Joint effects of habitat configuration and temporal stochasticity on population dynamics

Habitat configuration and temporal stochasticity in the environment are recognized as important drivers of population structure, yet few studies have examined the combined influence of these factors. We developed a spatially explicit simulation model to investigate how stochasticity in survival and reproduction influenced population dynamics on landscapes that differed in habitat configuration. Landscapes ranged from completely contiguous to highly fragmented, and simulated populations varied in mean survival probability (0.2, 0.4, 0.8) and dispersal capacity (1, 3, or 5 cells). Overall, habitat configuration had a large effect on populations, accounting for >80% of the variation in population size when mean survival and dispersal capacity were held constant. Stochasticity in survival and reproduction were much less influential, accounting for <1–14% of the variation in population size, but exacerbated the negative effects of habitat fragmentation by increasing the number of local extinctions in isolated patches. Stochasticity interacted strongly with both mean survival probability and habitat configuration. For example, survival stochasticity reduced population size when survival probability was high and habitat was fragmented, but had little effect on population size under other conditions. Reproductive stochasticity reduced population size irrespective of mean survival and habitat configuration, but had the largest effect when survival probability was intermediate and habitat was well connected. Stochasticity also enhanced the variability of population size in most cases. Contrary to expectations, increasing dispersal capacity did not increase population persistence, because the probability of finding suitable habitat within the dispersal neighborhood declined more for the same level of dispersal capacity when fragmentation was high compared to when it was low. These findings suggest that greater environmental variability, as might arise due to climate change, is likely to compound population losses due to habitat fragmentation and may directly reduce population size if reproductive output is compromised. It may also increase variability in population size.     

Surface metrics: an alternative to patch metrics for the quantification of landscape structure

Modern landscape ecology is based on the patch mosaic paradigm, in which landscapes are conceptualized and analyzed as mosaics of discrete patches. While this model has been widely successful, there are many situations where it is more meaningful to model landscape structure based on continuous rather than discrete spatial heterogeneity. The growing field of surface metrology offers a variety of surface metrics for quantifying landscape gradients, yet these metrics are largely unknown and/or unused by landscape ecologists. In this paper, we describe a suite of surface metrics with potential for landscape ecological application. We assessed the redundancy among metrics and sought to find groups of similarly behaved metrics by examining metric performance across 264 sample landscapes in western Turkey. For comparative purposes and to evaluate the robustness of the observed patterns, we examined 16 different patch mosaic models and 18 different landscape gradient models of landscape structure. Surface metrics were highly redundant, but less so than patch metrics, and consistently aggregated into four cohesive clusters of similarly behaved metrics representing surface roughness, shape of the surface height distribution, and angular and radial surface texture. While the surface roughness metrics have strong analogs among the patch metrics, the other surface components are largely unique to landscape gradients. We contend that the surface properties we identified are nearly universal and have potential to offer new insights into landscape pattern–process relationships. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparing landscape scale vegetation dynamics following recent disturbance in climatically similar sites in California and the Mediterranean basin

A long line of inquiry on the notion of ecological convergence has compared ecosystem structure and function between areas that are evolutionarily unrelated but under the same climate regime. Much of this literature has focused on quantifying the degree to which animal morphology or plant physiognomy is alike between disjunct areas. An important property of ecosystems is their behavior following disturbance. Yet, this aspect of ecosystems has not been investigated in a comparative study of convergence. If different ecosystems are under similar environmental controls, then one would predict that the rates and patterns of response to disturbance would also be similar. The objective of this study is to compare landscape dynamics following disturbance using spatiotemporal models to quantify vegetation change in Mediterranean ecosystems found in California and Israel. We model the process of tree and shrub regeneration at the landscape scale in two similar study sites in Israel (Mount Meron) and California (Hasting Nature Reserve). During the periods studied (1964-1992 for Israel and 1971-1995 for California), average annual change in tree cover was 5 times larger in Israel than in California. Based on multiple regression models, differences were found in the relative importance of specific variables predicting vegetation change. In Hastings (California), initial tree cover accounted for most of the explained variability in 1995 tree cover (partial R² = 0.71), while in Meron (Israel), grazing type and intensity, topography indices, and initial vegetation each accounted for about a third of the explained variability. These findings support the notion that traits such as regeneration pattern and rate, both at the individual level and at the landscape level, were largely affected by the human land use history of the region.     

Population dynamics and habitat connectivity affecting the spatial spread of populations – a simulation study

In this paper we show how the spatialconfiguration of habitat quality affects the spatial spread of apopulation in a heterogeneous environment. Our main result is thatfor species with limited dispersal ability and a landscape withisolated habitats, stepping stone patches of habitat greatlyincrease the ability of species to disperse. Our results showthat increasing reproductive rate first enables and thenaccelerates spatial spread, whereas increasing the connectivity has aremarkable effect only in case of low reproductive rates. Theimportance of landscape structure varied according to thedemographic characteristics of the population. To show this wepresent a spatially explicit habitat model taking into accountpopulation dynamics and habitat connectivity. The population dynamicsare based on a matrix projection model and are calculated on eachcell of a regular lattice. The parameters of the Leslie matrix dependon habitat suitability as well as density. Dispersal between adjacentcells takes place either unrestricted or with higher probability inthe direction of a higher habitat quality (restricted dispersal).Connectivity is maintained by corridors and stepping stones ofoptimal habitat quality in our fragmented model landscape containinga mosaic of different habitat suitabilities. The cellular automatonmodel serves as a basis for investigating different combinations ofparameter values and spatial arrangements of cells with high and lowquality.This revised version was published online in May 2005 with corrections to the Cover Date.     

桂林北部柑橘园橘小实蝇田间消长动态研究

连续4年对桂林北部全州县柑橘园的橘小实蝇进行田间消长动态监测,并根据当地气象资料分析气象因素与橘小实蝇发生动态的关系。结果表明,橘小实蝇在当地于5月下旬至7月中旬开始活动,9月上旬至11月下旬之间会出现2次活动高峰期,12月上旬以后活动停止或减弱;气温和日照时数是影响当地橘小实蝇活动动态的主要气象因子。     

Modeling the Impact of Climate and Vegetation on Fire Regimes in Mountain Landscapes

Assessing the long-term dynamics of mountain landscapes that are influenced by large-scale natural and anthropogenic disturbances and a changing climate is a complex subject. In this study, a landscape-level ecological model was modified to this end. We describe the structure and evaluation of the fire sub-model of the new landscape model LandClim, which was designed to simulate climate–fire–vegetation dynamics. We applied the model to an extended elevational gradient in the Colorado Front Range to test its ability to simulate vegetation composition and the strongly varying fire regime along the gradient. The simulated sequence of forest types along the gradient corresponded to the one observed, and the location of ecotones lay within the range of observed values. The model captured the range of observed fire rotations and reproduced realistic fire size distributions. Although the results are subject to considerable uncertainty, we conclude that LandClim can be used to explore the relative differences of fire regimes between strongly different climatic conditions.     

Effect of historic landscape change on the genetic structure of the bush-cricket Metrioptera roeseli

This study investigates the impact of past and present landscape structure on the current genetic structure of the bush-cricket Metrioptera roeseli (Orthoptera, Tettigoniidae) in a rural landscape in Germany. Assuming that land-use types, such as grassland, arable land and forest, as well as linear structures, mainly roads, differentially affect the connectivity of the bush-cricket's habitat and therefore migration and gene flow, we correlated landscape parameters between sampling locations as derived from GIS-maps with genetic similarities between individual bush-crickets as estimated by RAPD-PCR. Fifty bush-crickets were sampled with distances between sampling locations varying between 15 m and 2 km. Corresponding landscape configurations were recorded in 8 years between 1945 and 1998. Landscape configuration 50 years ago appeared to have influenced the present genetic structure of the bush-cricket (R ² = 0.18). Crossing roads and land use other than grassland along the transect between sampling locations tended to decrease genetic similarity, whereas grassland and parallel roads tended to increase genetic similarity between bush-crickets. Following shifts in land use during 1953–1973 the correlation between landscape and present genetic structure decreased gradually. Our study suggests that it needs time for the landscape to build a visible effect on the genetic structure of the bush-cricket population, and that this effect cannot be detected if the landscape changes faster than the genetic structure responds to it.     

Multi-scale effects of habitat loss and fragmentation on lesser prairie-chicken populations of the US Southern Great Plains

Large-scale patterns of land use and fragmentation have been associatedwith the decline of many imperiled wildlife populations. Lesserprairie-chickens(Tympanuchus pallidicinctus) are restricted to thesouthernGreat Plains of North America, and their population and range have declined by> 90% over the past 100 years. Our objective was to examine scale-dependentrelationships between landscape structure and change and long-term populationtrends for lesser prairie-chicken populations in the southern Great Plains. Weused a geographic information system (GIS) to quantify landscape composition,pattern and change at multiple scales (extents) for fragmented agriculturallandscapes surrounding 10 lesser prairie-chicken leks. Trend analysis oflong-term population data was used to classify each population and landscape(declined, sustained). We analyzed metrics of landscape structure and changeusing a repeated measures analysis of variance to determine significant effects( = 0.10) between declining and sustained landscapes across multiplescales. Four metrics of landscape structure and change (landscape change index,percent cropland, increases in tree-dominated cover types, and changes in edgedensity) contained significant interactions between population status andscale,indicating different scaling effects on landscapes with declining and stablepopulations. Any single spatial scale that was evaluated would not have givencomplete results of the influences of landscape structure and change on lesserprairie-chicken populations. The smallest spatial scales (452, 905, and 1,810ha) predicted that changes in edge density and largest patch sizewere the only important variables, while large-scale analysis (7,238ha) suggested that the amount of cropland, increase in trees(mostly Juniperus virginiana), and general landscapechanges were most important. Changes in landscape structure over the pastseveral decades had stronger relationships with dynamics of lesserprairie-chicken populations than current landscape structure. Observed changessuggest that these local populations may be appropriately viewed from ametapopulation perspective and future conservation efforts should evaluateeffects of fragmentation on dispersal, colonization, and extinction patterns.This revised version was published online in May 2005 with corrections to the Cover Date.     

Historical influence of man on the riparian dynamics of a fluvial landscape

Man's influence, over the last three centuries, has gradually influenced the dynamics of forest cover along the valley of the Garonne, a seventh order river in Southern France. The vegetation cover of the floodplain depends on topographical levels which govern the frequency and duration of submergence during flooding. Along the valley, forest patches vary from a continuous ribbon of riparian wood along the river to a mosaic of groves towards the upland terraces. In the floodplain, the forest dynamics are influenced by floods, appear to be reversible, and are subject to dominant allogenic processes. On the contrary, forest dynamics on the terraces, which are not influenced by floods, are irreversible and subjected to dominant autogenic processes. Since the end of the 17th century, the structure of riparian woods has been modified by navigation and agriculture leading to a fragmentation of forest cover in the floodplain. Modern agriculture and urbanization have accentuated these tendencies by modifying the hydrologic regime of the river. These historical changes result in a fragmentation of forest cover and a substitution of species in the riparian zone, the forest dynamics being still reversible in the floodplain.     

Assessing the potential impacts of climate change on the alpine habitat suitability of Japanese stone pine (Pinus pumila)

To assess the potential distribution of Pinus pumila, a dominant species of the Japanese alpine zone, and areas of its habitats vulnerable to global warming, we predicted potential habitats under the current climate and two climate change scenarios (RCM20 and MIROC) for 2081–2100 using the classification tree (CT) model. The presence/absence records of P. pumila were extracted from the Phytosociological Relevé Database as response variables, and five climatic variables (warmth index, WI; minimum temperature for the coldest month, TMC; summer precipitation, PRS; maximum snow water equivalent, MSW; winter rainfall, WR) were used as predictor variables. Prediction accuracy of the CT evaluated by ROC analysis showed an AUC value of 0.97, being categorized as “excellent”. We designated Third Mesh cells with an occurrence probability of 0.01 or greater as potential habitats and further divided them into suitable and marginal habitats based on the optimum threshold probability value (0.06) in ROC analysis. Deviance weighted scores revealed that WI was the largest contributing factor followed by MSW. Changes in habitat types from the current climate to the two scenarios were depicted within an observed distribution (Hayashi’s distribution data). The area of suitable habitats under the current climate decreased to 25.0% and to 14.7% under the RCM20 and MIROC scenarios, respectively. Suitable habitats were predicted to remain on high mountains of two unconnected regions, central Honshu and Hokkaido, while they were predicted to vanish in Tohoku and southwestern Hokkaido. Thus P. pumila populations in these regions are vulnerable to climate change.     

Effects of corridor width and presence on the population dynamics of the meadow vole (Microtus pennsylvanicus)

We tested the effects of increased landscape corridor width and corridor presence on the population dynamics and home range use of the meadow vole (Microtus pennsylvanicus) within a small-scale fragmented landscape. Our objective was to observe how populations behaved in patchy landscapes where the animals home range exceeded or equaled patch size. We used a small-scale replicated experiment consisting of three sets of two patches each, unconnected or interconnected by 1-m or 5-m wide-corridors, established in an old-field community (S.W. Ohio). Control (0-m) treatments supported significantly lower vole densities than either corridor treatment. Females were the dominant resident sex establishing smaller home ranges (<150m²) than males (>450m²). Significantly more male voles dispersed between patches with corridors than between patches without corridors. However, no difference was observed regarding the number of male voles dispersing between patches connected by corridors when compared to the number dispersing across treatments. Dispersal between connected patches was restricted to corridors based on tracking tube data. Corridor presence was more important than corridor width regarding the movement of male voles within their home range.     

Neighbourhood landscape effect on population kinetics of the fossorial water vole (<Emphasis Type="Italic">Arvicola terrestris scherman</Emphasis>)

This paper addresses the issue of whether landscape structure affects A. terrestris population kinetics on a neighbourhood spatial scale, and if so, at what spatial scale is that effect at its maximum. We investigated how the growth of A. terrestris populations is influenced by the landscape context of parcels used for hay production in the French Jura Mountains. Five landscape metrics (relative area of grassland, mean patch area of grassland, patch density of grassland, woodland patch density in grassland, grassland–woodland edge density) were computed over an increasing radius around each parcel (max. 3 km). Redundancy analysis showed that the extent, rate and early onset of A. terrestris population growth were favoured in open grassland areas. Landscape effects on A. terrestris populations as determined by the five metrics are scale-dependent: mean patch area of grassland, patch density of grassland and woodland patch density in grassland had an impact on a grassland parcel within a neighbourhood radius of about 800 m, while relative area of grassland and grassland–woodland edge density had an impact within a neighbourhood radius of about 400 m. Those findings corroborate earlier hypotheses about a multifactorial regulation of A. terrestris populations and a spatial hierarchy of regulating factors. They have potential implications in terms of landscape management and small mammal pest control.     

Research article Canopy dynamics and human caused disturbance on a semi-arid landscape in the Rocky Mountains,USA

Invasion of grasslands by woody plants has been identified as a key indicator of changes in ecosystem structure and function in arid and semi-arid rangelands throughout the world. We investigated changes in the balance between woody and herbaceous components of a semi-arid landscape in western Colorado (USA) using historical aerial photography. Aerial photographs from 1937, 1965–67, and 1994 were sampled at matched locations within overlapping photographs. We modeled change in spatial pattern and heterogeneity across the entire landscape and found a small, net decrease in woody canopy cover; however means disguised normal distributions of change that demonstrated offsetting increases and decreases. We described a region of widespread canopy decline within piñon-juniper forests between 2300 and 2600 m (7500–8500 feet) and a region of predominant increase at lower elevations, between 1800 and 2250 m (5900–7400 feet). It remains unclear whether this shift was driven by climate or by human-caused or natural disturbance. Mean conifer cover decreased within coniferous forests, which counteracted a trend of increased conifer cover in mixed forests, savanna-like woodlands, and the shrub steppe. Disturbance had a significant interaction with cover change in several communities, including forests, savanna and shrublands. Anthropogenic disturbances counteracted successional trends toward canopy closure more than wildfires, but this did not entirely explain observed canopy decline. The natural dynamics in this region also caused diverse changes rather than a simple progression towards increased forest cover. Importantly, temporal change in vegetation varied spatially across the landscape illustrating the importance of landscape level, spatially explicit analyses in characterizing temporal dynamics.     

Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability

While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners. The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns for forest sustainability.     

Landscape patterns and agriculture: modelling the long-term effects of human practices on Pinus sylvestris spatial dynamics (Causse Mejean, France)

This paper focuses on understanding human impact on landscape. Both ecological and human practices are analysed as interacting processes. An agent-based model integrating biological and historical knowledge is used to analyse the pattern of Scots Pine encroachment in a French Mediterranean upland. In the STIPA model, pine trees are autonomous agents and a cellular automaton simulates land-use. We test the effects of shifting cultivation on tree establishment at the landscape scale. This allows us to understand how agropastoral practices patterned this area from the 17th to 19th century: simulations show the importance of shifting cultivation in limiting woodland progression. Fallow duration linked to environmental heterogeneity is a significant factor for explaining pine dynamics and landscape patterning at the scale of the study region. We put this result in perspective with current rangeland management policies that often consider grazing as the most relevant tool for open landscape maintenance. Our results also show the importance of taking into account time-scale effects when linking landscape patterns to agricultural systems.     

Assessing the impacts of urbanization-associated green space on urban land surface temperature: A case study of Dalian,China

Taking Dalian City as the study area, the spatial distribution of urban green space and land surface temperature (LST), as well as their evolution in 1999, 2007 and 2013, were obtained through remote sensing (RS) interpretation and inversion. Landsat ETM and SPOT data were used for this purpose. By combining the temperature and vegetation index models (TVX), the effects of urban green space reduction on the thermal environment during city development were evaluated. The results show the following. (1) During 1999–2013, 88.1 km² of urban green space was converted to other land uses, accounting for a 29.4% reduction in urban green space in the study area. (2) During the study period, the LST in this area increased by +8.455 K. The evolution of the regional thermal landscape can be characterized by increases in the LST, greater complexity of the thermal landscape structure, increase and aggregation of high-temperature areas, and reduction and fragmentation of low-temperature areas. (3) During the process of urbanization, urban green space with low land-surface temperature was converted to other land use types with high land-surface temperature. When development occurred at the price of urban green space, negative effects on the regional thermal environment were observed.     

Evaluating effects of low quality habitats on regional population growth in <Emphasis Type="Italic">Peromyscus leucopus</Emphasis>: Insights from field-parameterized spatial matrix models

Due to complex population dynamics and source–sink metapopulation processes, animal fitness sometimes varies across landscapes in ways that cannot be deduced from simple density patterns. In this study, we examine spatial patterns in fitness using a combination of intensive field-based analyses of demography and migration and spatial matrix models of white-footed mouse (Peromyscus leucopus) population dynamics. We interpret asymptotic population growth rates from these spatial models as fitness-based measures of habitat-quality and use elasticity analysis to further explore model behavior and the roles of migration. In addition, we compare population growth rates at the spatial scale of single habitats and the landscape-level scale at which these habitats are assembled. To this end, we employ emerging techniques in multi-scale estimation of demography and movement and recently described vec-permutation methods for spatial matrix notation and analysis. Our findings indicate that the loss of low quality habitats or reductions in movement from these habitats into higher quality areas could negatively affect landscape-level population fitness.     

Simulated effects of increasing atmospheric CO2 and changing climate on the successional characteristics of Alpine forest ecosystems

Possible effects of changing climate and increasing CO₂ on forest stand development were simulated using a forest succession model of the JABOWA/FORET type. The model was previously tested for its ability to generate plausible community patterns for Alpine forest sites ranging from 220 m to 2000 m a.s.l., and from xeric to mesic soil moisture conditions. Each model run covers a period of 1000 yrs and is based on the averaged successional characteristics of 50 forest plots with an individual size of 1/12 ha. These small forest patches serve as basic units to model establishment, growth, and death of individual trees. The simulated CO₂ scenario assumes linear climate change as atmospheric CO₂ concentration increases from 310 l/l to 620 l/l and finally to 1340 l/l. Direct effects of increasing CO₂ on tree growth were modeled using tree-ring and growth chamber data. The simulation experiment proved to be a useful tool for evaluating possible vegetation changes that might occur under CO₂-induced warming. On xeric sites from the colline to the high montane belt, the simulated climate change causes drastic soil water losses due to elevated evapotranspiration rates. This translates into a significant biomass decrease and even to a loss of forest on xeric low-elevation sites. Biomass gains can be reported from mesic to intermediate sites between 600 and 2000 m a.s.l. Increasing CO₂ and warming alters the species composition of the simulated communities considerably. In today's montane and subalpine belt an invasion of deciduous tree species can be expected. They outcompete most conifers which in turn may migrate to today's alpine belt. Some of these changes occur as early as 40 yrs after climate begins to change. This corresponds to a mean annual warming of 1.5°C compared with today's mean temperatures.     

Effect of matrix habitat on the spread of flea beetle introductions for biological control of leafy spurge

Matrix habitats are known to influence the movement patterns of a variety of species but it is less well known whether these effects have strong implications for spatial population dynamics, including the spread of biological introductions. Using a spatially explicit simulation model parameterized with empirical data, we examine how grass and shrub matrix habitats, each offering different resistance to dispersal, influence the spread and impact of a biocontrol agent, Aphthona lacertosa, on the invasive weed, leafy spurge. Model predictions indicate that differential responses to matrix habitat have little effect on the agent’s spread over the study landscape and this is supported by statistical models fit to observed A. lacertosa incidence on the same landscape. Subsequent experimentation with the simulation model suggested that A. lacertosa colonization rates were largely unaffected by increases in amount of the more restrictive shrub matrix. However, simulations of an hypothetical species with greater overall dispersal ability but reduced dispersal rate through shrub matrix showed that colonization rates were noticeably reduced when the percentage of shrub matrix on the landscape approached 50%. Combined these results suggest that some tailoring of release strategies may be required to accommodate the unique dispersal capabilities of different biocontrol agents on particular release landscapes, but for A. lacertosa there appears to be little effect of matrix habitat structure on rates of spread.