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Often, ecological details are ignored in biogeographical analyses. I use the orchid flora of the Samoan islands to investigate the importance of such details for explaining biogeographical patterns, with special attention to habitat availability and long distance dispersal. Using data on orchid occurrence, island properties, and species traits, I examine putative ecological drivers of species distribution including many that are seldom considered in island biogeography. Simulations show that communities on younger islands are nested subsets of those on older ones. Epiphytic orchids, but not terrestrial orchids, are nested by altitude. Percent endemism is positively correlated with island age in a simple linear regression and positively correlated with altitude in a multiple linear regression that also included distance from the nearest island. ANOVA shows that orchids with high minimum elevations tend to be restricted to one or two islands, whereas widespread orchids tend to have low elevation requirements. These findings suggest that species traits, abiotic environment, cladogenesis, and/or repeated long-distance dispersal affect species distributions. More specifically, altitudinal habitat availability strongly affects orchid occurrence on any given Samoan island. Future contributions to this field should incorporate ecological parameters and identify relevant areas in which further empirical work is needed.
The characteristics associated with prey attraction and capture in pitcher plants are not well understood. Because of physiological constraints due to growth patterns and resource availability, pitcher characteristics should vary among seasonal cohorts and with pitcher age. We measured age-related changes in characteristics (funnel diameter, extrafloral nectar guides, extrafloral nectar concentration) and in prey capture of early- and mid-season cohorts of Sarracenia alata pitchers. Pitchers achieved their mature height before opening, and pitchers of the mid-season cohort were smaller than those produced early in the growing season. In both cohorts, extrafloral nectar concentration on the lip of the pitcher and the number of “secondary nectar guides” (an indication of hood coloration) were highest approximately 3 wk after pitchers opened. The rate of insect capture in both cohorts was highest approximately 3 wk after pitchers opened, corresponding with the peak in nectar concentration and the maximal number of secondary nectar guides observed. The mean intact insect capture from the four main collections (the three sampling periods for Cohort A and the single period for Cohort B) was significantly positively related to mean nectar concentrations for those collections. When pitchers were capturing at their maximal rate (3 wk after opening), prey capture per unit size per unit time was higher in the mid-season cohort even though nectar concentration was not significantly different than that in the early-season cohort. Furthermore, ants comprised a significantly greater proportion of intact insects captured by the mid-season cohort. The results of this study show that characteristics of pitchers and their effect on prey capture vary between seasonal cohorts and with pitcher age. Nectar appears to be an important attractant, and foraging insects may be attracted by nectar, coloration, or most likely by some combination of these and other characteristics. The physiological constraints and evolutionary pressures leading to these differences need to be examined.
Determining the impact of both environmental variation and developmental stage on plant-mycorrhizal associations is important, as both can shift the association along the mutualism-parasitism continuum. This study examines the effect of phosphorus level on the response of Allium vineale to mycorrhizae across all plant life stages, including plant fecundity and the relative allocation of resources to three different reproductive modes (flowers, asexual underground offsets, and asexual aerial bulbils). For A. vineale, the impact of mycorrhizae varies significantly with life stage, as an early growth depression at 1 mo was reversed by 15 mo, resulting in mycorrhizal plants having larger bulbs over all P levels and producing more bulbils and larger offsets than nonmycorrhizal plants at lower P levels. However the presence of mycorrhizae did not affect the relative allocation of resources among the three reproductive modes. These results emphasize the importance of long-term studies of plant-mycorrhizal interactions that include fecundity estimates. In addition, they indicate that spatial variation in nutrient availability in the field has the potential to shift the overall effect of mycorrhizae from beneficial to neutral, with greater benefits found in sites with lower phosphorus levels.
Comprised of largely non-commercial, xeric, oak-dominated forests, the Cross Timbers in Arkansas have been heavily altered over the last two centuries, and thus only scattered parcels of old-growth timber remain. We inventoried and mapped two such stands on Fort Chaffee Military Training Center in Sebastian County, Arkansas. The west-facing Christmas Knob site is located on an isolated hill, while the southerly-facing Big Creek Narrows site is on a long, narrow rocky outcrop called Devil's Backbone Ridge. These sites occupied rocky, south- to southwest-facing sandstone-dominated slopes, with primarily post oak (Quercus stellata) and blackjack oak (Q. marilandica) overstories. Post oak dominated the largest size classes at both sites. Increment cores indicated that some post oaks exceeded 200 y of age, and tree-ring dating also confirmed an uneven-aged structure to these stands. Both locations had irregular reverse-J shaped diameter distributions, with gaps, deficiencies, and excesses in larger size classes that often typify old-growth stands. On average, the post oaks at the Big Creek Narrows site were taller, larger in girth, and younger than those on the Christmas Knob site, suggestive of a better quality site at Big Creek. The application of neighborhood density functions on stem maps of both sites found random patterns in tree locations. These stands are very similar in their structure to old-growth examples in other parts of the Cross Timbers ecoregion.
A study was conducted to characterize termite colonies on the Nature Conservancy's Tallgrass Prairie Preserve Cross Timbers habitat in northeastern Oklahoma. The two test sites were established on a prescribed-burn area and no-burn area of the Cross Timbers habitat. Termites were identified through both morphological and molecular analyses. Foraging areas of five colonies were delineated. Numbers of termites in foraging groups, estimated using the ‘weighted mean model’, ranged from 103,093 (±7081) to 422,780 (±19,297) for Reticulitermes flavipes within the prescribed-burn area, and 44,179 (±4879) to 207,141 (±9190) for R. hageni within the no-burn area. Soldier percentages were determined for each foraging group. Estimates of foraging areas and populations are compared with those from previous studies in dissimilar tallgrass prairie habitats. Improved understanding of termite colony densities in various natural habitats provides an increased understanding of termite input in rural areas and could aid in the development of management strategies.
Leaf detritus in streams fills dual resource roles as habitat and as food. Unless retained by some structural component, detritus gets transported to downstream reaches out of the local system. Low gradient sandy-bottomed streams retain leaf detritus via burial in sand, but this mechanism of retention limits the availability of detritus as a resource for the benthic community. We hypothesized that burial of leaf litter in sand would impact invertebrate colonization by reducing density and richness on leaf litter. We conducted a short-term experiment (i.e., 2 wk) in a sandy-bottom stream in which leaves were subject to either burial in sandy substrate, exposure to the water column, or a sequential combination of both. Results showed that 2 wk burial of leaf litter significantly impacted the colonization of benthic invertebrates. Burial or exposure status of leaves at the time of collection represented the major factor influencing invertebrate abundances on leaf litter. Leaves exposed to the water column had the highest abundance of invertebrates, dominated by collector-gatherers, that suggests the primary role of leaf litter as refugia in this system. Burial of leaf litter in sand had a significantly negative effect on invertebrate colonization of leaf litter. Furthermore, no difference existed in invertebrate colonization on leaf litter that had never been buried versus leaf litter that had been buried for 1 wk and then exposed and collected after a week in the water column. This suggests short-term burial of leaf litter does not influence colonization by invertebrates once leaf litter is exposed to the water column. The results of this study suggest that the benthic colonization on newly exposed leaf litter is rapid, potentially due to a lack of habitat structure availability in the sandy-bottomed stream.
The fluted kidneyshell Ptychobranchus subtentum (Say, 1825) is a candidate for listing under the Endangered Species Act by the US Fish and Wildlife Service. Fecundity, fish hosts, and selected population demographics were determined during 2005–2006 for the fluted kidneyshell in the upper Clinch River, Hancock County, Tennessee. Females were fertilized in Aug. within a 5 d period and contained viable glochidia about 4 wk later. As the embryos began to develop, the marsupium gradually changed color from white to dark brown. Glochidia were contained within conglutinates that resemble Simuliidae pupae likely to attract benthic insectivorous fish and were held over winter and released in May. Fecundity was positively related to mussel length (r2 = 0.81) and ranged from 43,000 to 500,000 glochidia. Eight species of darters (Etheostoma spp. and Percina spp.) were infested with glochidia in the laboratory to examine potential hosts and host suitability. Juveniles transformed on bluebreast darters E. camurum and dusky darters P. sciera and previously reported hosts: rainbow darters E. caeruleum and fantail darters E. flabellare. In addition, fantail darters and rainbow darters were infested with glochidia from two river systems. The median time of glochidial metamorphosis did not differ significantly between the two mussel populations. The observed ratio of adult females to males (1.9∶1) in the Clinch River differed significantly from 1∶1. Based upon thin-sections, individuals live to at least 26 y and females become sexually mature at age five.
The extirpation of native fishes is a major concern in North America, and an understanding of population trends of imperiled fishes is critical to their management and conservation. Mountain sucker Catostomus platyrhynchus is a stream fish native to the Intermountain Region of western North America, and populations in the Black Hills of South Dakota represent the easternmost range of the species. Recently, stream surveys raised concerns about the status of mountain sucker populations in South Dakota. The purpose of this study was to document the current distribution of mountain sucker in the Black Hills of South Dakota for comparison with historic records. We analyzed stream fisheries survey data collected between 1960 and 2010 and found that mountain sucker density generally declined at three nested spatial scales: sample reach, stream, and watershed. At 14 sample reaches and two streams mountain sucker appear extirpated, whereas in remaining areas they persist in varying densities. In 2009–2010, populations exceeding densities of 0.01 fish·m−2 persisted only in Whitewood, Elk, Boxelder, and Bear Butte Creeks, and tributaries to Upper Rapid Creek. Our study documents the decline of a native fish in the Black Hills of South Dakota, and a comprehensive ecosystem management approach is needed to mitigate further loss of mountain sucker and co-occurring native species, while at the same time maintaining a highly valued non-native salmonid fishery.
Ironcolor shiner Notropis chalybaeus is generally absent from groundwater-dominated systems throughout its range; however, a relict disjunct population occurs within the spring-fed upper reaches of the San Marcos River in central Texas. We conducted monthly seine collections within the restricted 2.2 km headwater range of the species to assess food habits and reproductive life history within a unique spring-run environment. Prey items were dominated by aquatic insects including Diptera (16% by weight), Ephemeroptera (13%), and Odonata (5%), as well as terrestrial insects (9%). The population consisted of four age groups with a maximum life span of 2.5 y. Reproductive ecology showed a protracted spawning season ranging Mar.–Dec. during which multiple clutches were produced. Reproductive maturity was reached at approximately 1 y (36 mm SL), mean mature oocyte diameter was ∼0.8 mm, and number of mature oocytes per clutch ranged 46–326. Comparisons between ironcolor shiner populations in the San Marcos River and thermally dynamic Marshalls Creek of Pennsylvania revealed mature female size was larger (T38 = 10.48, P < 0.01) and mature oocyte diameter smaller (T38 = 16.87, P < 0.01) in the upper San Marcos River. Literature accounts regarding ironcolor shiner reproductive ecology suggest a latitudinal trade-off between reproductive season length and oocyte size. Our findings provide further evidence for the roles of photoperiod and water temperature in structuring the reproductive seasonality of spring-dwelling fishes, specifically the lack or delay of terminating cues in stenothermal waters. In this manner, aquifer depletion and alteration of thermal regimes threaten spring-dwelling fishes by disrupting naturally occurring reproductive cues.
Red-winged Blackbirds (Agelaius phoeniceus) may be more likely to desert nests parasitized by Brown-headed Cowbirds (Molothrus ater) when they interact with the parasite, because desertion frequencies are higher at naturally parasitized nests than at artificially parasitized nests in some brood-parasitic hosts. We experimentally parasitized blackbird nests in southern Manitoba with cowbird model eggs and presented taxidermic mounts of adult female cowbirds near their nests. We observed no desertion, which is possibly attributable to constraints of a shorter breeding season at this latitude. We also compared rejection frequencies for blackbirds when a mounted female cowbird was placed near the nest to rejection frequencies recorded when (1) no model egg was added, (2) a model egg was added but no mounted cowbird was presented, and (3) a model egg was added plus presentation of a mount of a non-parasitic and non-threatening species, the Fox Sparrow (Passerella iliaca). Blackbirds struck the cowbird mount more often than the sparrow mount, but responses to the cowbird mount did not influence acceptance or rejection of the model egg. Blackbirds apparently engage in the least costly form of anti-parasite defense (aggression) and accept the costs of acceptance instead of those of renesting during a short breeding season.
Streamers of hanging plant debris (nest tails) are commonly used for nest concealment by tropical Tyrannid flycatchers. Of the 35 species of Tyrannid flycatchers that regularly occur in temperate North America, only the Acadian flycatcher (Empidonax virescens) retains use of nest tails. To better understand the prevalence and possible function of nest tails in temperate breeding Acadian flycatchers, we investigated 145 nests in two habitat types (deciduous and hemlock (Tsuga Canadensis) dominated) in southwestern Pennsylvania in 2006–2007. The primary constituent of nest tails was catkins of oak (Quercus sp.) and American beech (Fagus grandifolia) along with other plant debris entangled in arthropod silk. Debris availability was generally sparse but appeared more common on nest as opposed to randomly selected branches. An index of nest tail “prominence,” involving both the length and number of tails, was negatively related to nest height. Variation in nest survival rates was poorly explained by nest tail prominence, and no models evaluated substantially outperformed the null model. Thus, we provide a detailed quantitative description of Acadian flycatcher nest tail characteristics in a northern temperate environment but an understanding of their function in this environment remains elusive.
Rodent prey contained in two temporally distinct collections of Barn Owl (Tyto alba) pellets from the same roost in southeastern Washington state (USA) differ in terms of taxonomic abundances. Deer mice (Peromyscus maniculatus) dominate the fauna in the pellet sample deposited while much of the landscape was productive wheat field, and voles (Microtus spp.) are a distant second. The fauna in the pellet sample deposited after 20% of the surrounding landscape was placed in soil bank and converted to a grass non-producing field is dominated by voles with deer mice a close second. The coincident changes in local vegetation and in the rodent fauna are causally as well as temporally interrelated. Previous local studies have focused on the agricultural economics of coincident shifts in agricultural practices and rodent faunas. Results presented here indicate potential benefits to owl faunas of changes in agricultural practices and suggest that study of curated owl pellet faunas collected decades ago may reveal much about the long-term history of anthropogenic influences on rodent faunas.
In many pronghorn populations there exists uncertainty about which factors most affect survival rates. Also, although pronghorn within the same population might exhibit both migratory and non-migratory behaviors, few studies have assessed whether migration status affects survival rates. We determined cause-specific mortality for 134 adult, radio-tagged pronghorn in southwestern North Dakota, 2004–2008, estimated survival rates, and examined support for 11 a priori models containing combinations of year, age, sex, season, and migration status. We documented 102 deaths (52 females, 50 males) of radio-collared pronghorn. Over half of the observed mortality was due to hunter harvest (58%). Migration status was not an important determinant of pronghorn survival when compared to other factors. A model containing a season × sex interaction was most supported. Seasonal survival rates were >0.90 for males and females except in fall when female survival rates were reduced to 0.8, and male survival was less than half (0.42), which was due to hunting mortality. Survival rates were highest in winter, which might have been facilitated by mild winter weather during our study. Given the important role of harvest on pronghorn survival, biologists can best manipulate pronghorn abundance, and reduce landowner conflicts, through hunting license allocation.
Changes in ungulate distribution can alter competitive interactions, plant communities, risks of zoonotic disease transmission, and availability of animals for harvest. We used annual aerial survey data for northern Yellowstone elk in Montana and Wyoming, USA to evaluate factors influencing distribution and group sizes during 1987–2009 in four sectors of elk winter range corresponding to river watersheds with different minimum elevations and snowpacks. Our best logistic regression model suggested the proportion of elk occupying the upper elevation sector decreased following wolf restoration and increased snowpack. The proportion of elk occupying the lower elevation sector increased following wolf restoration and as snowpack increased at higher elevations. Linear regression suggested group sizes increased in the lower elevation sector after wolves were restored. Concurrent demographic and movement studies suggest these changes resulted primarily from the attrition of elk from high snow areas in Yellowstone National Park due to predation, and increased survival and recruitment of elk in lower snow areas outside the Park in Montana following a substantial reduction in hunter harvest. Fitness trade-offs between foraging conditions and the risks of predation (or harvest) as constrained by snow vary considerably among elk populations in the Yellowstone ecosystem.
Few researchers have used radiotelemetry to study spatial organization in beavers (Castor canadensis) given limitations in available radio-attachment methods for the species. During Mar. 2005–Sept. 2006, we attached tail-mounted transmitters to 46 beavers from 10 colonies in an unexploited beaver population in southern Illinois. We used radiotelemetry to quantify sizes and percentage overlap of composite and seasonal home ranges and core areas of beavers and tested for differences by age and sex. Composite home ranges and core areas averaged 25.5 ha and 3.9 ha in size, respectively, and did not differ between age and sex (P > 0.41). There was no difference in seasonal home range sizes between age or sex (P > 0.14); however, pooled home range sizes differed by season and year (P = 0.007). Seasonal core area size did not differ among age, sex, or season (P > 0.10). Percentage of seasonal home range overlap approached significance among seasons (P = 0.077), and seasonal core area overlap differed by season (P = 0.005). Mean composite colony home ranges and core areas were 22.7 ha and 3.5 ha in size, respectively. Nine out of 11 colonies had overlapping home ranges with ≥1 neighboring colony (x ¯ overlap = 9.8 ± 1.5%) and to our knowledge represents the only known documented colony home range overlap in this species.
The eastern sand darter (Ammocrypta pellucida Agassiz) is a small (<7 cm) bottom dwelling fish that inhabits rivers with clean sand substrates. Siltation and degradation of its riverine habitat caused the species to become rare throughout its entire range, a geographic area originally extending from the St. Lawrence River and the Lake Champlain drainages to southwestern Ontario, southeastern Michigan, and throughout much of the Ohio River basin to eastern Illinois and south into Kentucky. Ammocrypta pellucida was documented as being abundant in the Maumee River (western Lake Erie drainage) in the late 1800s; but, with increased erosion and siltation in this basin, it has not been reported from the Ohio portion of the Maumee River mainstem since 1944. During field observations in Nov. 2009, we used seines and electroshocking to capture (and release) 18 A. pellucida from five 10 m2 sites near Antwerp, Ohio. This represented the first record of this species in the Ohio portion of the Maumee River mainstem in 65 y. In Sept. 2010, using similar and standardized field techniques, a total of 24 eastern sand darters were observed in six out of twelve sites in 4.8 km of the Maumee mainstem. At least two age classes were present. Four 10 cm deep sediment cores were taken at each site and analyzed for particle size distribution and organic matter content. Eastern sand darter abundance was positively correlated with fish species richness, fish diversity, medium sand and medium fine sand substrates. Documented reductions in sediment load in the Maumee since the late 1970s, coincident with changes in upstream agricultural practices, may have helped reduce silt from sandy areas in the Maumee mainstem, promoting the recolonization by this silt-intolerant species from upstream refuges. Our results may help guide conservation efforts for this Species of Special Concern in Ohio.
Fruits and their seeds are ingested by many carnivores, but few studies have quantified the effect of ingestion by carnivorous consumers on seed germination. Here, we examine effects of bear frugivory on the germination of three fruit-producing species. Specifically, we compare germination of gut-passed seeds to that of seeds mechanically-extracted from fruits and seeds that remained within fruits. For all species, germination in the mechanically-extracted and gut-passed treatments exceeded that of the whole fruit treatment. Our results suggest that for these three species, passage through the digestive tract of a bear positively influences germination by removing seeds from pulp, but that gut-passage per se does not increase germination success.
We describe the removal (predation) of a black-capped vireo (Vireo atricapilla) nestling by a female greater arid-land katydid (Neobarrettia spinosa) in southwest Texas. The event was captured with a nest camera during night in Jun. 2010. Neobarrettia species are known to be aggressive and carnivorous, but this is the first report of a katydid depredating a songbird nest.