Seeking parsimony in landscape metrics

Agricultural Landscape Composition Linked with Acoustic Measures of Avian Diversity

Measuring, monitoring, and managing biodiversity across agricultural regions depends on methods that can combine high-resolution mapping of landscape patterns with local biodiversity observations. This study explores the potential to monitor biodiversity in agricultural landscapes by linking high-resolution remote sensing with passive acoustic monitoring. Land cover maps produced using a small unmanned aerial system (UAS) and PlanetScope (PS) satellite imagery were used to investigate relationships between landscape patterns and an acoustically derived biodiversity index (vocalizing bird species richness) across 12 agricultural sample locations equipped with acoustic recorders in Iowa, USA during the 2018 growing season. Statistical assessment revealed a significant direct association between vocalizing bird richness and percent noncrop vegetation cover. High spatial resolution (1 m) UAS mapping produced stronger statistical associations than PS-based maps (3 m) for landscape composition metrics. Landscape configuration metrics (Shannon’s diversity index, contagion, perimeter-area-ratio, and circumscribing circle index) were either cross-correlated with composition metrics or unusable owing to complete landscape homogeneity in some agricultural landscape samples. This study shows that high resolution mapping of noncrop vegetation cover can be linked with acoustic monitoring of unique bird vocalizations to provide a useful indicator of biodiversity in agricultural landscapes.

Home range size, vegetation density, and season influences prey use by coyotes (Canis latrans)

To ensure reproductive success, Canis species establish contiguous mosaics of territories in suitable habitats to partition space and defend limiting resources. Consequently, Canis species can exert strong effects on prey populations locally because of their year-round maintenance of territories. We assessed prey use by coyotes (Canis latrans) by sampling scats from within known territories in southeastern Alabama and the Savannah River area of Georgia and South Carolina. We accounted for the size and habitat composition of coyote home ranges to investigate the influence of space use, vegetation density, and habitat type on coyote diets. Coyote use of prey was influenced by a combination of mean monthly temperature, home range size, vegetation density, and hardwood forests. For example, coyote use of adult white-tailed deer (Odocoileus virginianus) was associated with cooler months and smaller home ranges, whereas use of rabbits (Sylvilagus spp.) was associated with cooler months, larger home ranges, and less vegetation density. Coyotes in our study relied primarily on nutritionally superior mammalian prey and supplemented their diet with fruit when available, as their use of mammalian prey did not appreciably decrease with increasing use of fruit. We suggest that differential use of prey by coyotes is influenced by habitat heterogeneity within their home ranges, and prey-switching behaviors may stabilize local interactions between coyotes and their food resources to permit stable year-round territories. Given that habitat composition affects coyote prey use, future studies should also incorporate effects of habitat composition on coyote distribution and abundance to further identify coyote influences on prey communities.

Effects of shade cocoa plantation on artificial fruit consumption by birds in two contrasting landscapes in Southern Bahia, Brazil

To investigate the influence of forests and agroforestry systems on fruit consumption by birds, we studied two landscapes, one covered predominantly with forests and the other dominated by traditional shade cocoa plantations. In each landscape, we sampled three forest fragments and three shade cocoa plantations. We placed 15 artificial fruits in 25, 1–2-m-tall shrubs spaced every 50 m and evaluated the detection and consumption of fruits after 72 h. We used hemispherical photographs positioned above each fruit station to evaluate canopy openness. We found a statistically significant difference in fruit consumption between landscapes, which means that more fruits were detected and consumed in the forest-dominated landscape. However, forests and shade cocoa plantations within each landscape exhibited similar fruit consumption. Canopy openness was similar between the landscapes, however, the cocoa plantations exhibited greater canopy openness than forests. The results of this study reinforce the importance of the presence of forests in the agricultural landscape. Thus, to evaluate the capacity of agroforest to protect species and maintain ecological interactions it is also necessary to consider the landscape context.

Habitat selection and ranges of tolerance: how do species differ beyond critical thresholds?

Sensitivity to habitat fragmentation often has been examined in terms of thresholds in landscape composition at which a species is likely to occur. Observed thresholds often have been low or absent, however, leaving much unexplained about habitat selection beyond initial thresholds of occurrence, even for species with strong habitat preferences. We examined responses to varying amounts of tree cover, a widely influential measure of habitat loss, for 40 woodland bird species in a mixed woodland/grassland landscape in eastern North Dakota, USA. We used LOESS smoothing to describe incidence for each species at three scales: within 200, 400, and 1200 m around sample locations. For the 200-m scale, we also calculated the most-preferred range of tree cover (within which at least half of observations were predicted to occur) for each species. Only 10 of 40 species had occurrence thresholds greater than about 10% tree cover. After initial occurrence, species showed three general patterns: some increased monotonically with tree cover; some increased up to an asymptote; some peaked at intermediate amounts of tree cover and then declined. These patterns approximate selection for interior woodlands and for edge-rich environments, but incidence plots provide greater detail in landscape-scale selection than do those categories. For most species, patterns persisted at larger scales, but for some, larger scales had distinctly different patterns than local scales. Preferred ranges of tree cover varied from <20% tree cover (common grackle, Quiscalus quiscula) to >60% (veery, Catharus fuscescens). We conclude that incidence patterns provide more information on habitat selection than do threshold measures for most species: in particular, they differentiate species preferring concentrated woodlands from those preferring mixed landscapes, and they show contrasting degrees of selectiveness. [Correction added on 16 October 2012, after first online publication: the Abstract section has been reworded].