Microhabitat Utilization Research Articles

Competitive Interactions Between Benthic Stream Fishes, Riffle Sculpin, Cottus gulosus, and Speckled Dace, Rhinichthys osculus

Two morphologically dissimilar stream fishes occupied the same microhabitat in different riffles of Deer Creek, Tehama County, California. In a 12.5 km reach of the creek, speckled dace (Rhinichthys osculus) dominated riffles at the lower end while riffle sculpin (Cottus gulosus) dominated the riffles at the upper end, where dace were confined to slower water. Between these sets of riffles, relative abundances of the two species were negatively correlated. Routine metabolic rates of sculpin increased rapidly with temperature and indicated that sculpins were unable to tolerate temperatures in the low elevation riffles in the summer. Dace swimming performance appeared to be adequate at low temperatures to permit them to occupy the sculpin-dominated riffles. However, stream tank experiments indicated that at low temperatures sculpin were able to displace dace from cover in high velocity water. Our analysis thus demonstrated that competitive interactions between dace and sculpin for preferred microhabitat were mediated by temperature.Key words: competition, critical swimming velocity, experimental stream, microhabitat utilization, routine metabolism

Habitat Selection and Interspecific Competition in Two Species of Plethodontid Salamanders

A series of field enclosure and laboratory experiments was conducted to test the hypothesis that intespecific interference competition plays no role in the microhabitat utilization and activity patterns of the plethodontid salamanders Desmognathus fuscus and Desmognathus monticola. Single—species and mixed—species groups were tested to determine if the presence or absence of potential competitors influence either species' selection of substrate texture, selection of substrate moisture, utilization of cover object sizes, proximity to the stream bed, magnitude of activity and temporal activity patterns. In single—species groups significant differences were found between species in all of the variables tested except temporal activity pattern. Relative species differences in micro—habitat utilizations shown experimentally during this study reflect closely those commonly observed in the field for the two species. The preferences of each species for substrate texture, substrate moisture, and cover object sizes were independent of the presence or absence of potential competitors; temporal activity patterns were also independent of the composition of test groups. Evidence for interspecific interference was found, however, in the proximity of individuals to a stream bed, and in magnitude of activity. D. fuscus utilized microhabitats farther than from the stream bed and was significantly less active in the presence of D. monticola than when the latter species was absent. These two species of Desmognathus possess distinctly different patterns of hbatiat utilization and activity which could account for the field distributions observed; yet evidence for interspecific interference points to competition as another factor in their spatial distributions.

Guild Structure in Grasshopper Assemblages Based on Food and Microhabitat Resources

Guilds may be described as functional groupings of coexisting species which use resources in a very similar fashion. The presence of and specific membership in guilds are described for assemblages of grasshoppers (Orthoptera: Acrididae) from an arid grassland region of western Texas, USA. Two techniques were used to delineate the degree of guild structure in an assemblage of species based on both food and microhabitat utilization: (1) the method proposed by Inger and Colwell where the similarity of resource use with each nth nearest neighbor was used to delimit the degree of guild structure and, (2) an algorithm for grouping resource use by species was employed such that guilds were clusters of species which were separated from all other similar clusters by a distance which was greater than the largest distance between the two most disparate members of the guild in question. Results include the following: (1) much guild structure was observed in assemblages of grasshopper species for both diet and microhabitat. Each of the methods indicated similar (but not identical) patterns. (2) Similar patterns of guild structure were seen for assemblages from different sites which share only a portion of the same taxa of grasshopper (45% and 75% for two comparisons). (3) Guilds were not a result of random processes as was demonstrated by comparing actual resource utilization with randomized models. (4) Most species belonged to a guild based on either food (ca. 75%) or microhabitat (ca. 75%) use and sometimes both. (5) Hierarchical arrangements of species into guilds of increasing size were common.

Ecological organization of a Chihuahuan desert lizard community.

Niche relationships among 11 diurnal lizard species were studied for 3 years. The community appeared to be subdivided spatially into different subsets of only four to six species. Coexisting species of each subgroup were separated further by differential utilization of microhabitats. In late spring and early summer, when food shortage is likely, dietary overlaps between syntopic species were generally low but increased broadly after the rains, when food became plentiful. Because of the high similarity in prey-size utilization among large and medium species, effects of prey selection according to size were generally slight except for very different-sized species. Overlap in the three-dimensional resource space was high between Cnemidophorus scalaris and C. tigris, but close observation of the ecology of the two populations showed many small differences between them. We suggest that the very diversified ecological opportunism of C. scalaris allows it to coexist with C. tigris in a very heterogeneous ecosystem. Several hypotheses are discussed to explain the ecological determinism of resource partitioning within such a community.

Observaciones autoecológicas enLiolaemus nitidus(Lacertilia: Iguanidae)

Abstract In an attempt to provide background information that may lead to a more comprehensive understanding of the genus Liolaemus, the paper documents some basic features of the autecology of Liolaemus nitidus. The study was carried out at two typical localities where L. nitidus is found: at the coast north of Santiago de Chile, and at the Andes ranges east of Santiago. The following parameters were investigated: microhabitat utilization, preferred body temperatures, diet, weight of gonads and of fat bodies, and frequency of regenerated tails. The main findings reported are: Liolaemus nitidus is preferentially a rock‐dweller, although, when available, it can also be found perching on branches of the bromeliad Puya chilensis. Preferred field body temperatures, evaluated with a quick‐registering Schultheis thermometer, indicate that L. nitidus has a preferendum of about 35.4°C. This mean preferred body temperature is not statistically different from the laboratory preferendum reported in the literature. T...

Food and Microhabitat Utilization by Grasshoppers from Arid Grasslands: Comparisons with Neutral Models

Patterns of food and microhabitat use in arid grassland grasshopper communities are examined by comparing actual resource use with neutral models. A variety of neutral models is included in the analysis ranging from completely randomized resource utilization to models retaining much of the original community structure. Comparisons with resource utilization which are completely randomized indicate that biotic interactions are present for both diet and microhabitat niche dimensions. Average similarity in resource use of actual communities is much lower than in the analogous, completely randomized communities which suggests resource utilization by these species is hyperdispersed (on the average). However, mean niche overlap is not as low as possible which suggests other factors such as phylogenetic constraints on resource use or coevolved interactions which affect overall use of resources by a community are important.

Microhabitats of Woodland Centipedes in a Streamside Forest

Microhabitat utilization among several centipedes in a midwestern streamside forest was examined by pitfall-trapping and hand-collecting during 1973 and 1974. The woodland centipedes reported here include floodplain species (Lamyctes fulvicornis Meinert 1868) and 12 upland species. The upland centipedes can be further categorized as soil centipedes, log-limited centipedes [Sonibius politus (McNeill 1887) and Geophilus vitattus (Rafinesque 1826)], litter centipedes [(Scolopocryptops sexspinosa Say 1821), Pokabius bilabiatus (Wood 1867) and Strigamia bothriopa Wood 1862)] and log-litter species that occur in both microhabitats. No significant relationships were found between centipede abundance and any environmental factor, and no temporal patterns in microhabitat utilization were apparent.

Habitat Utilization, Competitive Interactions, and Coexistence of three Species of Cricetine Rodents in East‐Central Arizona

The ecological relationships of three cricetine species–Peromyscus maniculatus, Peromyscus boylii, and Neotoma stephensi–and their utilization of habitat were revealed by species removals from unfenced plots and vegetation tailoring experiments. When N. stephensi, a woodland and shrubland species of woodrat, was removed from a manzanita—oak shrubland and pinyon—juniper woodland, P. boylii showed few significant changes in its use of the vegetational microhabitats on the grid or in the nature of its arboreal activity. However, when P. boylii, a woodland and shrubland mouse, was removed from a grid in juniper—oak shrubland and juniper grassland, both P. maniculatus, an inhabitant of open habitats such as grassland, and N. stephensi expanded their microhabitat utilization and changed their patterns of aboveground activity. Subsequent removal of both N. stephensi and P. boylii from this plot resulted in further expansion of arboreal activity by P. maniculatus. After crown removal of 0.75 ha of manzanita—oak shrubland, P. boylii, but not N. stephensi, avoided the newly opened area. Habitat selection, differential resource utilization, and interspecific competition all contribute to the coexistence of these three species in patchy habitats.

Resource Allocation, Coexistence, and the Niche Structure of a Streambank Salamander Community

A streambank salamander community has proved to be an ideal system for investigating resource allocation and the evolution of community organization. Four aspects of microhabitat were investigated: substrate, substrate moisture, proximity to surface water, and size/type of cover utilized. Selection of substrate particle size was strongly positively correlated intra— and interspecifically (particularly the latter) with salamander body size, appearing to be a highly adaptive feature. The breadth or diversity of utilization of microhabitat components was interspecifically inversely related to body size. Definite shifts in microhabitat utilization and narrowing of niche (resource) breadths were observed in the presence of larger congeners. The mechanism of the shifts as well as the selective force that molded the organization of this community appear to be interspecific interference competition. Therefore, body sizes and species compositions in streambank salamander communities are determined by substrate size, its patchiness, and the presence of interference competitors. Observed macrohabitat distribution patterns have been analytically described and can be predicted by a knowledge of microhabitat preferences and niche breadths. The ratios of snout—vent lengths or head widths between adjacent species on a body size gradient for both adults and juveniles were remarkably constant, generally between 1.2 and 1.3. Mean prey size (width, length, and volume) also formed a geometric spacing which paralleled body sizes. The coefficient of variation (standard deviation/mean) was constant within a given measure of prey size. Morphological ratios for sympatric competitors in the range of 1.2 to 1.3 have been interpreted by investigators as character displacement to allocate prey sizes and therefore minimize competition. Such interpretations must be made carefully because in this study observed body size differences primarily reflect microhabitat allocation (the principal niche dimension of this study) and only secondarily allocation of prey sizes. Also, species packing (d/w) along the prey size resource gradient is much greater than anticipated by the theoretical May—MacArthur model and is demonstrated to be high in a community of opportunistic generalist insectivores. Species packing also requires careful interpretation because in reality spacings and widths of utilization functions are not uniform and separation of community members along a single niche dimension is rarely if ever encountered. Total niche overlap among community members (species and age classes) can accurately be determined because the relationships among the four microhabitat resources and the prey size dimension are known. The use of prey taxa as a niche dimension for opportunistic generalistic insectivores either overestimates or underestimates total niche overlap, since the utilization of prey items is a function of their size, the microhabitat preference of the predator, and stochastic events of prey occurrences. The community appears to be well coadapted since the following have been demonstrated: (1) total niche overlap is low, therefore minimizing competitive interactions, (2) interspecific predation could not be documented and must be minimal, and (3) demographic strategies are consistent in all macrohabitats regardless of congeneric composition.

Microhabitat Utilization and Species Distribution of Sympatric Small Mammals in Southwestern Ontario

To examine predictable patterns of small mammal species distribution several habitat measures were taken, and small mammal species recorded, in six major habitat types in southwestern Ontario. Peromyscus leucopus, P. maniculatus, Microtus pennsylvanicus, Tamias striatus, Zapus hudsonius and Blarina brevicauda were captured in large enough numbers for multivariate analysis. All species pairs except Blarina-Zapus were found to be significantly different in habitat utilization due to a combination of tree basal area, amount of vegetation between 0.25 m and 1 m, number ot trees, depth of dead grasses, leaves and other debris on the soil surface, and proportion of trees with first branches between 2 m and 3 m. Individual species predictably selected significantly different microhabitats. Species density of small mammals in southwestern Ontario was significantly correlated with the depth of dead grasses, leaves and other debris on the soil surface, a probable indicator of runway suitability and available productivity. Mean foliage height diversity was correlated with species density, whereas most measures of horizontal habitat heterogeneity were not good predictors of species number.

The Use of Space by Wintering Sparrows

Differences in microhabitat utilization by sparrows wintering in southeastern Arizona, USA may be sufficient to explain their coexistence. The species either forage in different mac- rohabitats or in the same habitat at different distances from tree or shrub cover. Seed size partitioning within habitats is sufficient to explain coexistence only in one case where the seed size distribution is bimodal. The species that forage in plains grassland habitat differ by foraging in concentric rings about tree or shrub cover. The behavior of each of these species appears to enhance predator avoidance and these behaviors change in a regular pattern with distance to cover both within and between species. Species foraging close to cover are social and tend to be conspicuous both in behavior and morphol- ogy. Two different strategies adapt species to avoiding predators at great distances to cover. In dense grassland, with increasing distance to shrub or tree cover, species in the genus Ammodramus are increasingly solitary and cryptic. In sparse grassland, Chestnut-collared Longspurs are social and cryptic on the ground but conspicuous in flight.

Seasonal Distribution and Abundance of Fishes in the Littoral Zone of a Michigan Lake

The seasonal distributions and abundances of 15 littoral zone fish species were determined from May to October 1976 in a small Michigan lake. A team of divers performed seven censuses along a set of transects which encompassed nearly the entire littoral region of the lake; additional dives enabled us to determine vertical distributions and migration patterns to and from overwintering areas. All species appeared to show less habitat segregation in spring when temperatures rose and food was abundant. Species distributions and abundances were quite constant during the summer and considerable habitat segregation was apparent. The bluegill (Lepomis macrochirus) was the dominant species and was studied in greater detail. Small bluegills (<80 mm total length) were confined throughout the year to the vegetation apparently to avoid predation; larger fish moved up in the water column. This species overwintered in two localized regions of tall perennial vegetation in the deep littoral apparently in response to predation and food availability. As the water warmed to 20 C the aggregations dispersed around the entire lake; this movement was reversed in autumn. These abundances and distribution patterns appear to be stable from year to year. This is probably due to the largely perennial vegetation structure and dependable resources in this marl lake. Temperature appears to set the overall bounds to the movements and habitats utilized, but ecological interactions are probably responsible for the finer resolution of microhabitat utilization among size classes and species in the littoral zone.

Ecology of Conus on eastern Indian Ocean fringing reefs: Diversity of species and resource utilization

The most diverse assemblages of the genus Conus known occur on fringing coral reefs in Thailand and Indonesia. As many as 27 congeneric species of these gastropods inhabit a single reef; in all, we examined 1,350 individuals of 48 species. Several attributes of the populations we observed conform to expectations of a model of ecological characteristics of bench and reef Conus proposed by Kohn (1971a). Number of species (S) averaged 15, and species diversity (H″) averaged 2.3 in the most heterogeneous habitat type — topographically complex, subtidal reef platforms (Type III habitat). Both species richness and evenness of distribution of individuals among species contribute strongly to H″. Fewer congeners and greater numerical dominance by single species characterize more homogeneous habitats. On subtidal reef platforms with large areas of sand substrate and less coral limestone (Type I–III habitat), mean values were S=10, and H″=1.6. In the one intensively studied, truncated reef-limestone platform (Type II–III intermediate habitat), S=13 and H″=1.4. Summed population density of all Conus species in Type III and I–III habitats is similar (0.02 to 0.05 individuals /m2) and comparable to estimates from similar habitats elsewhere in the Indo-West Pacific region. Mean density (0.7/m2) and other population attributes in Type II–III habitat more closely resemble those of Type II than Type III habitats in general. We combined analysis of species diversity and other attributes of assemblages in habitats of different environmental complexity with analysis of microhabitat and food-resource utilization, in order to demonstrate the extent to which specialization on different resources occurs in assemblages differing in diversity and habitat type. In the habitats studied, co-occurring species of Conus specialized to a greater extent on different prey species than on different microhabitat patches, but degree of microhabitat specialization was greater than in similarly complex habitats with assemblages of lower diversity elsewhere in the Indo-West Pacific region. While most Conus species preyed primarily on a different species or higher taxon of polychaetes, diets are not more specialized or dissimilar than in similar habitats elsewhere. Degree of specialization on different prey is not correlated with Conus species diversity in the different types of habitats studied. The data lead to the conclusion that differential predation is as important — and differential microhabitat utilization is more important — in permitting coexistence of potentially competing congeners, compared with conditions in habitats of comparable heterogeneity that support fewer congeners farther from the center of the Indo-West Pacific region. Pairwise comparisons of congeners indicate that many species pairs have low or no overlap in both microhabitat and food utilization. Members of species pairs with high overlap in microhabitat utilization typically eat different prey organisms, and those with similar diets typically occupy different habitats or microhabitats. This applies to molluscivorous as well as vermivorous species. Information on the diets of 11 species is reported here for the first time. Of 48 Indo-West Pacific Conus species whose food is now known, 35 prey on polychaetes, 2 on enteropneusts, 6 on gastropods, and 5 on fishes. Vermivorous Conus prey on relatively few of the polychaete species present in the environments. Species eaten represent only 12% of a total estimated polychaete population density of 27,000 individuals /m2. Certain very abundant polychaetes may be protected from predation by Conus by their small size, others by their long tubes. Two new aspects of size-selective predation by Conus are reported: (1) Although comparisons of predation rate with prey standing-crop suggest that food is plentiful, selective predation on the largest prey individuals present suggests that only small proportions of prey-species populations may have large enough body size to repay foraging effort by the Conus present; (2) composition of the diet changes qualitatively with increase in body size in several vermivorous Conus species; shifting by larger individuals to larger prey species could be documented in C. ebraeus.