Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which make... more Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which makes it a complex response with ecological implications. In plants with long-term belowground storage, allocation of biomass to inaccessible parts belowground in response to folivory is a well-recognized tolerance mechanism. In temperate regions, spring growth from buried rootstock is common among winter deciduous plants and is often followed by regrowth after defoli-ation, both of which draws resources from the stored reserves. We developed a mathematical model to analyze this tolerance response in a winter deciduous plant with long-term below-ground biomass when it is defoliated by a specialist insect folivore. The model explores how three closely associated traits—(1) belowground biomass allocation to roots, (2) spring utilization of stored reserves, and (3) post-defoliation regrowth capacity—modulate the persistence and dynamics of the plant and herbivore populations. Model results show that allocation to belowground storage is not only a critical component of tolerance but also influences the herbivore population dynamics in ways that depend on how and when plant biomass is allocated and used. Low belowground biomass allocation and high storage utilization combined with poor photosynthetic growth caused extirpation of the plant population by the defoliating insects. Stable coexistence of the plant at low biomass along with its specialist insect required a moderate amount of post-herbivory belowground allocation. High values of belowground biomass allocation, storage utilization, and photosynthetic growth resulted in sustained cycles of the herbivore and plant populations. Interestingly, utilization of stored reserves had conflicting influence on above and below-ground biomass, and strongly affected herbivore population dynamics. Our model thus highlights the complexity of tolerance response when it involves multiple traits and mechanisms as evinced by winter deciduous plants. We close by discussing the implications of our findings for the contributions of defoliating insects to biocontrol programs.
Background/Question/Methods: Between the two recognized categories of plant defense strategies, r... more Background/Question/Methods: Between the two recognized categories of plant defense strategies, resistance and tolerance; tolerance is critical in determining the impact of defoliation by insect herbivores. The significance of tolerance as a defense strategy is further augmented in the context of biocontrol management of invasive plants as it is typically based on insect herbivory. Moreover, invasive plants with long-term belowground biomass are plants that can tolerate high amounts of aboveground defoliation or biomass loss. We developed a theoretical model for an invasive plant with long-term stored biomass and seasonal growth and its specialist insect herbivore using three state variables: aboveground biomass, belowground biomass and herbivore population density. The theoretical model analyses how three closely associated traits—(i) belowground biomass allocation to roots, (ii) spring utilization of stored reserves, and (iii) post-herbivory regrowth capacity—modulate the persiste...
ABSTRACT Understand How to Analyze and Interpret Information in Ecological Point Patterns Althoug... more ABSTRACT Understand How to Analyze and Interpret Information in Ecological Point Patterns Although numerous statistical methods for analyzing spatial point patterns have been available for several decades, they haven’t been extensively applied in an ecological context. Addressing this gap, Handbook of Spatial Point-Pattern Analysis in Ecology shows how the techniques of point-pattern analysis are useful for tackling ecological problems. Within an ecological framework, the book guides readers through a variety of methods for different data types and aids in the interpretation of the results obtained by point-pattern analysis. Ideal for empirical ecologists who want to avoid advanced theoretical literature, the book covers statistical techniques for analyzing and interpreting the information contained in ecological patterns. It presents methods used to extract information hidden in spatial point-pattern data that may point to the underlying processes. The authors focus on point processes and null models that have proven their immediate utility for broad ecological applications, such as cluster processes. Along with the techniques, the handbook provides a comprehensive selection of real-world examples. Most of the examples are analyzed using Programita, a continuously updated software package based on the authors’ many years of teaching and collaborative research in ecological point-pattern analysis. Programita is tailored to meet the needs of real-world applications in ecology. The software and a manual are available online.
Background/Question/Methods Larrea tridentata (creosote bush) is the dominant perennial shrub thr... more Background/Question/Methods Larrea tridentata (creosote bush) is the dominant perennial shrub throughout most of the arid regions of the southwestern US. Associated with Larrea are “fertility islands” with high amounts of nutrients located under shrub canopies that decrease in amount away from the shrubs. Native annuals tend to grow predominantly under shrub canopies. However, some exotic species, which have invaded the SW American deserts, tend to grow in the open, producing more litter between shrubs. As a result, wildfires have become more frequent and intense with the increase in fuel load connecting shrubs. Little is known about the real impact of wildfires in the spatial distribution of Larrea shrublands and potential implications for the arid plant community. In this research we evaluated how wildfires may affect the spatial distribution of the Larrea shrubs within the Sonoran and Mojave deserts. In each desert, we studied a region that was subjected to a wildfire in 2005 and...
Background/Question/Methods Fire risk is increasing in ecoregions historically not prone to fire,... more Background/Question/Methods Fire risk is increasing in ecoregions historically not prone to fire, such as creosote shrublands of the desert Southwest. It is hypothesized that one of the primary drivers producing novel fire regimes in these shrublands is the increasing abundance of exotic annuals. Schismus sp. is particularly important as it can spread between shrubs, whereas native annuals, at least in the Mojave, tend to be restricted to growing under shrubs. The increase in exotic annuals potentially provides a fuel bed for fire spread that did not previously exist. We studied these issues utilizing an experimental approach in two sites, one in the Mojave and one in the Sonora. This included an exploration of changing water availability, soil disturbance and seed input on recruitment and growth of annuals at different distances from shrubs. Using the results, we explore the implications for fire spread using a modeling approach. The model has three vegetation layers: (i) intershru...
ABSTRACT The distribution of invasive plants across a landscape is largely governed by disturbanc... more ABSTRACT The distribution of invasive plants across a landscape is largely governed by disturbance invoking anthropogenic land-use practices and propagule pressure. However, spatial variability associated with anthropogenic disturbances and propagule pressure is seldom used to develop distribution models of invasive plants. This study makes use of large-scale survey data to develop a spatially explicit predictive model for the invasive wetland plant—purple loosestrife. Using loosestrife presence data and land use land cover information, we first predicted loosestrife occurrences in two types of wetland habitat, namely herbaceous wetlands and open-water edges, with a series of logistic regression models that incorporated surrounding land-use at three different neighborhood scales. The best-fitting surrounding land-use model was then combined with three different distance constraint models that simulated propagule pressure. Loosestrife occurrence as a function of surrounding land-use showed best fit at a neighborhood radius of 400 m. Predictions made from the surrounding land-use model at the 400 m scale were fairly accurate and loosestrife invasion of wetland locations were correlated with the proportion of anthropogenic land-use conditions. Inclusion of an autocovariate simulating propagule pressure improved model fit and performance significantly. Model findings suggest that spatially explicit incorporation of surrounding land-use yields an ecologically realistic projection of invasion risk wherein disturbance prone habitat edges tend to be more invasible. Combining this prediction with location specific estimates of propagule pressure further reduces uncertainty by spatially constraining areas of high invasion risk. Our approach is applicable to other invasive plants since it is based on two key drivers of plant invasion: disturbance and propagule-pressure.
ABSTRACT Background/Question/Methods The vegetation of the Sonoran and Mojave deserts is characte... more ABSTRACT Background/Question/Methods The vegetation of the Sonoran and Mojave deserts is characterized by shrublands dominated by Larrea tridentata(creosote bush) and other smaller co-dominant species. These shrubs create fertility islands that harbor native and invasive annual plants, providing considerable amounts of fuel for fires in the dry season. The spatial patterns of shrubs and fertility islands they create can have major effects on spread of wildfire. We assessed the ability to infer information about shrub distribution from orthorectified aerial imagery (at 24-50cm resolution). In both deserts we studied regions of approximately 1 hectare, including areas affected by wildfires in 2005. We used ImageJ software to determine the location and size of shrubs visible in the aerial image and compared these data to data gathered in the field using a GPS device (accuracy 30-50cm) and hand measurements of canopy size. We assessed the ability of the aerial image to accurately determine shrub size using linear regression, and the spatial pattern of the shrub population using the pair correlation function and the mark correlation function. We also determined if the images could be used to determine the locations of burned shrubs and to distinguish Larrea from Ambrosiain the Mojave. Results/Conclusions In the Sonoran, we were able to use the 24cm imagery to determine the shrub size in the field (AreaField=0.84 + 1.06*AreaImage, R2=0.67), and locate shrubs over 0.04 m2 in area within 1m of the GPS locations. In the burned area, many shrubs that we classified as dead or as a stump were discernible on the 24cm imagery. In the Mojave, where Larrea and Ambrosia are co-dominant, we used the mean pixel intensity to distinguish between species. The minimum shrub visible at 50cm resolution is 0.24 m2, which excluded about 1% of the Larrea population and 22% of the Ambrosia population. These images were able to estimate shrub size, but with more bias than in the Sonoran (AreaField=0.58 + 0.48*AreaImage, R2=0.74). The choice of threshold pixel intensity value to segment shrub objects from the background introduced a tradeoff between accuracy for count and location-based statistics (number of shrubs and univariate point pattern analysis) and accuracy for area-based statistics (area estimation and marked point pattern analysis). Use of aerial imagery to obtain information on shrub spatial patterns can reveal how wildfires affect the geometry and spatial pattern of perennial shrubs and the resulting distribution of fuel for wildfires.
Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which make... more Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which makes it a complex response with ecological implications. In plants with long-term belowground storage, allocation of biomass to inaccessible parts belowground in response to folivory is a well-recognized tolerance mechanism. In temperate regions, spring growth from buried rootstock is common among winter deciduous plants and is often followed by regrowth after defoli-ation, both of which draws resources from the stored reserves. We developed a mathematical model to analyze this tolerance response in a winter deciduous plant with long-term below-ground biomass when it is defoliated by a specialist insect folivore. The model explores how three closely associated traits—(1) belowground biomass allocation to roots, (2) spring utilization of stored reserves, and (3) post-defoliation regrowth capacity—modulate the persistence and dynamics of the plant and herbivore populations. Model results show that allocation to belowground storage is not only a critical component of tolerance but also influences the herbivore population dynamics in ways that depend on how and when plant biomass is allocated and used. Low belowground biomass allocation and high storage utilization combined with poor photosynthetic growth caused extirpation of the plant population by the defoliating insects. Stable coexistence of the plant at low biomass along with its specialist insect required a moderate amount of post-herbivory belowground allocation. High values of belowground biomass allocation, storage utilization, and photosynthetic growth resulted in sustained cycles of the herbivore and plant populations. Interestingly, utilization of stored reserves had conflicting influence on above and below-ground biomass, and strongly affected herbivore population dynamics. Our model thus highlights the complexity of tolerance response when it involves multiple traits and mechanisms as evinced by winter deciduous plants. We close by discussing the implications of our findings for the contributions of defoliating insects to biocontrol programs.
Background/Question/Methods: Between the two recognized categories of plant defense strategies, r... more Background/Question/Methods: Between the two recognized categories of plant defense strategies, resistance and tolerance; tolerance is critical in determining the impact of defoliation by insect herbivores. The significance of tolerance as a defense strategy is further augmented in the context of biocontrol management of invasive plants as it is typically based on insect herbivory. Moreover, invasive plants with long-term belowground biomass are plants that can tolerate high amounts of aboveground defoliation or biomass loss. We developed a theoretical model for an invasive plant with long-term stored biomass and seasonal growth and its specialist insect herbivore using three state variables: aboveground biomass, belowground biomass and herbivore population density. The theoretical model analyses how three closely associated traits—(i) belowground biomass allocation to roots, (ii) spring utilization of stored reserves, and (iii) post-herbivory regrowth capacity—modulate the persiste...
ABSTRACT Understand How to Analyze and Interpret Information in Ecological Point Patterns Althoug... more ABSTRACT Understand How to Analyze and Interpret Information in Ecological Point Patterns Although numerous statistical methods for analyzing spatial point patterns have been available for several decades, they haven’t been extensively applied in an ecological context. Addressing this gap, Handbook of Spatial Point-Pattern Analysis in Ecology shows how the techniques of point-pattern analysis are useful for tackling ecological problems. Within an ecological framework, the book guides readers through a variety of methods for different data types and aids in the interpretation of the results obtained by point-pattern analysis. Ideal for empirical ecologists who want to avoid advanced theoretical literature, the book covers statistical techniques for analyzing and interpreting the information contained in ecological patterns. It presents methods used to extract information hidden in spatial point-pattern data that may point to the underlying processes. The authors focus on point processes and null models that have proven their immediate utility for broad ecological applications, such as cluster processes. Along with the techniques, the handbook provides a comprehensive selection of real-world examples. Most of the examples are analyzed using Programita, a continuously updated software package based on the authors’ many years of teaching and collaborative research in ecological point-pattern analysis. Programita is tailored to meet the needs of real-world applications in ecology. The software and a manual are available online.
Background/Question/Methods Larrea tridentata (creosote bush) is the dominant perennial shrub thr... more Background/Question/Methods Larrea tridentata (creosote bush) is the dominant perennial shrub throughout most of the arid regions of the southwestern US. Associated with Larrea are “fertility islands” with high amounts of nutrients located under shrub canopies that decrease in amount away from the shrubs. Native annuals tend to grow predominantly under shrub canopies. However, some exotic species, which have invaded the SW American deserts, tend to grow in the open, producing more litter between shrubs. As a result, wildfires have become more frequent and intense with the increase in fuel load connecting shrubs. Little is known about the real impact of wildfires in the spatial distribution of Larrea shrublands and potential implications for the arid plant community. In this research we evaluated how wildfires may affect the spatial distribution of the Larrea shrubs within the Sonoran and Mojave deserts. In each desert, we studied a region that was subjected to a wildfire in 2005 and...
Background/Question/Methods Fire risk is increasing in ecoregions historically not prone to fire,... more Background/Question/Methods Fire risk is increasing in ecoregions historically not prone to fire, such as creosote shrublands of the desert Southwest. It is hypothesized that one of the primary drivers producing novel fire regimes in these shrublands is the increasing abundance of exotic annuals. Schismus sp. is particularly important as it can spread between shrubs, whereas native annuals, at least in the Mojave, tend to be restricted to growing under shrubs. The increase in exotic annuals potentially provides a fuel bed for fire spread that did not previously exist. We studied these issues utilizing an experimental approach in two sites, one in the Mojave and one in the Sonora. This included an exploration of changing water availability, soil disturbance and seed input on recruitment and growth of annuals at different distances from shrubs. Using the results, we explore the implications for fire spread using a modeling approach. The model has three vegetation layers: (i) intershru...
ABSTRACT The distribution of invasive plants across a landscape is largely governed by disturbanc... more ABSTRACT The distribution of invasive plants across a landscape is largely governed by disturbance invoking anthropogenic land-use practices and propagule pressure. However, spatial variability associated with anthropogenic disturbances and propagule pressure is seldom used to develop distribution models of invasive plants. This study makes use of large-scale survey data to develop a spatially explicit predictive model for the invasive wetland plant—purple loosestrife. Using loosestrife presence data and land use land cover information, we first predicted loosestrife occurrences in two types of wetland habitat, namely herbaceous wetlands and open-water edges, with a series of logistic regression models that incorporated surrounding land-use at three different neighborhood scales. The best-fitting surrounding land-use model was then combined with three different distance constraint models that simulated propagule pressure. Loosestrife occurrence as a function of surrounding land-use showed best fit at a neighborhood radius of 400 m. Predictions made from the surrounding land-use model at the 400 m scale were fairly accurate and loosestrife invasion of wetland locations were correlated with the proportion of anthropogenic land-use conditions. Inclusion of an autocovariate simulating propagule pressure improved model fit and performance significantly. Model findings suggest that spatially explicit incorporation of surrounding land-use yields an ecologically realistic projection of invasion risk wherein disturbance prone habitat edges tend to be more invasible. Combining this prediction with location specific estimates of propagule pressure further reduces uncertainty by spatially constraining areas of high invasion risk. Our approach is applicable to other invasive plants since it is based on two key drivers of plant invasion: disturbance and propagule-pressure.
ABSTRACT Background/Question/Methods The vegetation of the Sonoran and Mojave deserts is characte... more ABSTRACT Background/Question/Methods The vegetation of the Sonoran and Mojave deserts is characterized by shrublands dominated by Larrea tridentata(creosote bush) and other smaller co-dominant species. These shrubs create fertility islands that harbor native and invasive annual plants, providing considerable amounts of fuel for fires in the dry season. The spatial patterns of shrubs and fertility islands they create can have major effects on spread of wildfire. We assessed the ability to infer information about shrub distribution from orthorectified aerial imagery (at 24-50cm resolution). In both deserts we studied regions of approximately 1 hectare, including areas affected by wildfires in 2005. We used ImageJ software to determine the location and size of shrubs visible in the aerial image and compared these data to data gathered in the field using a GPS device (accuracy 30-50cm) and hand measurements of canopy size. We assessed the ability of the aerial image to accurately determine shrub size using linear regression, and the spatial pattern of the shrub population using the pair correlation function and the mark correlation function. We also determined if the images could be used to determine the locations of burned shrubs and to distinguish Larrea from Ambrosiain the Mojave. Results/Conclusions In the Sonoran, we were able to use the 24cm imagery to determine the shrub size in the field (AreaField=0.84 + 1.06*AreaImage, R2=0.67), and locate shrubs over 0.04 m2 in area within 1m of the GPS locations. In the burned area, many shrubs that we classified as dead or as a stump were discernible on the 24cm imagery. In the Mojave, where Larrea and Ambrosia are co-dominant, we used the mean pixel intensity to distinguish between species. The minimum shrub visible at 50cm resolution is 0.24 m2, which excluded about 1% of the Larrea population and 22% of the Ambrosia population. These images were able to estimate shrub size, but with more bias than in the Sonoran (AreaField=0.58 + 0.48*AreaImage, R2=0.74). The choice of threshold pixel intensity value to segment shrub objects from the background introduced a tradeoff between accuracy for count and location-based statistics (number of shrubs and univariate point pattern analysis) and accuracy for area-based statistics (area estimation and marked point pattern analysis). Use of aerial imagery to obtain information on shrub spatial patterns can reveal how wildfires affect the geometry and spatial pattern of perennial shrubs and the resulting distribution of fuel for wildfires.
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Papers by Kirk Moloney