Inconsistent effects of landscape heterogeneity and land-use on animal diversity in an agricultural mosaic: a multi-scale and multi-taxon investigation

Context

The landscape heterogeneity hypothesis states that increased heterogeneity in agricultural landscapes will promote biodiversity. However, this hypothesis does not detail which components of landscape heterogeneity (compositional or configurational) most affect biodiversity and how these compare to the effects of surrounding agricultural land-use.

Objectives

Our objectives were to: (1) assess the influence of the components of structural landscape heterogeneity on taxonomic diversity; and (2) compare the effects of landscape heterogeneity to those of different types of agricultural land-use in the same landscape across different taxonomic groups.

Methods

We identified a priori independent gradients of compositional and configurational landscape heterogeneity within an agricultural mosaic of north-eastern Swaziland. We tested how bird, dung beetle, ant and meso-carnivore richness and diversity responded to compositional and configurational heterogeneity and agricultural land-use across five different spatial scales.

Results

Compositional heterogeneity best explained species richness in each taxonomic group. Bird and ant richness were both positively correlated with compositional heterogeneity, whilst dung beetle richness was negatively correlated. Commercial agriculture positively influenced bird species richness and ant diversity, but had a negative influence on dung beetle richness. There was no effect of either component of heterogeneity on the combined taxonomic diversity or richness at any spatial scale.

Conclusions

Our results suggest that increasing landscape compositional heterogeneity and limiting the negative effects of intensive commercial agriculture will foster diversity across a greater number of taxonomic groups in agricultural mosaics. This will require the implementation of different strategies across landscapes to balance the contrasting influences of compositional heterogeneity and land-use. Strategies that couple large patches of core habitat across broader scales with landscape structural heterogeneity at finer scales could best benefit biodiversity.

     

A regional analysis of total nitrogen in an agricultural landscape

Techniques for modeling spatial variability in the loss, gain, and storage of total nitrogen (N) in an agricultural landscape were developed utilizing a geographic information system (GIS) based on the Map Analysis Package (C.D. Tomlin, Yale University). The study area is a well-monitored portion (upper 114.9 km²) of the Little River Watershed, located near Tifton, Georgia, U.S.A. On the basis of measured N in the soil and vegetation, and the gains and losses of N by stream discharge, fertilizer, precipitation, N fixation, crop harvest, etc., it was possible to quantify and map source and sink regions of Total N, and to calculate a mass balance of N for an entire year. Results indicate massive flows of N, especially from anthropogenic sources. However, for the watershed as a whole, the N is virtually in balance with a small accretion occurring mostly in the riparian zones. Stream discharge of total N indicates that this landscape is well-buffered against excessive losses of N despite the large agricultural inputs.     

Movement behavior in response to landscape structure: the role of functional grain

Landscape structure can influence the fine-scale movement behavior of dispersing animals, which ultimately may influence ecological patterns and processes at broader scales. Functional grain refers to the finest scale at which an organism responds to spatial heterogeneity among patches and extends to the limits of its perceptual range. To determine the functional grain of a model insect, red flour beetle (Tribolium castaneum), we examined its movement behavior in response to experimental flour landscapes. Landscape structure was varied by manipulating habitat abundance (0%, 10%, 30%, and 100%) and grain size of patches (fine-2 × 2 cm, intermediate-5 × 5 cm, and coarse-10 × 10 cm) in 50 × 50 cm landscapes. Pathway metrics indicated that beetles used a similar proportion of all landscape types. Several pathway metrics indicated a graded response from the fine to the coarse grain landscape. Lacunarity analysis of beetle pathways indicated a non-linear change in space use between the fine and intermediate landscapes and the coarse-grained landscape. Beetles moved more slowly and tortuously (with many turns), and remained longer in both the overall landscape and individual patches, in fine-grained compared to coarse-grained landscapes. Our research demonstrates how detailed examination of movement pathways and measures of lacunarity can be useful in determining functional grain. Spatially explicit, organism-centered studies focusing on behavioral responses to different habitat configurations can serve as an important first step to identify behavioral rules of movement that may ultimately lead to more accurate predictions of space use in landscapes.     

How measures of agricultural landscape patterns are affected by crop rotation dynamics

Landscape Ecology - Landscape patterns have been measured as a fundamental part of landscape ecology, especially with increasing computational power and availability of landcover data. Among the...     

The response of elephants to the spatial heterogeneity of vegetation in a Southern African agricultural landscape

Based on the agricultural landscape of the Sebungwe in Zimbabwe, we investigated whether and how the spatial distribution of the African elephant (Loxodonta africana) responded to spatial heterogeneity of vegetation cover based on data of the early 1980s and early 1990s. We also investigated whether and how elephant distribution responded to changes in spatial heterogeneity between the early 1980s and early 1990s. Vegetation cover was estimated from a normalised difference vegetation index (NDVI). Spatial heterogeneity was estimated from a new approach based on the intensity (i.e., the maximum variance exhibited when a spatially distributed landscape property such as vegetation cover is measured with a successively increasing window size or scale) and dominant scale (i.e., the scale or window size at which the intensity is displayed). We used a variogram to quantify the dominant scale (i.e., range) and intensity (i.e., sill) of NDVI based congruent windows (i.e., 3.84 km × 3.84 km in a 61 km × 61 km landscape). The results indicated that elephants consistently responded to the dominant scale of spatial heterogeneity in a unimodal fashion with the peak elephant presence occurring in environments with dominant scales of spatial heterogeneity of around 457–734 m. Both the intensity and dominant scale of spatial heterogeneity predicted 65 and 68% of the variance in elephant presence in the early 1980s and in the early 1990s respectively. Also, changes in the intensity and dominant scale of spatial heterogeneity predicted 61% of the variance in the change in elephant distribution. The results imply that management decisions must take into consideration the influence of the levels of spatial heterogeneity on elephants in order to ensure elephant persistence in agricultural landscapes.     

Effects of interactive scale-dependent variables on beetle diversity patterns in a semi-arid agricultural landscape

Understanding species-diversity patterns in heterogeneous landscapes invites comprehensive research on how scale-dependent processes interact across scales. We used two common beetle families (Tenebrionidae, detrivores; Carabidae, predators) to conduct such a study in the heterogeneous semi-arid landscape of the Southern Judean Lowland (SJL) of Israel, currently undergoing intensive fragmentation. Beetles were censused in 25 different-sized patches (500–40,000 m²). We used Fisher’s α and non-parametric extrapolators to estimate species diversity from 11,125 individuals belonging to 56 species. Patch characteristics (plant species diversity and cover, soil cover and degree of stoniness) were measured by field transects. Spatial variables (patch size, shape, physiognomy and connectivity) and landscape characteristics were analyzed by GIS and remote-sensing applications. Both patch-scale and landscape-scale variables affected beetle species diversity. Path-analysis models showed that landscape-scale variables had the strongest effect on carabid diversity in all patches. The tenebrionids responded differently: both patch-scale and landscape-scale variables affected species diversity in small patches, while mainly patch-scale variables affected species diversity in large patches. Most of the paths affected species diversity both directly and indirectly, combining the effects of both patch-scale and landscape-scale variables. These results match the biology of the two beetle families: Tenebrionidae, the less mobile and more site-attached family, responded to the environment in a fine-grained manner, while the highly dispersed Carabidae responded to the environment in a coarse-grained manner. We suggest that understanding abiotic and biotic variable interactions across scales has important consequences for our knowledge of community structure and species diversity patterns at large spatial scales.     

Quantifying the agricultural landscape and assessing spatio-temporal patterns of precipitation and groundwater use

Quantitative agricultural landscape indices are useful to describe functional relationships among climatic conditions, groundwater dynamics, soil properties and agricultural land use for mathematical models. We applied methods of regression statistics, variance component estimation and a Geographical Information System (GIS) to construct indices describing crops and soils and to establish functional relationships among these variables. This paper describes the development of indices and the partitioning of the spatial and temporal variation in groundwater models using the data from Tulare County, California, which was selected as the study area. Indices of ground surface elevation, total crop water demand, soil water infiltration rate, and soil production index explain 91% of the variation in average spring groundwater level. After relating spatial patterns of groundwater use to indices of crop and soil properties, we found that mean groundwater use is positively related to total crop water demand and soil water infiltration rate while the variation in groundwater use was negatively correlated with the crop water demand and soil water infiltration rate and positively related to soil water holding capacity. The spatial variation in groundwater use was largely influenced by crops and soil types while the temporal variation was not. We also found that groundwater use increased exponentially with decreasing annual precipitation for most townships. Based on these associations, groundwater use in each township can be forecast from relative precipitation under current methods of agricultural production. Although groundwater table depth is strongly affected by topography, the statistically significant indices observed in the model clearly show that agricultural land use influences groundwater table depth. These simple relationships can be used by agronomists to make water management decisions and to design alternative cropping systems to sustain agricultural production during periods of surface water shortages.     

Additive partitioning of plant species diversity in an agricultural mosaic landscape

In this paper, we quantify the effects of habitat variability and habitat heterogeneity based on the partitioning of landscape species diversity into additive components and link them to patch-specific diversity. The approach is illustrated with a case study from central Switzerland, where we recorded the presence of vascular plant species in a stratified random sample of 1'280 quadrats of 1 m² within a total area of 0.23 km². We derived components of within- and between-community diversity at four scale levels (quadrat, patch, habitat type, and landscape) for three diversity measures (species richness, Shannon index, and Simpson diversity). The model implies that what we measure as within-community diversity at a higher scale level is the combined effect of heterogeneity at various lower levels. The results suggest that the proportions of the individual diversity components depend on the habitat type and on the chosen diversity aspect. One habitat type may be more diverse than another at patch level, but less diverse at the level of habitat type. Landscape composition apparently is a key factor for explaining landscape species richness, but affects evenness only little. Before we can test the effect of landscape structure on landscape species richness, several problems will have to be solved. These include the incorporation of neighbourhood effects, the unbiased estimation of species richness components, and the quantification of the contribution of a landscape element to landscape species richness.     

Movement of mud snails affects population dynamics,primary production and landscape heterogeneity in tidal flat ecosystems

Landscape Ecology - Animal movements influence the spatial heterogeneity of variously ecosystem processes. However, our understand of how movement in heterogeneous landscapes shapes ecological...     

Habitat factors related to wild rabbit conservation in an agricultural landscape

Populations of European wild rabbit (Oryctolagus cuniculus) have been decreasing since the 1950s. Changes in agricultural practices have been suggested as reasons for their decline in Mediterranean landscapes. We evaluated the environmental variables affecting rabbit distribution in a semiarid agricultural landscape of Northeastern Spain. Sampling was performed in 147 sites randomly distributed across Zaragoza province. At each site, data were recorded in five 100 m segments along a 1 km transect, following ecotones between crops and natural-vegetation areas. A rabbit abundance index was estimated from latrine count, pellet density and number of plots with pellets. In addition to environmental variables that have been shown to be related to rabbit abundance in other habitats, as climate, soil hardness and topography of the site, we measured landscape components related to agricultural use, such as structure of natural vegetation in remaining areas non-devoted to agricultural use and distances to different types of crops and to ecotone between crop and natural vegetation. Our results showed that rabbit abundance was positively correlated to yearly mean temperature, February and May mean rainfall, and negatively correlated to September and November mean rainfall, hardness of soil, and site topography. In relation to agricultural use, rabbit abundance was positively correlated to the scrub structure of natural-vegetation areas and negatively correlated to distance to edge between cultivated unirrigated cereal crops (wheat or barley) and yearly resting cereal crops. Rabbit abundance increased only when the edge between alternate cereal crops was less than 50 m from the ecotone between crops and natural vegetation.This revised version was published online in May 2005 with corrections to the Cover Date.     

Artificial light at night as a driver of urban colonization by an avian predator

Context

Urbanization and artificial light at night (ALAN) are major drivers of local biodiversity losses causing community alterations, disruption of predator-prey interactions, and ultimately, promotion of cascading effects. However, some species can colonize urban environments.

Objectives

We explore the role of ALAN as a driver of the colonization of urban environments by a nocturnal avian predator, the burrowing owl Athene cunicularia.

Methods

We studied in a suburban locality in La Pampa, Argentina: (1) prey availability with pitfall traps under streetlights and control sites; (2) diet by analyzing pellets; (3) space use by deploying GPS data-loggers to breeding owls; (4) nesting habitat selection by comparing environmental variables at nest and random locations; and (5) productivity by correlating environmental variables with the number of fledglings.

Results

First, streetlights altered the invertebrate availability, attracting them to illuminated areas. Second, the owl diet was more similar to the invertebrate taxa trapped at pitfall traps under streetlights than that in control traps. Third, owl space use was determined by streetlights. Owls spent more time around light sources, particularly during the nighttime. Fourth, the most important habitat feature influencing the nesting habitat selection was the distance to streetlight. Owls selected areas close to streetlights for nesting. Finally, productivity was not explained by any of our habitat variables.

Conclusions

We demonstrate that ALAN alters the availability of invertebrates and plays a role in the diet, space use, and occupation of urban burrowing owls. Streetlights increase foraging efficiency for owls due to the clumping of prey attracted to lights. This predator-prey relationship might be only supported in suburban environments where low urbanization levels let burrowing owls nest in bare ground areas, and invertebrates are attracted to ALAN from surrounding wilder areas.

     

Resource patch array use by two squirrel species in an agricultural landscape

Eastern grey squirrels (Sciurus carolinensis) and North American red squirrels (Tamiasciurus hudsonicus) were studied among wooded patches within an agricultural mosaic. Fifteen sites south of Ottawa, Canada, with differing landscape and local features were censused using tracking boards placed in a woods or wooded fencerow. Regression analyses of landscape compositional and physiognomic variables within a 1-km radius isolated the best predictors of grey and red squirrel abundance and activity. Grey squirrels were found in both small woods and fencerows in farm landscapes but were not found in large woods. A polynomial regression of wooded patch size explained 79% of the variance in grey squirrel abundance. Grey squirrel activity was correlated with the percent cover of soybeans in the landscape. Red squirrels were found in fencerows, small and large woods; activity was correlated with the percent cover of both woods and corn crop in the surrounding landscape. These results indicate that distributions of both species are influenced by multiple landscape elements, but that grey squirrels may rely on fragmented agricultural landscapes whereas red squirrels make more use of both native woodland and altered landscapes.     

Spatially explicit correlates of plant functional traits inform landscape patterns of resource quality

Landscape Ecology - Spatially explicit correlates of foliar elemental, stoichiometric, and phytochemical (ESP) traits represent links to landscape patterns of resource quality. We investigate...     

Making the connection: combining habitat suitability and landscape connectivity to understand species distribution in an agricultural landscape

Landscape Ecology - The current biodiversity crisis has intensified the need to predict species responses to landscape modification and has renewed attention on the fundamental question of what...     

Response of generalist and specialist insect herbivores to landscape spatial structure

The purpose of this study was to investigate the effect ofchanges in landscape pattern on generalist and specialistinsects. We did this by comparing the species richness andabundance of generalist and specialist herbivorous insects inalfalfa (Medicago sativa, L.) fields on 26 agriculturallandscapes that differed in spatial structure. The insects werefrom the families Curculionidae (Coleoptera), weevils, andCicadellidae (Auchennorhyncha), leafhoppers.We hypothesized that: (1) generalist richness and abundancewould be highest in landscapes with high diversity(Shannon-Wiener); (2) specialist richness and abundance would behighest in landscapes with (i) high percent cover alfalfa and(ii) low mean inter-patch distance. We tested for these effectsafter controlling for the patch-level effects of field size,field age, frequency of disturbance and vegetation texture.The important findings of the study are: (1) generalist richness andabundance increased with increasing landscape diversity and (2)isolation (percent cover alfalfa in the landscape and/or meaninter-patch distance) does not affect specialist insects. Theseresults are significant because they indicate that bothgeneralist and specialist insects may move over much largerdistances than previously thought. This is one of the firststudies to demonstrate a large scale effect of spatial structureon insects across a broad range of landscapes.     

Spatial and semantic dimensions of landscape heterogeneity

This paper addresses the challenge of measuring spatial heterogeneity in categorical map data. Spatial heterogeneity is a complex notion that involves both spatial variability and attribute variability, and metrics to capture this are a product of their developers’ simplifying assumptions about both spatial and attribute dimensions. We argue that the predominantly binary treatment of categorical data is frequently an unnecessary oversimplification that can be replaced by ordered measures based on semantic similarity evaluations. We develop a typology of autocorrelation metrics for categorical data that identifies a critical gap: existing measures are limited in their ability to capture variability of both spatial and attribute dimensions simultaneously. We demonstrate an approach to formally characterize the semantic similarity between pairs of categorical data classes as a continuous numeric variable. A series of experiments on synthetic and actual land cover data contrasts the information content provided by metrics representative of all portions of the typology: the recently proposed semantic variogram, the indicator variogram, the contagion index, and the edge contrast index. Experimental results suggest that the typology captures essential qualities of metric information richness. Among our findings is that the commonly used contagion index is directly correlated with Moran’s I for 2-class maps but it fails to distinguish between negatively and positively autocorrelated patterns. We identify the semantic variogram as the only metric that can simultaneously detect both spatial and semantic attribute aspects of categorical autocorrelation. The semantic variogram is also relatively robust to attribute scale changes and therefore less sensitive to class aggregation than the other metrics.     

Effects of land use on population presence and genetic structure of an amphibian in an agricultural landscape

Context

Species distributions are a function of an individual’s ability to disperse to and colonize habitat patches. These processes depend upon landscape configuration and composition.

Objectives

Using Blanchard’s cricket frogs (Acris blanchardi), we assessed which land cover types were predictive of (1) presence at three spatial scales (pond-shed, 500 and 2500 m) and (2) genetic structure. We predicted that forested, urban, and road land covers would negatively affect cricket frogs. We also predicted that agricultural, field, and aquatic land covers would positively affect cricket frogs.

Methods

We surveyed for cricket frogs at 28 sites in southwestern Ohio, USA to determine presence across different habitats and analyze genetic structure among populations. For our first objective, we examined if land use (crop, field, forest, and urban habitat) and landscape features (ponds, streams, and roads) explained presence; for our second objective, we assessed whether these land cover types explained genetic distance between populations.

Results

Land cover did not have a strong influence on cricket frog presence. However, multiple competing models suggested effects of roads, streams, and land use. We found genetic structuring: populations were grouped into five major clusters and nine finer-scale clusters. Highways were predictive of increased genetic distance.

Conclusions

By combining a focal-patch study with landscape genetics, our study suggests that major roads and waterways are key features affecting species distributions in agricultural landscapes. We demonstrate that cricket frogs may respond to landscape features at larger spatial scales, and that presence and movement may be affected by different environmental factors.

     

Urban heat islands and landscape heterogeneity: linking spatiotemporal variations in surface temperatures to land-cover and socioeconomic patterns

The urban heat island (UHI) phenomenon is a common environmental problem in urban landscapes which affects both climatic and ecological processes. Here we examined the diurnal and seasonal characteristics of the Surface UHI in relation to land-cover properties in the Phoenix metropolitan region, located in the northern Sonoran desert, Arizona, USA. Surface temperature patterns derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer for two day-night pairs of imagery from the summer (June) and the autumn (October) seasons were analyzed. Although the urban core was generally warmer than the rest of the area (especially at night), no consistent trends were found along the urbanization gradient. October daytime data showed that most of the urbanized area acted as a heat sink. Temperature patterns also revealed intra-urban temperature differences that were as large as, or even larger than, urban–rural differences. Regression analyses confirmed the important role of vegetation (daytime) and pavements (nighttime) in explaining spatio-temporal variation of surface temperatures. While these variables appear to be the main drivers of surface temperatures, their effects on surface temperatures are mediated considerably by humans as suggested by the high correlation between daytime temperatures and median family income. At night, however, the neighborhood socio-economic status was a much less controlling factor of surface temperatures. Finally, this study utilized geographically weighted regression which accounts for spatially varying relationships, and as such it is a more appropriate analytical framework for conducting research involving multiple spatial data layers with autocorrelated structures.     

Influence of within-field and landscape factors on aphid predator populations in wheat

The influence of prey density, within-field vegetation, and the composition and patchiness of the surrounding landscape on the abundance of insect predators of cereal aphids was studied in wheat fields in eastern South Dakota, USA. Cereal aphids, aphid predators, and within-field vegetation were sampled in 104 fields over a three year period (1988–1990). The composition and patchiness of the landscape surrounding each field were determined from high altitude aerial photographs. Five landscape variables, aggregated at three spatial scales ranging from 2.6 km² to 581 km², were measured from aerial photographs. Regression models incorporating within-field and landscape variables accounted for 27–49% of the variance in aphid predator abundance in wheat fields. Aphid predator species richness and species diversity were also related to within-field and landscape variables. Some predators were strongly influenced by variability in the composition and patchiness of the landscape surrounding a field at a particular spatial scale while others responded to variability at all scales. Overall, predator abundance, species richness, and species diversity increased with increasing vegetational diversity in wheat fields and with increasing amounts of non-cultivated lands and increasing patchiness in the surrounding landscape.     

浅析景墙在景观环境中的功能属性

通过挖掘景墙在景观环境中的功能,阐述了相关场所对景墙功能的要求,以及相应功能的表达方式,最后对景墙的应用提出了不足和展望。