Effects of grazing on vegetation structure, prey availability, and reproductive success of Grasshopper Sparrows

2005 ◽  
Vol 76 (4) ◽  
pp. 345-351 ◽  
Author(s):  
Benjamin Sutter ◽  
Gary Ritchison
Keyword(s):  
Reproductive Success ◽  
Vegetation Structure ◽  
Prey Availability

scholarly journals Vegetation structure and decreased moth abundance limit the recolonisation of restored habitat by the European Nightjar

2018 ◽  
Vol 3 ◽  
pp. 25-39 ◽  
Author(s):  
Nathalie Winiger ◽  
Pius Korner ◽  
Raphaël Arlettaz ◽  
Alain Jacot
Keyword(s):  
Vegetation Structure ◽  
Habitat Restoration ◽  
Stand Structure ◽  
Prey Availability ◽  
Population Declines ◽  
Major Transitions ◽  
Slowing Down ◽  
Open Forest ◽  
Mineral Soils ◽  
Management Recommendations

Woodland ecosystems of Europe have undergone major transitions in the last centuries. Changes in land use and the loss of natural forest dynamics have often led to structurally poor, uniform and dense stands. Not surprisingly, open forest species relying on a heterogeneous stand structure have suffered dramatic population declines. The European Nightjar Caprimulguseuropaeus, a nocturnal insectivorous bird, has undergone such a decline in its main Swiss stronghold in Valais. Despite the species’ potential to colonize new sites and habitat restoration measures implemented since 2001, recolonisation of restored sites has not taken place, suggesting problems with the current habitat restoration strategy. In order to refine management recommendations, we compared habitat structure and moth abundance, a key Nightjar food source, at sites that are still occupied and at sites that had been abandoned but have recently been restored. Vegetation structure was more heterogeneous and moth abundance greater at occupied than at abandoned sites. More specifically, occupied sites harboured a greater coverage of bare ground, while abandoned sites exhibited a higher amount of regeneration and intermediate shrub layer. The occurrence of natural perches was also higher in occupied sites. Abandoned sites are thus characterised by lower prey abundance and denser vegetation cover, the combination of which is likely to lead to lower prey availability for hunting Nightjars. Restoration action would benefit from maintaining snags and dead branches and by targeting unproductive habitats characterised by mineral soils, thereby slowing down regeneration and shrub regrowth. For future successful management of Nightjar habitats, it seems thereby essential trying to find the balance between actions that allow opening the lower and mid-strata of the forest while sustaining high moth populations.

Invertebrate prey availability limits reproductive success but not breeding population size in suburban House Sparrows Passer domesticus

Ibis ◽  
2015 ◽  
Vol 157 (3) ◽  
pp. 601-613 ◽  
Author(s):  
Will J. Peach ◽  
John W. Mallord ◽  
Nancy Ockendon ◽  
Chris J. Orsman ◽  
William G. Haines
Keyword(s):  
Reproductive Success ◽  
Population Size ◽  
Prey Availability ◽  
Passer Domesticus ◽  
Breeding Population ◽  
House Sparrows ◽  
Invertebrate Prey

scholarly journals Eastern Baltic cod recruitment revisited—dynamics and impacting factors

2016 ◽  
Vol 74 (1) ◽  
pp. 3-19 ◽  
Author(s):  
Friedrich W. Köster ◽  
Bastian Huwer ◽  
Hans-Harald Hinrichsen ◽  
Viola Neumann ◽  
Andrei Makarchouk ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Large Scale ◽  
Prey Availability ◽  
Stock Assessment ◽  
Future Research ◽  
First Feeding ◽  
Spawning Areas ◽  
The Baltic ◽  
Eastern Baltic ◽  
Baltic Cod

The Eastern Baltic cod abundance started rapidly to increase in the mid-2000s as evidenced by analytical stock assessments, due to increased recruitment and declining fishing mortality. Since 2014, the analytical stock assessment is not available, leaving the present stock status unclear and casting doubts about the magnitude of the recent increase in recruitment. Earlier studies identified main factors impacting on cod reproductive success to be related to the loss of two out of three spawning areas in the 1980s caused by lack of major Baltic inflows with a concurrent reduction in salinity and oxygen. Other important factors include prey availability for first-feeding larvae, egg predation by sprat and herring and cannibalism on juveniles, all in one way or the other related to the prevailing hydrographic conditions. These factors cannot explain increased reproductive success in the last decade, as the period was characterized by an absence of large-scale Baltic inflows since 2003 and persistent anoxic conditions in the bottom water of the deep Baltic basins. This questions the perception of the increased recruitment in later years and challenges our present understanding of cod recruitment dynamics in the Baltic Sea. In this contribution, we review evidence from the recent literature supplemented by information from latest research cruises to elucidate whether cod reproductive success indeed has increased during the last decade, and we suggest the key processes responsible for the recent dynamics in cod recruitment and outline directions for future research.

Winter habitat selection by a montane forest bird assemblage: the effects of solar radiation

2001 ◽  
Vol 79 (2) ◽  
pp. 279-284 ◽  
Author(s):  
Daniel L Huertas ◽  
José A Díaz
Keyword(s):  
Solar Radiation ◽  
Vegetation Structure ◽  
Prey Availability ◽  
Bird Species ◽  
Principal Component ◽  
Interspecific Variation ◽  
Montane Forest ◽  
Bird Abundance ◽  
Winter Habitat ◽  
Movement Rates

A relationship between sunlight and bird abundance in cold climates may seem intuitive and perhaps obvious. However, there is, surprisingly, little or no evidence to support it. We investigated the effects of solar radiation on the winter abundance of insectivorous birds inhabiting a Mediterranean montane forest with a high frequency of cold, cloudless days. We censused birds by ear in 20 different forest tracts in which we simultaneously quantified a number of variables related to the availability of solar radiation, vegetation structure, arthropod abundance, and altitude. All variables related to solar radiation were reduced to a single principal component that attained high scores for south-facing transects, where many tree trunks received direct sunlight for a long period daily. The abundance of all bird species was positively related to the scores of transects on this component after the effects of vegetation structure, altitude, and prey availability were controlled for. Solar radiation was the main predictor of overall abundance and species richness of bird assemblages. Body mass and diet (insectivorous vs. mixed) explained 94.6% of interspecific variation in the strength of the relationship between solar radiation and bird abundance. We hypothesize that selecting forest sectors with a higher availability of sunlit patches allows birds to improve their winter survival by reducing the metabolic costs of thermoregulation, decreasing movement rates, and (or) increasing the time spent motionless in safe locations.

Consequences of forest fragmentation on territory quality of male Ovenbirds breeding in western boreal forests

2002 ◽  
Vol 80 (11) ◽  
pp. 1841-1848 ◽  
Author(s):  
Daniel F Mazerolle ◽  
Keith A Hobson
Keyword(s):  
Forest Fragmentation ◽  
Vegetation Structure ◽  
Boreal Forests ◽  
Prey Availability ◽  
Forest Fragments ◽  
Territory Quality ◽  
Seiurus Aurocapillus ◽  
Prey Biomass ◽  
Prey Composition ◽  
Territory Selection

We evaluated the effects of forest fragmentation caused by agriculture on arthropod prey biomass and vegetation structure found in territories of male Ovenbirds (Seiurus aurocapillus) breeding in the southern boreal mixed woods of Saskatchewan, Canada. The objective of this study was to determine if previously documented differences in pairing success of male Ovenbirds in contiguous forests and forest fragments in our study area were associated with differences in arthropod prey biomass and vegetation structure between contiguous and fragmented forests. A secondary objective was to examine the correspondence between vegetation and arthropods to evaluate whether vegetation cues could be useful for birds attempting to predict future arthropod biomass during territory selection. Our results indicate that both vegetation structure and arthropod prey composition in Ovenbird territories differed between fragmented and contiguous forests, whereas total arthropod biomass did not. Furthermore, the correspondence of vegetation with arthropod prey composition and total prey biomass was weak, a result that questions the use of vegetation structure by male Ovenbirds for predicting future prey availability during territory selection. Overall, the current extent of forest fragmentation in our study area is not likely reducing pairing success of territorial male Ovenbirds by lowering the biomass of arthropod prey. However, landscape differences in vegetation structure could influence pairing success of male Ovenbirds in forest fragments by reducing suitable microhabitats for nesting or by increasing habitat suitability for nest predators and Brown-headed Cowbird (Molothrus ater) parasites.

scholarly journals Interactions among Land, Water, and Vegetation in Shoreline Arthropod Communities

2004 ◽  
Vol 3 (2) ◽  
Author(s):  
Randall Willoughby ◽  
Wendy Anderson
Keyword(s):  
Vegetation Structure ◽  
Prey Availability ◽  
Vegetation Type ◽  
Missouri River ◽  
Suitable Habitat ◽  
Arthropod Communities ◽  
Web Building ◽  
Emergent Insects ◽  
Rock Lake ◽  
Land Water

We investigated the distribution and abundance of terrestrial spiders as a function of their distance from a body of water and the structure of vegetation that would provide suitable habitat. We hypothesized that spiders would prefer to be located near the water to catch abundant aquatic emergent insects. In Montana along the Upper Missouri River, and in Missouri at various locations around Table Rock Lake, transect lines were run from the water’s edge to 25 meters inland. At five-meter intervals, in one square meter plots, the number of spiders, number of prey and type, and vegetation type and structure were recorded. In both Montana and Missouri, spider distribution was more strongly associated with available vegetation structure than with distance from shore. This suggests that, although prey availability may be important for predator distribution, suitable habitat is as strong or stronger a determinant for web building spiders.

scholarly journals Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure

2016 ◽  
Author(s):  
Elizabeth J Roberson ◽  
Michael J Chips ◽  
Walter P Carson ◽  
Thomas P Rooney
Keyword(s):  
Vegetation Structure ◽  
Prey Availability ◽  
Forest Disturbance ◽  
Geographic Region ◽  
Spider Webs ◽  
Spider Web ◽  
Food Web Interactions ◽  
Closed Canopy ◽  
Availability Index ◽  
Web Building

Indirect effects are a common feature of ecological systems, arising when one species affects interactions among two or more other species. We examined how browsing by white-tailed deer (Odocoileus virginianus) affected the abundance and composition of a web-building spider guild through their effects on the structure of the ground and shrub layers of northern hardwood forests. We examined paired plots consisting of deer-free and control plots in Pennsylvania and Wisconsin. We recorded the abundance of seven types of webs, each corresponding to a family of web-building spiders. We quantified vegetation structure and habitat suitability for the spiders by computing a web scaffold availability index (WSAI) at 0.5 m and 1.0 m above the ground. At Wisconsin sites, we recorded prey availability. Spider webs were twice as abundant in deer-free plots compared to control plots, while WSAI was 7-12 times greater in deer-free plots. Prey availability was also higher in deer-free plots. With the exception of funnel web-builders, all spider web types were significantly more abundant in deer-free plots. Both deer exclusion and the geographic region of plots were significant predictors of spider community structure. In closed canopy forests with high browsing pressure, the low density of tree saplings and shrubs provides few locations for web-building spiders to anchor webs. Recruitment of these spiders may become coupled with forest disturbance events that increase tree and shrub recruitment. By modifying habitat structure, deer indirectly modify arthropod food web interactions. As deer populations have increased in eastern North America over the past several decades, the effects of deer on web-building spiders may be widespread throughout the region.

scholarly journals Floral Resources Enhance Fecundity, but Not Flight Activity, in a Specialized Aphid Predator, Hippodamia convergens (Coleoptera: Coccinellidae)

2021 ◽  
Vol 9 ◽  
Author(s):  
Hannah E. Stowe ◽  
J. P. Michaud ◽  
Tania N. Kim
Keyword(s):  
Body Size ◽  
Reproductive Success ◽  
Prey Availability ◽  
Flight Activity ◽  
Flight Behavior ◽  
Floral Resources ◽  
Adult Survival ◽  
Adult Size ◽  
Hippodamia Convergens ◽  
Adult Diet

Adult aphid predators disperse across the landscape seasonally in search of prey aggregations that are patchily distributed and temporally variable. However, flight is energetically costly and consumes resources that could be invested in reproduction. Hippodamia convergens is an important aphid predator in North American cereal crops and other agricultural systems. Consumption of floral resources can enhance adult survival during periods of low prey availability and may improve reproductive success. We tested how an omnivorous adult diet containing floral resources (diluted honey and pulverized bee pollen) interacts with body size to influence reproduction and flight behavior compared to a prey-only diet. Two sizes of beetles were produced by controlling larval access to food—3 h daily access produced small beetles; ad libitum access produced large beetles with faster development. Reproductive performance was tracked for 18 days, and female flight activity was assayed via 3 h bouts of tethered flight. Diet composition and body size interacted to influence preoviposition period, with large females in prey-only treatments delaying oviposition the longest. The omnivorous adult diet improved 18-day fecundity relative to a prey-only diet, but egg fertility was unaffected. Adult size affected oviposition pattern, with small beetles laying smaller, but more numerous, clutches. Females flew up to 7 km in 6 h, but neither body size nor adult diet influenced flight distance, suggesting that all diet treatments generated energy reserves sufficient to power flights of short duration. However, pre-reproductive females flew > 60% further than they did post-reproduction, likely due to the energetic costs of oviposition. Thus, access to pollen and nectar increased reproductive success and altered oviposition patterns in H. convergens, indicating the importance of floral resources in the agricultural landscape to conservation of this predator and its biological control services.

scholarly journals Occupancy of avian foraging guilds in soybean fields and borders in Entre Ríos, Argentina: responses to vegetation structure and prey resources

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Andrea P. Goijman ◽  
Michael J. Conroy ◽  
Vanina D. Varni ◽  
Jeffrey J. Thompson ◽  
María Elena Zaccagnini
Keyword(s):  
Ecosystem Services ◽  
Vegetation Structure ◽  
Prey Availability ◽  
Wide Spectrum ◽  
Bird Species ◽  
Imperfect Detection ◽  
Native Trees ◽  
Foraging Guilds ◽  
Field Borders ◽  
Entre Rios

Abstract Background Reconciling agriculture and biodiversity conservation is a challenge given the growing demand for agricultural products. In recent decades, Argentina has witnessed agricultural expansion and intensification affecting biodiversity and associated ecosystem services. Within agroecosystems, the level of habitat quality is critical for birds, and may depend on vegetation structure, availability of invertebrate prey, and the use of pesticides. Although the relationship between vegetation structure and avian occurrence has been widely studied, to our knowledge, there are no studies that also incorporate prey availability throughout the cycle of soybean crops in Argentina. We estimated and predicted the effects of land cover and temporal variation on the occurrence of avian foraging guilds in Entre Ríos, Argentina, in order to guide management related to potential ecosystem services provided by birds. We also estimated temporal effects of vegetation structure and insecticides on the main arthropod orders consumed by birds to evaluate prey availability. Methods We conducted bird and arthropod surveys for 2 years along transects located in 20 randomly selected soybean fields (N = 60) and their adjacent borders (N = 78) throughout the crop growing season, in four seasons. We estimated avian occupancy, accounting for imperfect detection, and arthropod counts fitting generalized linear mixed models. Results The number of native trees in field borders positively influenced the occurrence of most bird species, mainly insectivores. Granivore foliage gleaners, also were positively affected by grass height. Salliers and aerial foragers were weakly affected by distance to forest and native trees. In general, the availability of invertebrates to birds was highest during the third season. Arthropod counts in borders were greater during the last three crop stages than during the pre-sowing period. Conclusions We found that with 10 to 15 native tree species in borders, coupled with a complex vegetation structure with shrubs and grasses, we could conserve a wide spectrum of insectivorous birds, and may contribute to the invertebrate pest control service. Vegetated field borders function as a refuge for arthropods, especially agriculturally beneficial taxa such as Hymenopterans. Finally, several groups of birds use the interior of the fields and could help control pests.

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