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While ecologists have studied succession for well over 100 y, there has been little characterization of diversity patterns in nonplant organisms or their interactions across successional gradients. In this study we examined herbaceous vertical vegetation structure and diversity in plants, arthropods, and arbuscular mycorrhizal fungi (AMF) in three Great Lakes sand dune chronosequences. Plant species richness increased linearly across the primary successional gradients at the three sampling sites, while plant vertical structure remained constant. Total arthropod abundance and species richness were positively associated with plant vertical cover, while AMF spore abundance and morpho-type richness were positively associated with plant species richness. Carnivore and herbivore functional groups of arthropods responded differently to plant vertical cover and species richness. Diversity across early primary successional gradients does not consistently increase among different trophic levels, and the vertical structure of vegetation can be important in explaining richness and abundance in other trophic levels across a successional gradient.
The study of floral traits and pollination for the plant genus Phlox has historically been focused on either surveys of general pollinator affinities across the genus or detailed research on pollinator-mediated evolution of floral color in a single species (Phlox drummondii). The purpose of this study was to explore a different kind of trait – floral scent – in Phlox divaricata, a species noted for its strong scent. Specifically, we predicted the diel emission patterns of floral scent might covary with the daily abundance of diurnal moths, identified in a previous study as the most important pollinators in a Konza Prairie population of P. divaricata. Consistent with this prediction, we documented peaks in median floral scent emissions at 1000–1200 and 1930–2130, coinciding with peaks in moth visitation and resulting seed production. Two groups of scent compounds contributed to this pattern; linalool and its associated lilac aldehyde/alcohol compounds (especially lilac aldehyde B) contributed a greater proportion to scent at 1000–1200, while aromatic compounds (including benzaldehyde and benzyl acetate) contributed a greater proportion to scent at 1930–2130 and other afternoon time periods. These volatiles are known floral attractants for several lepidopteran pollinators, including noctuid moths. However, there is an additional peak in pollinator abundance (Hemaris diurnal hawkmoths) and seed set at a time when scent production is relatively low (1400–1600) suggesting additional factors mediate both pollinator behavior and floral volatile emissions. Future studies of P. divaricata should test for the presence of destructive floral enemies that might be attracted by floral volatiles during mid-afternoon periods, as well as the importance of visual floral traits (color, shape) in attracting diurnal moths, an important functional group of pollinators that has received minimal attention in North America.
Phytophagous insects from different feeding guilds may compete indirectly via altering the chemical defenses or nutritional quality of their shared host plants. Gall-formers are understudied in this context but may be susceptible to this mode of competition early in their life history, when they may be particularly sensitive to changes to the specific reactive tissue needed for gall development. Here, we conducted a natural experiment to investigate the effect of folivory of Canada goldenrod, Solidago altissima, by Trirhabda beetles on gall induction success for the goldenrod gall fly, Eurosta solidaginis. We monitored oviposition events and gall development on individual Solidago ramets at sites differing in their levels of Trirhabda folivory. We found a strong inverse relationship between Trirhabda leaf damage and successful gall induction rates. These results suggest Trirhabda beetles may negatively impact Eurosta demographics and highlight the need for further study on how factors affecting gall induction may influence the structure of insect communities.
Habitat fragmentation can intensify consumer attack on plants if herbivores stay longer, eat more extensively, or exhibit higher density at low resource availability; it may also reduce attack if consumers are dispersal limited and therefore fail to forage on smaller or more distant patches. Here we test these alternatives with a large-scale grassland fragmentation experiment, comparing vertebrate and invertebrate herbivory on seedlings of an oak species of central North America (Quercus ellipsoidalis) experiencing recruitment difficulties across its range. All seedlings suffered significant herbivore-based defoliation regardless of experimental context, confirming the influence of consumer pressure on recruiting oaks on contemporary landscapes. However, vertebrates and insects responded differently to fragmentation. Vertebrate grazing was unaffected by patch size or isolation – remnants were either periodically visited by foraging deer or colonized by small mammals that occasionally attacked seedlings. In contrast invertebrate consumers significantly reduced seedling growth via the effects of defoliation, but these effects decreased on smaller and more isolated patches. This was associated with a negative influence of patch size on the diversity of herbaceous vegetation, with reduced plant diversity correlated with the reduced abundance and diversity of several generalist insect herbivore groups. Our results demonstrate fragmentation has the potential to affect the identity and intensity of herbivore attack on oaks, although whether the reduced insect attack we observed in isolated remnants is sufficient to increase juvenile survivorship remains to be tested.
To determine if manipulation of milkweed's natural phenology would increase monarch reproduction, strips were mowed in fields in upstate New York in early Jul., late Jul., and mid Aug., 2006, for comparison to an unmowed control. Common milkweed (Asclepias syriaca) was then monitored from Jul. 29 through Sep. 24 for plant height, vegetative stage, level of herbivory, condition, monarch eggs and larvae, and the position of eggs on leaves and stems. We found mowing on Jul. 1 and 24 spurred the regrowth of milkweed and sustained a more continuously suitable habitat for monarch oviposition and larval development than the control. Mowing on Aug. 17 proved too late for recovery of the milkweeds. Significantly more eggs were laid on the fresh resprouted milkweeds than on the older and taller control plants. In the strips mowed on Jul. 1, peak egg densities occurred in late Jul.; in the strips mowed in late Jul., peak egg densities occurred in early to mid Aug. Depending on the timing of mowing, the milkweed plant height, developmental stage, and condition differed. As predicted, the mowing of fields with Asclepias syriaca extended the monarchs' breeding season and increased overall monarch reproduction. However, timing of mowing was critical and must be determined empirically for different milkweed species and in different locations. This mitigation procedure could be fostered along roadsides, along edges of fields and pastures, in USDA conservation reserve program lands, and along power lines and other rights of way.
Interspecific competition can influence patterns of habitat use by small mammals. We examined the effects of interspecific interactions on habitat use by prairie voles (Microtus ochrogaster) and meadow voles (M. pennsylvanicus), two species that co- occur in grass habitats in east-central Illinois, but differ in their tolerance of sparse cover (prairie voles are more tolerant than meadow voles of sparse cover). We conducted a species-removal study in open populations, a species-addition study with enclosed populations, and dyadic encounters in the field, using mown and unmown grass areas, and in the laboratory. In the species-removal study, we found a positive response of prairie voles to removal of meadow voles from unmown grass habitat, and of meadow voles to removal of prairie voles from mown grass habitat. Additionally, when both species were present in control sites, prairie voles were most abundant in mown grass and meadow voles in unmown grass. In enclosures we confirmed greater tolerance of sparse cover by prairie voles (similar numbers of individuals in mown and unmown sites) than meadow voles (more individuals in unmown than mown sites), and these patterns were unaffected by addition of the other species. In dyadic encounters conducted in the field, male prairie voles were dominant over male and female meadow voles in mown grass habitat, whereas female meadow voles were dominant over male and female prairie voles in unmown grass habitat. These dominance relationships, which are consistent with the known social systems of the two species, were not observed when dyadic encounters were conducted in the laboratory in a neutral arena that lacked structural habitat cues. Taken together, our data confirm differences between prairie voles and meadow voles in tolerance for sparse cover and indicate a role, though limited, for interspecific competition in reinforcing patterns of habitat use by each species.
Gaps between distributions of closely related species have been noted in the literature but little empirical research exists to explain these patterns. One hypothesis is poor habitat quality occurs within the gaps and therefore prevents species from inhabiting these areas. Multiple examples of gaps between species distributions can be found among different species of pocket gophers. The objective of this research was to analyze a zone of separation between Geomys bursarius and Cratogeomys castanops in southwest Kansas. Habitat suitability maps were produced using Maxent (3.3.2) for each species throughout the study area. Values of habitat suitability and important habitat variables were compared between locations within the zone of separation and presence localities. The most important variable for predicting habitat suitability for G. bursarius was percent sand, while both percent sand and clay were important for C. castanops. Habitats within the zone of separation were significantly less suitable compared to presence localities. Also, important habitat variables (percent sand and clay) were significantly different at presence localities for both species compared to within the zone of separation. These results suggest the zone of separation between populations of G. bursarius and C. castanops is maintained by a trough of lesser quality habitat.
We studied the seasonal home range of individual white-tailed deer (Odocoileus virginianus) as it related to landscape pattern (forest-edge density; the ratio of agriculture to forest), local deer density, and harvest intensity in a population managed for control of chronic wasting disease in south central Wisconsin. The ratio of agriculture to forest showed strong positive correlation to home range size for most age and sex classes, while forest edge density was inversely related to home range size for adult females. Individual home range size proved largely independent of density and harvest intensity. It is likely that socio-spatial factors (i.e., fidelity) and the availability of food and cover influence home range size more strongly than hunting pressures or density reductions. This suggests localized reductions may create areas of low density without changing the behavior patterns of the population. Our findings suggest a more spatially-targeted effort to reduce density, by removal of social groups, in areas where chronic wasting disease is present may provide better efficacy in reducing potential for disease transmission.
Overabundance and associated impacts of deer on mainland forests of the United States have been topics of extensive investigation and management discussion. Conversely, deer populations on barrier islands have been less studied with few investigations of their impacts on maritime evergreen forest. We investigated how deer influenced understory vegetation and oak seedling survival following culling of deer. In 2007 twenty 10 m × 10 m paired exclosure and control plots were established within a 77.3 ha protected area on Bald Head Island, North Carolina. Vegetation was sampled in 2011. We determined deer did not affect understory vegetation and oak survival was low and not influenced by deer. Chronic over-browsing (i.e., ‘ghost of herbivory past’) was unlikely because deer were not abundant on Bald Head Island until the 1990s, oak seedlings were observed where light was abundant, and deer were observed using other cover types on the island. Continued monitoring of the forest understory and maintenance of deer at the current population level will help conserve maritime forest on Bald Head Island.
North American river otters (Lontra canadensis) frequently visit latrines where they deposit urine, feces, and anal secretions as olfactory signals. River otter scat was collected from latrines to identify prey at the Emiquon Preserve and the Emiquon National Wildlife Refuge located along the Illinois River near Havana and Lewistown in Fulton County, Illinois. Remains of prey from dissected scats were compared to osteological resources to taxonomically identify the remains. Fish were present in 85.4% of the dissected samples. Common carp (Cyprinus carpio) were the most common fish preyed upon during the study, occurring in 69.8% of all dissected samples. Crayfish were present in 77.1% of samples. Amphibians, insects, filamentous algae, green-winged teal (Anas crecca) or blue-winged teal (A. discors), and muskrat (Ondatra zibethicus) were also consumed. The minimum number of individuals (MNI) consumed was also determined based on the prey remains present. The results of a two-tailed Fisher's exact test demonstrated there were significant differences in the percentage of prey consumed by otters at Emiquon and in previous studies conducted in Whiteside County, Illinois, and Alberta, Canada.
Bobcats (Lynx rufus) are a native carnivore of Ohio, but by 1850 were extirpated or nearly so following pioneer settlement of the state. The first modern record of a bobcat in Ohio was an adult male killed in 1946. Distribution accounts indicate that population re- establishment began around 2000. Today the bobcat is protected, and verified sightings, camera surveys, and genetic analyses point to two subpopulations: a fast growing, self-sustaining eastern subpopulation, and a more slowly growing southern subpopulation. We evaluated stomach contents of 120 adult and subadult bobcat carcasses to help understand the disparity in subpopulation growth rates, and inform proper bobcat management. We identified prey species morphologically. We quantified prey species taken and converted their frequencies to caloric intake estimates. We calculated dry weight estimates of prey groups and compared them between bobcat age classes, sexes, regions, and across seasons. We examined regional diet differences further by calculating diet and condition indices. Eastern cottontail (Sylvilagus floridanus) occurred most often. White-tailed deer (Odocoileus virginianus) supplied the greatest caloric value. Small rodents and insectivores were the most common prey group. Adults consumed more, as defined by weight, meso-mammals and large rodents than subadults. Diet composition did not differ between sexes. Weight of large mammal intake differed significantly between winter and summer, being greater in winter. Diet composition and prey group weights did not differ regionally. Dietary niche breadth of the southern subpopulation indicated more even consumption of prey groups than the eastern, whereas food niche overlap between regions was high. The condition index of eastern and southern bobcats also did not differ. We present the first rigorous analysis of bobcat diet in Ohio, and infer that diet is not a likely driver of disparate subpopulation growth rates of this recovering species.
Biologists often manage grassland habitat for ring-necked pheasants (Phasianus colchicus) through provision of the grasses and forbs that support the invertebrates on which they forage. However, specific information pertaining to invertebrate prey selection by ring-necked pheasant broods is lacking. To address this, we used radio-telemetry to locate pheasant roost sites where we collected pheasant chick droppings. We then identified characteristic fragments of invertebrates in each dropping sample to family and order to calculate percent composition of each. Next, we sampled invertebrate abundance near to sites where droppings had been collected using a standard sweep netting protocol. Invertebrates found in chick droppings were compared with the diversity of invertebrates available on the landscape. Curculionidae [weevils (Order Coleoptera)] were present in all droppings sampled, and they were the most frequently consumed invertebrate taxa by seven of the nine broods sampled. The remaining two broods consumed Formicidae [ants (Order Hymenoptera)] most frequently. All broods significantly selected Coleoptera more than expected by their availability, and two broods significantly selected Hymenoptera more than expected by their availability. Habitat management practices that result in greater abundance of these species on the landscape should be beneficial to pheasants.
The diel diet composition and feeding periodicity of Luxilus cornutus (common shiner), Exoglossum maxillingua (cutlip minnow), Semotilus corporalis (fallfish), and Notropis hudsonius (spottail shiner) were examined in the Salmon River, New York over a 24 h period during the summer. Chironomids were the major prey of common shiner (60.6%) and cutlip minnow (54.7%), whereas terrestrial invertebrates (30.0%) and amphipods (38.4%) were the primary food of fallfish and spottail shiner, respectively. Diet overlap was high between common shiner and cutlip minnow (Morisita's index = 0.88) and moderate between fallfish and common shiner (0.54) and fallfish and cutlip minnow (0.50). Diel temperal variation in diet composition was greatest (0.64) for spottail shiner. Three species exhibited diel variation in food consumption. Fallfish had a distinct feeding peak, whereas peak food consumption of common shiner and cutlip minnow occurred over a more extended period. Spottail shiner did not have a distinct feeding peak but food consumption was highest from 2400 to 0800 h. Each of the four species exhibited some degree of variation in their diel feeding ecology in regards to either diet composition or food consumption.
Anthropogenic activities have greatly altered the natural flow regime of lotic ecosystems in many ways, including dams and culverts, which restrict sediment transport and fragment fish habitat. Sculpins, Cottus spp., are an important food-web link between macroinvertebrates and larger stream fishes and are greatly affected by culverts. Results from a previous study indicate a substantial increase in the relative abundance of mottled sculpin, Cottus bairdii, was observed upstream of a renovated road-stream crossing during the first season after construction. Redistribution of this nature from a putatively sedentary species would have required substantial movement. Our objectives were to quantify post-restoration mottled sculpin movement and habitat use in a restored stream reach. The extent of post-restoration mottled sculpin movement and habitat use were directly measured using telemetry of Passive Integrated Transponder (PIT) tag-marked fish. The maximum linear distance moved by a marked mottled sculpin was 839 m; 23% of marked mottled sculpin moved >100 m. The number of detections of marked mottled sculpin in each segment was significantly correlated with the amount of small wood (5–10 cm diameter). Increased distribution of mottled sculpin in previously unavailable upstream habitats coupled with substantial post-restoration movement distances provides new insight on their potential for redistribution following habitat reconnection, which is an important consideration for stream restoration projects.
The eastern massasauga rattlesnake (Sistrurus catenatus) is a threatened species that occurs in habitats frequently targeted by prescribed burns. There have been reports of massasauga mortality as a result of prescribed fires, but little is known regarding the indirect effects of fire on this species. The objective of this study was to monitor massasaugas during a prescribed fire to assess direct and indirect effects. We initially implanted radio transmitters in 13 massasaugas inhabiting an area targeted for periodic prescribed fires and tracked them following a prescribed fire to determine burn-related mortality and behavioral influences. Data loggers, temperature sensitive paint, and measuring posts were used to record detailed fire data. Of the five snakes on the burn unit at the time, two died as a result of the fire. No differences were observed in daily movements and home range sizes between burn categories (in the burn, same site not in the burn and at a nearby unburned site). Snakes on and off the burn unit at the same site exhibited the same habitat preference for wetland habitats, whereas snakes at the control site preferred herbaceous areas. Slight differences were observed in microhabitat selection related to litter depth, surface light intensity, distance to water, and surface temperature. The snakes did not appear to alter their seasonal activities as a result of the prescribed fire. The results of this study suggest ways to minimize impacts from prescribed fires on massasauga populations.