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There is a longstanding interest in describing the factors determining food chain length in ecological communities. Likewise, there has been considerable interest in explaining why food chain lengths differ in terrestrial and aquatic systems. The ‘energetic efficiency hypothesis' predicts endothermy and body size should be negatively correlated with food chain length. Using a large database of published food webs, we assessed the relationships between food chain length, endothermy, body size, and food-web structure. We utilized 77 published food webs spanning marine, freshwater, and terrestrial systems, ranging in species richness from 8–224 taxa. As expected, mean food chain lengths (MFCLs) in aquatic systems were significantly longer than those of terrestrial systems, even when comparing food webs of similar size and species richness. Endotherms were more numerous and occurred lower in terrestrial food chains compared to aquatic ones. Endotherms were also consumed by fewer predators and fed on more resources than ectotherms in terrestrial systems. This partially explains the decrease in trophic structuring and food chain paths in these systems (which was negatively correlated with MFCLs). The fraction of endotherms at the herbivore level was a strong predictor of MFCL in terrestrial systems, whereas the average difference in body mass between herbivores and their resources was the best predictor of MFCL in aquatic systems. This suggests that both body size and endothermy at the herbivore level play an important role in determining food chain lengths.
Combining our knowledge of how wildlife species behave across space and time broadens our understanding of patterns of resource use. Temporal patterns of activity may be shaped by species morphology and physiology, major disturbances in an ecosystem, seasonal shifts in abundances of resources, or habitat preferences. Camera traps and univariate kernel density estimates can now be used to quantify temporal activity patterns throughout the day in wildlife. Our goals were to quantify how daily activity patterns of mammals common to southern New England differ between two focal habitat types [i.e., early successional (ES) and mature hardwood (MH) forest patches] and to quantify how temporal activity patterns change seasonally. For all species with sufficient observations, temporal activity patterns did not differ significantly between adjacent ES and MH habitat patches. Daily temporal activity was greatest in the fall and winter for cottontail (Sylvilagus spp.), but we did not detect shifts in activity among seasons in any other species. With sufficient data these methods could be expanded to address questions of how temporal activity patterns may change when compared across an interaction of seasons and habitats, as well as how patterns of temporal activity change in the context of the broader surrounding landscape.
The range and habitat affinities of the rock vole (Microtus chrotorrhinus, Rodentia, Muridae) have been enigmatic, especially at the western margin of its range, a problem made more difficult because the species is rare or uncommon throughout its range. We recorded rock voles at 53 new sites in northern Minnesota and observed broader habitat associations than the boulder fields and talus commonly reported. The distribution in Minnesota corresponds to the Vermilion ground moraine of the Rainy lobe of the Pleistocene late Wisconsinan glaciation, a striking association of a mammalian species range limit with a geological feature other than a local geosite.
Freshwater fish surveys were conducted at 178 lakes and streams at 13 islands in the Aleutian Archipelago and two islands in the Pribilof Islands during May-September 2002 and 2006-2010. Seven fish species were documented: coho salmon (Oncorhynchus kisutch), rainbow trout (O. mykiss), Dolly Varden (Salvelinus malma), anadromous, and resident freshwater threespine stickleback (Gasterosteus aculeatus species complex), ninespine stickleback (Pungitius pungitius), coastrange sculpin (Cottus aleuticus), and Alaska blackfish (Dallia pectoralis). Resident freshwater threespine stickleback and Dolly Varden were the most commonly trapped fish. Ninespine stickleback were found only in the Near Islands group. Populations of resident freshwater threespine stickleback containing a low frequency of individuals with two or four dorsal spines were collected in the Near Islands group and at Adak Island. Sympatric species pairs of anadromous and resident freshwater threespine stickleback were collected in the Andreanof Islands, Rat Islands, and Near Islands groups. Avian piscivores were more commonly observed at lakes with fish. This study provides baseline data for freshwater fish management within the Alaska Maritime National Wildlife Refuge.
The Peppered Chub Macrhybopsis tetranema was once found throughout the Arkansas River basin in portions of Texas, New Mexico, Oklahoma, Kansas, and Colorado. Range-wide declines in both abundance and distribution have occurred over the past three decades coinciding with habitat loss and fragmentation. Over the last decade or more, only two geographically isolated Peppered Chub populations persisted in the Arkansas and Ninnescah rivers in Kansas and a portion of the Canadian River in New Mexico and Texas. Intensive sampling between 2011 and 2013 documented the decline of this species from Kansas during consecutive years of region-wide drought in 2011 and 2012. Equally intensive sampling in 2015 in reaches of the Ninnescah and Arkansas rivers yielded no individuals, suggesting the potential extirpation of this population. Conversely, Peppered Chub were consistently collected in the Canadian River in New Mexico from 2012 to 2015 with increasing numbers in recent years with higher flows. Therefore, Peppered Chub is either extirpated or has declined below detection in Kansas and a stable population only remains in a 220 km reach of the Canadian River. A recovery plan for the Peppered Chub might consider restoration and maintenance of adequate seasonal fluctuating river flows, removal of barriers, and repatriation to river reaches that have experienced extirpation.
Although most owls exhibit biparental care, the relative contributions of males and females during critical life cycle stages are poorly understood. Further information could improve our understanding of the feeding ecology of owls and of mechanisms that govern natural and sexual selection, particularly as they relate to the evolution of reversed sexual dimorphism. The objective of our study was to assess possible intersexual differences in provisioning behavior (visit rate and prey size and type) of slightly dimorphic Eastern Screech-Owls (Megascops asio; females 17% greater mass than males) during the post-brooding period when both adults provision nestlings. Pairs of Eastern Screech-Owls provisioned young with 16 different types of prey in our study with insects and crayfish (Family Astacidae) being the most common. We found no differences between females and males in provisioning rate or in mean size of prey delivered. Our findings suggest Screech-Owls are opportunistic feeders in the post-brooding period and that food niche partitioning does not occur between the sexes. These findings are inconsistent with the Role Differentiation and Ecological Hypotheses made for the evolution of reversed sexual dimorphism but support the Rate Ingestion Hypothesis which predicts that both sexes may take smaller prey during the post-brooding period to increase ingestion rate and decrease handling time. In addition our results contribute to an understanding of the feeding ecology and life history of one of the most widespread and recognizable raptors in North America.
We recorded 19 visits by ferruginous hawks (Buteo regalis) over 6 d at two black–tailed prairie dog (Cynomys ludovicianus) subcolonies poisoned with the rodenticide Rozol® Prairie Dog Bait (0.005% chlorophacinone active ingredient) and at an adjacent untreated subcolony. Before Rozol® application ferruginous hawks foraged in the untreated and treated subcolonies but after Rozol® application predation by ferruginous hawks was only observed in the treated subcolonies. We suggest that ferruginous hawks' preference for hunting in the treated subcolonies after Rozol® application was influenced by the availability of easy-to-capture prey, presumably due to Rozol® poisoning. The energetically beneficial behavior of favoring substandard prey may increase raptor encounters with rodenticide exposed animals if prey vulnerability has resulted from poisoning.
Spatial resource distribution and phenology are critical factors for the development, emergence, and reproduction of solitary hymenopterans. However, the biotic and abiotic conditions that drive changes in their spatiotemporal distributions remain poorly understood. We surveyed the cavity-nesting hymenopteran community in a region of California oak-chaparral habitat over 3 y. Most taxa had short seasonal activity periods, with >90% of observations occurring within a single month for six of eight taxa studied. Predaceous wasps including Euodynerus foraminatus and Trypoxylon tridentatum were most abundant during the warmer mid-season months, while megachilid bees showed divergent phenologies consistent with temporal niche separation by species. Similarly, while some taxa were abundant and widespread across the study site, most showed relatively restricted spatial distributions. Spatial distributions were only partially explained by the dominant vegetation type; although some taxa showed significant preferences for oak- or chamise-dominated habitats, in most cases, differences in nesting abundance were not statistically significant. Parasitism rates ranged from zero to 57% among reared host taxa, with the relatively generalist Monodontomerus spp. as the most common parasitoids observed. These observations describe a community with strong within-population phenological synchrony, variation in species distribution patterns, and species composition influenced by spatial habitat heterogeneity.
Decomposition of allochthonous organic matter that enters shaded headwater streams during a short autumn leaf fall period provides much of the energy the streams receive throughout the year. As such, alterations of riparian communities, including those resulting from invasive species, should have a significant impact on these energy inputs and potentially alter microbial communities and the behavior of shredders that process leaf litter. We compared consumption of leaves of an abundant native species (green ash Fraxinus pennsylvanica) and nonnative species (common buckthorn Rhamnus cathartica) by the northern spring amphipod Gammarus pseudolimnaeus, with and without periods of stream conditioning. Amphipods consumed a very small proportion of the unconditioned leaves of common buckthorn and green ash and demonstrated no significant preference for the unconditioned leaves of either species. When leaves were stream-conditioned, there was a significant interaction between the effects of leaf species and days of stream conditioning on both the mass and area of leaf disks consumed by the amphipods. Overall there was a greater consumption of buckthorn leaves compared to ash, with peak consumption occurring during a narrower range of conditioning times for buckthorn. Common buckthorn's higher overall consumption level is expected to provide rapid and short-lived input of energy into the stream, in marked contrast to the slower and more sustained input from native green ash. These results suggest there may be significant changes in the organic matter dynamics of stream ecosystems throughout the Midwest as common buckthorn continues its expansion and green ash declines with the invasion of emerald ash borers (Agrilus planipennis).
Midwestern oak savanna systems are typically defined by their open canopy and the co-existence of scattered mature oak trees and a ground layer dominated by herbaceous vegetation. The structure of these systems is thought to be primarily maintained by disturbance such as fire. In this study we examined the plant community of 21 different oak savanna sites in western Lower Michigan, U.S.A., across a coarse disturbance gradient created by different management practices. Herbaceous community composition differed significantly across a variety of management approaches, while overall diversity remained similar. Indicator species analysis (ISA) identified several species commonly associated with mixed oak forest understories (e.g., Maianthemum canadense) as indicators for recently abandoned oak savanna sites, whereas the indicators identified for managed or heavily disturbed sites included common savanna-associates (e.g., Lupinus perennis). Variation in soil characteristics (C:N ratio and pH) and canopy cover may be driving these differences in plant community composition between management approaches. These results reinforce the importance of disturbance to Midwestern oak savanna ecosystems. Furthermore, if long-term management goals include encouraging the establishment and maintenance of herbaceous oak savanna-associated plant species, disturbance created through management activities, such as hand cutting, will likely yield better results over inaction, especially where using fire is not an option.
Pinus pungens (Table Mountain pine) stands are rare conifer-dominated communities that occur on xeric ridges and upper slopes throughout the central and southern Appalachian Mountains. At the northern end of this range, this uncommon forest community is essentially unstudied. Therefore, in 2006 I initiated a dendroecology study of three Pinus pungens stands growing in Pennsylvania to better understand their current conditions, histories, and likely future succession. These stands contained from four to 14 tree species with Pinus pungens or Quercus montana (chestnut oak) dominating the main canopy. Quercus coccinea (scarlet oak), Acer rubrum (red maple), or Nyssa sylvatica (black gum) were the primary species of the midstory. Kalmia latifolia (mountain laurel) was the principal understory shrub. Two of the communities had Pinus pungens and Quercus montana trees dating back into the mid-1800s and were likely heavily influenced by the charcoal iron industry of that century. Periodic fire was also part of their history. The other Pinus pungens community arose following abandonment of an agricultural field in the 1910s and fire does not seem to have been a factor in its ecological history. Two of the communities appear to be losing their Pinus pungens component as their understories are dominated by hardwood saplings or shrubs and there are no pine seedlings present. Perpetuating these and other Pinus pungens communities in Pennsylvania will require reducing the understory vegetation and creating suitable seed beds for Pinus pungens seedling establishment.
Biological invasion by nonnative species is considered one of the major threats to the global environment. Amur honeysuckle (Lonicera maackii) is a shrub introduced from Asia which has become invasive in Eastern deciduous forests of North America. An interesting aspect of the life-history of Amur honeysuckle is its extended leaf phenology. It leafs out earlier in the spring than most native shrubs and understory trees and loses its leaves later in the fall. Thus, Amur honeysuckle has the potential to alter the natural light environment and possibly impact native species, particularly spring ephemerals which are dependent on high light levels prior to canopy leaf-out. We tested the hypothesis that light levels are lower in sites with Amur honeysuckle relative to sites with native forest understory and quantified differences between sites. We found that light levels were significantly lower under Amur honeysuckle compared to natural understory, with the greatest reduction occurring during spring. Temperature at ground level was also lower under Amur honeysuckle than under the natural understory during spring. The extended leaf phenology of Amur honeysuckle alters both temperature and light intensity, which may increase both its success as an invader and its impact on native species.
Wiregrass (Aristida beyrichiana) is a dominant groundcover species that facilitates fire in southeastern U.S.A. pine savannas, thereby limiting woody plant cover and maintaining a herbaceous dominated understory. In December 1993 two of us planted a plot of wiregrass (Aristida beyrichiana) in the midst of fire-maintained little bluestem (Schizachyrium scoparium) longleaf pine (Pinus palustris) savanna in the outer Coastal Plain of South Carolina. The plot and the surrounding area burned three times in the following 20 y. Vegetation sampling carried out in late summer 2013 indicated wiregrass dominated the plot and the majority of little bluestem had disappeared. The wiregrass plot was comparatively open and grass dominated, whereas the surrounding formerly bluestem dominated stand had filled in with loblolly pine (Pinus taeda) saplings as well as hardwood trees and shrubs. In addition wiregrass had reproduced and established away from the original planted area, most noticeably within a soil-disturbed plow line. A subsequent prescribed fire in spring 2014 burned with higher intensity within the wiregrass plot than in the surrounding area. Our observations suggest suppression of woody plant encroachment by dense wiregrass in pine savannas even during long fire free periods, which should reduce the likelihood of transition to hardwood dominated ecosystems.
The introduced house centipede Scutigera coleoptera (L.) (Scutigeromorpha: Scutigeridae) is found throughout North America and is recognized as the only scutigeromorph in most of the United States and Canada. I report on the discovery of a population of the Japanese house centipede, Thereuonema tuberculata (Wood), from a military schoolhouse building in Ohio. Thereuonema tuberculata were collected for several years. Heightened scrutiny is called for on identifications of S. coleoptera throughout North America to differentiate this species from T. tuberculata.