonusaite et al 2011). Diapause in 3 rd -and 4 th -instar C. riparius can be induced by environmental stressors, such as overcrowding and food limitation (Silver et al 2000), decreased light, and cold temperatures (Goddeeris et al 2001), and can markedly prolong development time. Third-and 4 th -instar larvae overwinter in cocoons in the sediment in cold climates and may exhibit supercooling (the ability to lower the body temperature at which internal water freezes ;Lencioni 2004).…”

Predator density and dissolved oxygen affect body condition of Stenonema tripunctatum (Ephemeroptera, Heptageniidae) from intermittent streams

“…Condition values of odonates in some studies were lowest when intraspecific densities were high (Johnston et al, 1984;Pierce et al, 1985), but an experimental study (Baker, 1989) failed to detect an intraspecific density effect. Pool drying in intermittent streams caused insect densities to increase (Williams et al, 2003), which can possibly result in higher levels of intraspecific competition, especially when resources were aggregated (Silver et al, 2000). However, pool drying also caused fish densities to increase which can reduce size at emergence (Dahl & Peckarsky, 2002), or reduce aquatic insect densities (Williams et al, 2003) and relax intraspecific competition.…”