Shifts In Microhabitat Use Research Articles

Long‐term patterns of microhabitat use by fish in a southern Appalachian stream from 1983 to 1992: effects of hydrologic period, season and fish length

Abstract— We quantified microhabitat use by members of a southern Appalachian stream fish assemblage over a ten‐year period that included both floods and droughts. Our study site (37 m in length) encompassed riffle, run and pool habitats. Previous research indicated that species belonged to either benthic or water‐column microhabitat guilds. Most species exhibited non‐random microhabitat use in all seasons, and benthic and water column species generally were over‐represented in the deeper portions of the site. In addition, water column species generally were over‐represented in microhabitats with lower average velocities. The majority of seasonal shifts in microhabitat use were passive (i. e. correlated with changes in microhabitat availability), whereas, most shifts associated with hydrological periods appeared to be active responses to changing environmental conditions. Most species exhibited length‐related shifts in microhabitat use, which were strongly affected by hydrologic period for four of ten species. Microhabitat use patterns of assemblage members appeared to be a consequence of species‐specific responses to changing environmental conditions. The highly flexible patterns of microhabitat use exhibited by these species necessitate that decisions regarding their management be based on data covering a range of environmental conditions.

Effects of Introduced Bullfrogs and Smallmouth Bass on Microhabitat Use, Growth, and Survival of Native Red‐Legged Frogs (Rana aurora)

We examined the direct and indirect effects of two introduced species, the bullfrog (Rana catesbeiana) and smallmouth bass (Micropterus dolomieui), on the microhabitat use, growth, development, and survival of larval and metamorphic red‐legged frogs (Rana aurora). In field enclosure experiments, tadpoles ofR. auroraaltered their microhabitat use in the presence of both species. The shift in microhabitat use byR. auroracorresponded to increased activity in adultR. catesbeiana. Time to metamorphosis increased and mass at metamorphosis decreased whenR. auroratadpoles were exposed to either larval or adultR. catesbeiana. In contrast, smallmouth bass alone had little effect on the growth and development ofR. aurora. In all experiments, survivorship ofR. aurorawas significantly affected only whenR. aurorawere exposed to the combined effects of bullfrog larvae and adults or bullfrog larvae and smallmouth bass. Thus, the interaction between stages (larval‐adult) or species (bullfrog–smallmouth bass) produced indirect effects that were greater than when each factor was considered separately. Efectos de la Introducción de la Rana toroRana catesbeianay el PezMicropterus dolomieuien el Uso del Microhabitat, Crecimiento y Supervivencia de la Rana patirojaRana aurora Examinamos los efectos directos e indirectos de dos especies introducidas; la rana toroRana catesbeianay el pezMicropterus dolomieuien el uso del microhabitat, crecimiento, desarrollo y supervivencia de la Rana patirojaRana auroraen estados larvales y metamórficos. En encierros experimentales de campo, los renacuajos deR. auroraalteraron el uso de su microhábitat en presencia de ambas especies. El cambio en uso de microhábitat porR. auroracorrespondió con un incremento en la actividad de adultos deR. catesbeiana. El tiempo de metamorfósis incrementó y la masa durante metamorfósis disminuyó cuando los renacuajos deR. aurorafueron expuestos tanto a larvas como adultos deR. catesbeiana. En contraste, la presencia de soloMicropterus dolomieuituvo poco efecto en el crecimiento y desarrollo deR. aurora. En todos los experimentos la supervivencia deR. aurorafue significativamente afectada solo cuandoR. auroraestuvo expuesta a los efectos combinados de larvas y adultos de la rana toro y el pez. Por lo tanto, la interacción entre estados (larval/adulto) o especies (rana toro/Micropterus) produjo efectos indirectos que fueron mayores que cuando cada factor se consideró por separado.

Shifts in Microhabitat Use by the Lizard Psammodromus algirus: Responses to Seasonal Changes in Vegetation Structure

Environmental seasonality can be a major factor shaping activity, reproduction, foraging tactics, and habitat use of lizards (Fleming and Hooker, 1975; James and Shine, 1985; Lister and Garcia Aguayo, 1992). Animals living in variable environments may have sharply reduced reproductive fitness when the quality of the habitat is low (Ferguson et al., 1980; Patterson, 1991). To reduce these costs, individuals should be phenotypically plastic to cope with environmental changes, or they should leave unfavorable sites and search for better habitat.

COMMUNITY STRUCTURE OF SHORTGRASS-PRAIRIE RODENTS: COMPETITION OR RISK OF INTRAGUILD PREDATION?

Local assemblages of rodents in northern shortgrass prairie may reflect either predatory or competitive effects of northern grasshopper mice (Onychomys leucogaster) on other species such as deer mice (Peromyscus maniculatus). In an effort to distinguish these two types of effects, during the summer of 1994 I compared abundances, patterns of microhabitat use, and diets of P. maniculatus on four areas of shrub-dominated prairie in north-central Colorado to these characteristics on four similar sites where 0. leucogaster was removed. The abundance of P. maniculatus decreased during the study on both control and removal sites, but the decline was greater on controls, where numbers of 0. leucogaster increased. Declines in the abundance of P. maniculatus on individual study plots were correlated with abundances and recolonization rates of 0. leucogaster. Only 6% of P. maniculatus present on controls during pre-removal trapping were captured 7 wk later, compared to 32% of those initially present on removal sites. Furthermore, changes in the number of P. maniculatus were inversely related to the amount of shrub cover on sites, suggesting that shrubs may have provided refuge from 0. leucogaster, which rarely uses these microhabitats. Analyses of microhabitat use support this assertion; individual P. maniculatus increased their use of shrubs on control sites when 0. leucogaster was abundant, but there were no shifts in microhabitat use on removal sites. The proportions of arthropods in the diets of the two species were similar prior to Onychomys removals, and although P. maniculatus consumed fewer arthropods as the experiment progressed, diets did not differ between control and removal sites. In addition, Ord's kangaroo rats (Dipodomys ordii) increased slightly in number following removals, and western harvest mice (Reithrodon- tomys megalotis) colonized two removal sites. These results suggest that predatory or aggressive interference by 0. leucogaster, rather than exploitative competition, was re- sponsible for the observed changes in abundance and microhabitat use. Risk of aggression or predatory interference therefore may influence the local abundance and distribution of P. maniculatus and other small rodents on areas of shortgrass prairie where habitat char- acteristics permit coexistence.

Effects of Intraguild Interactions on Fitness and Microhabitat Use of Larval Ambystoma Salamanders

Two sympatric salamander species, Ambystoma jeffersonianum and A. maculatum, were evaluated to determine the relative effects of intraguild interactions. High larval densities increased mortality, and both species negatively affected the survivorship of each other. However, interspecific interactions did not differ significantly from the effects of intraspecific competition. Larval growth and survival were negatively correlated with the duration of water in the pond, and both species had similar mortality rates during two years of contrasting environmental extremes. Both species exhibited similar microhabitat usage when alone. When refugia were absent, both species suffered heavy mortality. Shifts in microhabitat use when refugia were present resulted in increased survivorship of larvae. Behaviors resulting in habitat partitioning and the use of refugia by larvae may be important components for the coexistence of A. maculatum and A. jeffersonianum in breeding ponds. These results indicate that A. maculatum is a more behaviorally variable species which is hypothesized to be a factor in the success of this widespread and common species.

Stability of Microhabitat Use by Brook Trout and Juvenile Atlantic Salmon after Stream Acidification

Microhabitat use by brook trout Salvelinus fontinalis and juvenile Atlantic salmon Salmo salar in a small acidic brook was examined in response to the acidification episodes typical of rivers of southwest Nova Scotia in the fall, and to a longitudinal pH gradient related to liming. Several microhabitat variables were measured for age-0 and age-1 and older fish of both species. Some of the measurements were made relative to the fishˈs focal point (height of the fish above the bottom) and included water depth and focal elevation, focal water velocity, focal water pH and temperature, and bed material grain size. The presence of a small, longitudinal pH gradient (<1 pH unit) along the brook did not alter microhabitat use by brook trout or juvenile Atlantic salmon, either in summer at pH greater than 5.5 or in the fall at pH less than 5.0. Similarly, a major acidification episode in the fall (>1 pH unit; final pH, <4.8) did not cause any major shift in microhabitat use by either species between summer and fall. The use of a particular microhabitat by fish generally reflected its availability, but some preferences in water depth and focal water velocity by age-0 fish ensured that Atlantic salmon and brook trout were effectively segregated at all times.

Do Rock Bass (Ambloplites rupestris) Induce Microhabitat Shifts in Mottled Sculpin (Cottus bairdi)?

In Coweeta Creek, North Carolina, mottled sculpin (Cottus bairdi) co-occurred seasonally with a potential predator, rock bass (Ambloplites rupestris). We conducted experiments to determine whether rock bass affected microhabitat use by sculpin in an artificial stream. The general behavior and microhabitat use of both species in the artificial stream resembled those observed in Coweeta Creek. When all microhabitat observations were pooled, there was little evidence of predator-induced shifts by sculpin. However, at night in trials without predators, sculpin generally occurred farther from shelter, over greater amounts of gravel and lower quantities of erosional substrata. When we added predators, however, this response was obviated. Nonetheless, the lack of strong responses by sculpin to rock bass, coupled with their co-occurrence only during seasons of low metabolic activity, lead us to suspect that rock bass do not produce strong shifts in microhabitat use by most sculpin in the Coweeta drainage.

Microhabitat use by fish in the upper Rio Matarraña, Spain, 1984–1987

Abstract– We evaluated the microhabitat use and abundance of Barbus graellsii, Bardus haasi, Chondrostoma toxostoma, Noemacheilus barbatulus, Oncorhynchus mykiss and Rutilus arcasii between 1984 and 1987 in the upper Rio Matarraña, Spain. The mean abundance classes for all species ranged from 1.8 to 3.0 (where 1=1–6, 2=6–10, 3=11–20 and 4=&gt;20 specimens, respectively). Mean abundance was consistently higher in 1984–1985 (2.4–3.0) than during 1986–1987 (1.8–2.8). The decreases noted in 1986–1987 were attributable to declines in abundance of O. mykiss (introduced in winter 1984) and B. haasi. Barbus graellsii and Ch. toxostoma, however, remained abundant throughout the entire 4‐year study. We only observed N. barbatulus and R. arcasii irregularly in the study site. Analyses of microhabitat availability data indicated that the study site contained more silt and less algae/debris during spring 1985 and early and late summer 1986 than in the majority of the remaining season. The converse was true for late summer 1985 (i. e., less silt and more algae/debris than the majority of seasons). Principal component analyses showed that B. graellsii and Ch. toxostoma generally occupied deeper microhabitats with low to average velocities, higher amounts of depositional substrata and lower quantities of erosional substrata. B. haasi tended to avoid microhabitats with rubble substrata and occurred in those with higher amounts of algae/debris. O. mykiss occupied shallower areas with slightly higher velocities and a heterogeneous substratum. With the exception of B. haasi, microhabitat use by assemblage members was similar from 1984 to 1987. B. haasi, however, was not as strongly affected by depth in the latter two years of the study as it was during 1984–1985. Seasonal and annual analyses of intraspecific microhabitat use showed that most changes were due to variations in microhabitat availability. Nonetheless, all species exhibited minor seasonal shifts in microhabitat use. Size‐related analyses indicated that both smaller B. graellsii and Ch. toxostoma occupied shallower microhabitats with slower velocities than larger specimens. Intersite differences in microhabitat use for B. graellsii and Ch. toxostoma showed that most differences in substratum use were attributable to disparities in substratum availability. Both species occurred closer to the substratum in the site with higher velocities (i. e., upper reach), although this response was more pronounced in Ch. toxostoma. Interspecific analyses indicated that B. graellsii and Ch. toxostoma did not consistently occupy statistically differentiable microhabitats, although both species occurred farther from the substratum and refuges than did B. haasi. O. mykiss occupied shallower microhabitats with more gravel than either B. graellsii or Ch. toxostoma. The lack of microhabitat shifts by native species during the study period indicates that interactions with either B. haasi or O. mykiss did not play a strong role in microhabitat use by the remaining assemblage members.

Influence of elevation on the thermoregulation of two sympatric lizards

Abstract The effect of elevation on thermoregulation strategy of the skink, Leiolopisma maccanni, and the gecko, Hoplodactylus maculatus, was studied during late summer, in Otago, New Zealand, where the two species are sympatric. Air temperature, operative temperature, and basking behaviour were studied at two sites of different elevation with similar mean air temperatures. At the higher elevation (1100 m), L. maccanni used microhabitats with lower operative temperatures, and increased their use of non‐basking microhabitat, when compared with skinks at the lower elevation site (200 m). Lower operative temperature and use of non‐basking habitat suggest that a physiological adjustment was observed in L. maccanni at higher elevations. H. maculatus did not display any shifts in microhabitat use, nor were there any significant differences in thermoregulation between the two elevations. Nocturnal activity and thigmothermy restrict H. maculatus to a thermal conforming strategy.

Application of a cluster-bootstrapping method for identifying the dietary patterns of fish populations

Dietary data usually exhibit considerable statistical awkwardness and the analytical techniques commonly used in the study of fish diet suffer from various problems (especially at the intraspecific and intrapopulation levels) resulting from difficulties in group definition and pooling of data. Considering that, we advocate the use of a combination of cluster analysis and bootstrapping to identify statistically significant groups of individual predators. Both basic and extended versions of the procedure (yielding slightly different results) are outlined. We also suggest the use of detrended correspondence analysis (DCA) for further interpretation of significant clusters. When applied to dietary data from a brown trout population, the method successfully finds different feeding patterns, even though possible sources (geographical and temporal) of dietary variation were very limited. Dietary patterns appear to be related to the seasonal dynamics of the prey community coupled with seasonal shifts in microhabitat use by the predator; and, in a finer time-scale, to diel macroinvertebrate drift periodicity or interindividual, size-related differences in preyhandling capabilities.

Seasonal Changes in Microhabitat Selection by Rainbow Trout in a Small Stream

Abstract Shifts in microhabitat selection by rainbow trout Oncorhynchus mykiss were related to seasonal and ontogenetic factors in a small stream characterized by short riffles, small pools, and boulder substrate. Resource availability did not differ significantly between summer and November sampling dates for most variables related to water velocity, substrate, and cover, although depths were greater and temperatures were significantly lower in November. Ontogenetic shifts were found for total depth, focal elevation, mean water column velocity, focal velocity, surface velocity, and substrate, but not for relative depth or temperature. When microhabitat selection was adjusted for fish size, selection was significantly different between seasons, most notably for velocity. Ontogenetic shifts in microhabitat use by young-of-year rainbow trout were interrupted by cooling winter temperatures. These changes resulted in substantially different microhabitat requirements for all rainbow trout size-classes in diffe...

Population Responses of Surfperch Released from Competition

Previous short—term (behavioral) field experiments revealed that two temperate marine reef fish, black surfperch (Embiotoca jacksoni) and striped surfperch (E. lateralis), compete with one another along a depth gradient. Here we report abundance responses of these viviparous species following 4 yr of sustained release from competition with each other. We tested predictions derived from the short—term experiments concerning the symmetry of interspecific competitive effects on abundance. We also explored among—habitat variation in the occurrence and magnitude of density compensation. Populations of both surfperch species increased on the order of 40% at experimental (competitor—removal) sites; no change in density was detected for either species at unmanipulated control sites. These strong, reciprocal effects on density conformed with our expectations based on behavioral shifts in microhabitat use immediately following competitive release and on correlation analyses between population densities and feeding—associated resources, but not with predictions from habitat shifts (e.g., changes in depth distribution) that occurred shortly after manipulation. Density compensation was detected only in habitats (depths) where behavioral responses to competitive release had occurred (i.e., in shallow reef habitats). The correlation analyses accurately predicted variation in the relative magnitude of density compensation among habitats and among populations; predictions of the absolute changes in density based on the analyses were less accurate. Take together, these results suggest that behavioral experiments may be useful in identifying potential spatial variability in competitive effects on density. “Scaling—up” the results of behavioral experiments to project relative interspecific effects on density will be more problematic, in part because the relative demographic costs of the interaction may not be accurately portrayed.

Influence of Behavioral Thermoregulation on Microhabitat Use by Two Sceloporus Lizards

I investigated the relationship between microhabitat use and behavioral thermoregulation in the lizards Sceloporus occidentalis and S. graciosus. I studied two populations of each species along a 1300—m elevational gradient in the San Gabriel Mountains of southern California. These species occupy different, but overlapping, elevational ranges, with S. graciosus occurring at higher elevations. Because their ranges differ, the species experience different thermal environments; however, they are nearly identical in several measures of thermal physiology. Body temperatures of active lizards varied little with altitude, although air temperatures decrease substantially over this range. Both species compensated behaviorally for variation in thermal environments by varying basking frequency and microhabitat use. By thermoregulating, lizards maintained body temperatures that favor high levels of locomotor performance and other physiological functions. Microhabitat use varied markedly with elevation. Sceloporus occidentalis was almost completely arboreal at low elevation; lizards of both species were partly arboreal, partly terrestrial at intermediate elevation; and S. graciosus was mainly terrestrial at high elevations. Thus, the species converged in microhabitat use where sympatric. These shifts in microhabitat use paralleled altitudinal changes in (i) the spatial location of thermally suitable microhabitats and (ii) habitat structure. Behavioral thermoregulation, then, appears to be an important determinant of habitat use in these lizards. Results of this study may have important implications for lizard community ecology. Microhabitats that are otherwise appropriate for lizards can be thermally unsuitable depending on the local thermal environment. Hence, the thermal environment and lizard thermal biology constrain patterns of structural habitat use. As a result, physiological considerations could limit the behavioral and evolutionary options for species experiencing interspecific competition. For example, competitors in sympatry may be unable to evolve microhabitat resource partitioning because only a subset of microhabitats are thermally suitable.

Ontogenetic and Seasonal Shifts in Microhabitat Use by the Lizard Cnemidophorus sexlineatus

I studied the microhabitat use patterns of adult and juvenile six-lined racerunners, Cnemidophorus sexlineatus, through thermally distinct seasons in southern Oklahoma from 1982-84. Principal components analysis indicated that juveniles used more exposed microhabitats than adults during most of the year. This was probably due to size-related differences in the biophysical properties of lizards that result in large lizards being at greater risk of overheating in exposed microhabitats. Adult racerunners show non-random microhabitat use during the mild seasons whereas juveniles show non-random microhabitat use during the hottest season. The exposure and thermal qualities of the spectrum of microhabitats potentially available to lizards changes seasonally. Both age classes show a parallel seasonal shift in microhabitat use with respect to thermal habitat parameters but are invariant with respect to exposure. This suggests microhabitat exposure is a more important cue for lizard microhabitat selection than thermal parameters.

Spatial organization of a desert rodent community: food addition and species removal.

From 1977 through 1983 we conducted experiments on a desert rodent community where supplemental seeds were added or certain rodent species and ants were removed from 0.25-ha fenced plots in a Chihuahuan Desert site in southeastern Arizona, USA. In this paper we examine the patterns of microhabitat use relative to vegetative cover by 11 rodent species. The results show that: i) removal of the largest seed-eating species, Dipodomys spectabilis, produced the most pervasive and dramatic shifts in microhabitat use by the remaining rodent species; ii) adding seeds or removing ants had little effect on the spatial use of microhabitats by rodents in this community; and iii) non-granivores were just as likely as granivores to shift microhabitat use when other granivores were removed. We believe these results indicate that both food and foraging microsites are limited but the relegation of subdominant species to lesspreferred microhabitats by the large Dipodomys spectabilis is the major factor underlying the spatial organization of this community. Results also demonstrate that strong interactions among species increase the probability that pathways of indirect interactions through intermediary species are important; these complex linkages may include species that overlap little in food preferences.

Microhabitat Use by an Assemblage of California Stream Fishes: Developing Criteria for Instream Flow Determinations

Microhabitat requirements were determined for eight species of native California stream fishes: Rainbow trout Salmo gairdneri; Sacramento sucker Catostomus occidentalis; Sacramento squawfish Ptychocheilus grandis; hardhead Mylopharodon conocephalus; California roach Hesperoleucus symmetricus; speckled dace Rhinichthys osculus; tule perch Hysterocarpus traski; and riffle sculpin Cottus gulosus. Two or three size classes were evaluated for each species. Each species had a preferred microhabitat (defined on the basis of depth, velocity, substrate), as did each size class within each species, but there was much similarity in microhabitat use within and among species. The amount of microhabitat available to each species differed in three stream reaches in which availability was quantified, but the differences were not enough to explain the differences in composition of the fish assemblage found at each site. This study indicates that recommendations for instream flows should be based on microhabitat use data collected on site together with habitat availability data. Even on-site data should be used cautiously because intraspecific interactions and changes in a streamˈs physical characteristics, especially in its temperature regime, may cause unexpected shifts in microhabitat use.