Habitat heterogeneity facilitates coexistence of two syntopic species of Peromyscus in a temperate forest of Central México

An essential topic in ecology is to understand how the structure of the habitat and its changes in space and time (i. e., habitat heterogeneity) affect the frequency and interactions between cohabiting species. Here, we assessed the effect of the biotic and abiotic components that configure the microhabitat heterogeneity and its temporal shifts (dry and rainy seasons), on the frequency (total and by sex) of two congeneric species, Peromyscus difficilis and P. melanotis, that co-occurs in a temperate forest of Central Mexico. To address this, an experimental plot composed of 120 sampling stations was placed within a temperate forest in the National Park Desierto de los Leones, Mexico City. In each sampling station, we set Sherman traps to capture mice of two syntopic Peromyscus, and we also evaluated six variables related to the spatial heterogeneity of the habitat during two rainy seasons. Our results revealed differential effects of habitat heterogeneity on the frequency of each species. Moreover, habitat heterogeneity also had a different effect on male and female frequencies of each Peromyscus species. While P. difficilis was captured more frequently in sampling stations with high presence and coverage of logs in the soil, P. melanotis was regularly captured in sampling stations with high vegetation cover and plant species richness. Thus, it seems that the different requirements and habitat preferences of these two Peromyscus species facilitate their spatial and temporal coexistence in this mid-latitude temperate forest. In general, we provide evidence of the importance of studying the heterogeneity of the habitat to better understand the interactions between syntopic species, offering new insights into the spatial and temporal mechanisms that could determine its coexistence at local scale.

Macrofaunal Diversity and Community Structure of the DeSoto Canyon and Adjacent Slope

Macrofauna within the DeSoto Canyon, northern Gulf of Mexico (GOM), along the canyon wall and axis, and on the adjacent slope, were sampled along with sediment, terrain, and water mass parameters. Within the canyon, abundance and species richness decreased with depth, while evenness increased. Cluster analysis identified three depth-related groups within the canyon that conformed to previously established bathymetric boundaries: stations at 464 – 485 m, 669 – 1834 m, and > 2000 m. Abundance differed between depth groups. Species richness was lowest for the deepest group and evenness was lowest for the shallowest. Community structure within the canyon most related to fluorometry and oxygen saturation, combined with any of salinity, particulate organic carbon, sediment organic carbon, or slope.Canyon wall abundances were higher than the canyon axis or adjacent slope. Community structure differed between all three habitat types. Ordination of community structure suggests a longitudinal pattern that potentially tracks with increasing sea-surface chlorophyll that occurs in the eastward direction across the northern GOM. Canyon and slope differences may result from seasonal water masses entrained by canyon topography characterized by high salinity, oxygen saturation, fluorometry, and turbidity. Higher fluorescence and turbidity in the canyon did not translate into higher sediment organic matter. Flushing along canyon wall channels and the canyon axis may explain the low organic matter. Differences in abundance and structure between the canyon wall and axis may result from microhabitat heterogeneity due to potential hydrocarbon seepage, organically enriched sediment deposits along channels, or remnant influence from the Deepwater Horizon blowout.

Beaver activity increases habitat complexity and spatial partitioning by steelhead trout

Freshwater habitat restoration is a major conservation objective, motivating efforts to restore habitat complexity and quality for fishes. Restoration based on the engineering activities of beavers (Castor canadensis) increases fish habitat complexity, but how this affects fish habitat use and movement behaviours is not well known. We used a network of passive integrated transponder antennas to quantify small-scale movement and microhabitat use of 175 individual juvenile steelhead (Oncorhynchus mykiss) in a stream channel with a complex bathymetric profile resulting from a beaver impoundment and in a simplified channel devoid of beaver activity. Our results show that juvenile steelhead exploit microhabitat heterogeneity by employing a range of behaviours that maximizes available habitat via spatial and temporal partitioning among individuals. These results suggest spatial resource partitioning as a potential mechanism for the previously established positive correlations among steelhead density, survival, and production with beaver-based restoration within the study watershed. More broadly, our findings provide insight as to how populations can exploit habitat complexity through spatial partitioning that can be informative for planning restoration and management actions.

Effects of human impacts on diversity and distribution of chironomids (Diptera: Chironomidae) in prealpine springs

Diversity and distribution of chironomid fauna (Diptera: Chironomidae) in 36 springs in the Italian Prealps (Veneto and Trentino NE-Italy, 46°N, 10-11°E) was studied in relation to altitude, spring type and grade of disturbance. The springs were located between 62 and 1710 m asl of altitude, in three calcareous mountain areas (Mt. Baldo, Mts. Lessini and Mt. Pasubio). They differed in conservation status (natural, moderately and highly disturbed) and belonged to five hydromorphological types (rheocrene, limnocrene, rheohelocrene, rheolimnocrene, rheohygropetric). Each spring was surveyed once, between early summer and autumn, within 50 m of the spring’s source (eucrenal). A total of 4198 chironomid larvae and pupae were sorted from 111 macroinvertebrate samples collected, belonging to five subfamilies (Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae), 41 genera and 60 species/groups of species, and three juveniles taxa. As expected, Orthocladiinae accounted for a large part of specimens (88%) and species (74%), with Tvetenia calvescens/bavarica as the most frequent and abundant taxon, shared by pristine and disturbed springs and by all spring types. Most taxa were found in few sites, and frequencies declined gradually for most wider distributed species. A high number (74%) of rare (= present in less than 10% of sites) taxa were found and from one to 23 taxa were identified per spring. Maximum richness occurred in moderately disturbed (Shannon-H = 1.29±0.60) springs, located at medium-high altitude (385-1266 m asl), according to the intermediate disturbance hypothesis. Even the evenness (Equitability-J) was higher as average in these springs. A Cluster Analysis run on Bray-Curtis similarity index highlighted a high similarity i) between the chironomid assemblages of moderately disturbed and natural springs (44 species in each spring group, with 29 species in common), and ii) between rheocrene and rheohelocrene types, thus the springs with the highest microhabitat heterogeneity. High individuality of springs was revealed, and new information about non-biting midges autecology provided. The utility of chironomids as bioindicators of water quality and ecological state of springs was confirmed, with some species e associated with high disturbance level (e.g., Polypedilum nubeculosum gr. to water intake works) and others with pristine conditions (e.g., Pseudodiamesa branickii).

Spatial and Temporal Changes in Habitat Heterogeneity Promote Partition of Resources of Small Mammals in a Midlatitude Temperate Forest

One of the basics and fundamentals problems in ecology is understand the factors that shape the spatial patterns in the distribution of the species and the coexistence of close relatives species. Among the most important factors governing the distributions and the coexistence of species are the spatiotemporal changes occurring in the microhabitat heterogeneity. Here, we assessed the heterogeneity of microhabitats and how they have an effect in the spatial segregation of two species of small mammals (i. e., Peromyscus difficilis and P. melanotis), which coexist in a temperate, mixed forest. We evaluated the microhabitat heterogeneity through multivariate statistics, using onto 23 habitat variables for vertical-horizontal habitat structure along pluvial seasons. To detect specific microdistribution changes and habitat preferences by two species of small mammals, we used second order spatial statistics and general linear models. According to their respective morphology and locomotive adaptations, the middle sized, midscansorial P. difficilis was resident all year long and preferred microhabitats with a high log ground cover, while the opportunistic, small sized, cursorial P. melanotis changed its occupancy area, depending on density of herbaceous and woody plants cover. Under the more benign microhabitat conditions of rainy season (denser plant coverage, milder temperature), both species showed closer microdistribution patterns; while these became repulsive at the less benign conditions of dry season (scarcer plant cover, colder temperature). Thus, we could confirm that seasonal changes of microhabitat heterogeneity promoted Peromyscus coexistence, through dispersion patterns reflecting partition of microhabitat resources.