Seed terminal velocity, wind turbulence and demography drive the spread of an invasive tree in an analytical model

Little is known about the relative importance of mechanistic drivers of plant spread, particularly when long-distance dispersal (LDD) events occur. Most methods to date approach LDD phenomenologically, and all mechanistic models, with one exception, have been implemented through simulation. Furthermore, the few recent mechanistically derived spread models have examined the relative role of different dispersal parameters using simulations, and a formal analytical approach has not yet been implemented. Here we incorporate an analytical mechanistic wind dispersal model (WALD) into a demographic matrix model within an analytical integrodifference equation spread model. We carry out analytical perturbation analysis on the combined model to determine the relative effects of dispersal and demographic traits and wind statistics on the spread of an invasive tree. Models are parameterized using data collected in situ and tested using independent data on historical spread. Predicted spread rates and direction match well the two historical phases of observed spread. Seed terminal velocity has the greatest potential influence on spread rate, and three wind properties (turbulence coefficient, mean horizontal wind speed, and standard deviation of vertical wind speed) are also important. Fecundity has marginal importance for spread rate, but juvenile survival and establishment are consistently important. This coupled empirical/theoretical framework enables prediction of plant spread rate and direction using fundamental dispersal and demographic parameters and identifies the traits and environmental conditions that facilitate spread. The development of an analytical perturbation analysis for a mechanistic spread model will enable multispecies comparative studies to be easily implemented in the future

Demography and Management of the Invasive Plant Species Hypericum perforatum. II. Construction and Use of an Individual-Based Model to Predict Population Dynamics and the Effects of Management Strategies

1. Hypericum perforatum , St John's wort, is an invasive weed of natural and agro-ecosystems in south-eastern Australia. In previous work we used a long-term data set to determine which plant traits and environmental factors influence population growth and persistence in this species. These results were then used to parameterize an individual-based model of the population dynamics of H. perforatum , and this model was used to make predictions about what control strategies will be most effective for populations in open and shaded sites. 2. The model was constructed using multi-level, mixed-effects statistical models of growth, survival, fecundity and damage, incorporating intrinsic plant variables, environmental variables, herbivory and spatial and temporal stochasticity. 3. We found that populations in shaded and open sites had different dynamics and responses to control strategies. Shaded populations took longer to reach infestation densities and were less affected by herbivory and reductions in survival than open populations. Open populations increased faster in response to increases in rainfall, but this was not so for shaded populations. 4. We used sensitivity testing and management simulations to predict that the most successful control strategies will involve a reduction in vegetative size in both open and shaded sites. Reductions in flowering stem size and survival in shaded and open sites, respectively, are predicted to be the next most successful strategies. Dry conditions in the austral autumn/winter adversely affect populations in both open and shaded sites. 5. Synthesis and applications . These models have enabled us to rank management strategies based on quantitative analysis of their potential effects on population size. This is an important tool not only for ecologists concerned with control of invasive species but for conservation biologists trying to understand the factors limiting a rare or endangered species

Demography and Management of the Invasive Plant Species Hypericum perforatum. I. Using Multi-Level Mixed-Effects Models For Characterizing Growth, Survival and Fecundity in a Long-Term Data Set

1. Hypericum perforatum , St John's wort, is an invasive perennial herb that is especially problematic on waste ground, roadsides, pastures and open woodland in south-eastern Australia. We use detailed data from a long-term observational study to develop quantitative models of the factors affecting growth, survival and fecundity of H. perforatum individuals. 2. Multi-level or hierarchical mixed-effects statistical models are used to analyse how environmental and intrinsic plant variables affect growth and reproduction within a complex nested spatial and temporal context. These techniques are relatively underused in ecology, despite the prevalence of multi-level and repeated-measures data generated from ecological studies. 3. We found that plant size (rosette or flowering stems) was strongly correlated with all life stages studied (growth, probability of flowering, asexual reproduction, survival and fruit production). Environmental variables such as herbivory, ground cover and rainfall had significant effects on several life stages. 4. Significant spatial variation at the quadrat level was found in the probability of flowering, flowering stem growth and fruit production models; variation at all other spatial levels in all models was non-significant. Yearly temporal variation was significant in all models where multi-year data were available. 5. Plants in shaded habitats were smaller but had higher survival probabilities than plants in open habitats. They are therefore likely to have slightly different population dynamics. 6. Synthesis and applications. Analysis of these models for H. perforatum has provided insights into which plant traits and environmental factors determine how populations increase and persist in exotic ecosystems, enabling population management strategies to be most effectively targeted. Spatially and temporally correlated data are often collected in long-term ecological studies and multi-level models are a way in which we can fully exploit the wealth of data available. Without these tools data are either underexploited or crucial assumptions of independence on which many statistics are based are contravene

Offspring size plasticity in response to intraspecific competition: An adaptive maternal effect across life-history stages

When provisioning offspring, mothers balance the benefits of producing a few large, fitter offspring with the costs of decreased fecundity. The optimal balance between offspring size and fecundity depends on the environment. Theory predicts that larger offspring have advantages in adverse conditions, but in favorable conditions size is less important. Thus, if environmental quality varies, selection should favor mothers that adaptively allocate resources in response to local conditions to maximize maternal fitness. In the bryozoan Bugula neritina, we show that the intensity of intraspecific competition dramatically changes the offspring size/performance relationship in the field. In benign or extremely competitive environments, offspring size is less important, but at intermediate levels of competition, colonies from larger larvae have higher performance than colonies from smaller larvae. We predicted mothers should produce larger offspring when intermediate competition is likely and tested these expectations in the field by manipulating the density of brood colonies. Our findings matched expectations: mothers produced larger larvae at high densities and smaller larvae at low densities. In addition, mothers from high‐density environments produced larvae that have higher dispersal potential, which may enable offspring to escape crowded environments. It appears mothers can adaptively adjust offspring size to maximize maternal fitness, altering the offspring phenotype across multiple life‐history stages

Modelling Integrated Weed Management of an Invasive Shrub in Tropical Australia

1. Most invasive plant species are not well controlled and where biocontrol programs are in place only one third are fully successful. Integrated weed management (IWM) emphasises the use of several complementary control measures. Choosing which combinations will yield control and how biocontrol fits within the strategy requires detailed knowledge of the dynamics of the target and its ecosystem. 2. We used models of increasing complexity to determine which parameters affect site occupancy of an invasive shrub, Mimosa pigra L. in tropical Australia. Two introduced biocontrol agents have spatial effects on both plant fecundity and the probability of recolonisation after senescence. We incorporated biocontrol effects into IWM models with disturbance, mechanical control, herbicide and fire. The models were parameterised from experimental and field data. 3. Models indicate that the reduction in fecundity is not the most important impact of biocontrol; rather it is through defoliation at the edges of stands allowing grasses to out-compete M. pigra seedlings. We demonstrate that biocontrol alone is only successful at low disturbance and seedling survival and even then, current biocontrol agents would take decades to reduce a stand t

The 2020 general election: a gender analysis

The February 2020 general election will be remembered as the “change” election, when the two dominant parties of Irish politics, Fianna Fáil and Fine Gael, trailed behind Sinn Féin in voters' preferences for the first time. However, for the gender balance of Irish politics, much remained unchanged. While the number of women elected to Dáil Éireann increased by one, this marginal growth since the 2016 general election was deemed a disappointment by analysts and advocates alike. A review of candidacy reveals that Fianna Fáil and Fine Gael lag behind other parties in terms of the proportion of women selected and rely on the 'add-on' route to shore up their female candidacy base. The success rates of female candidates were markedly lower than those of their male counterparts in the Labour party, Greens, Fianna Fáil and Fine Gael. However, the election was a good outing for women in the Social Democrats and Sinn Féin, and especially for Mary Lou McDonald, who became the first woman to lead a party to top-spot in an Irish general election. The legislative gender quota continued to play an integral role in ensuring a critical mass of women were selected to contest the general election. In many respects, 2020 was a consolidation election for the gender quota as it fits-in and integrates into party candidate selection processes. Yet, with just 22.5% of the seats in Dáil Éireann occupied by women, the legislative gender quota should be viewed as the start rather than the culmination of efforts to support women's candidacy and election

Patterns of introduced species interactions affect multiple aspects of network structure in plant-pollinator communities

Species introductions have the potential to affect the functionality and stability of ecological communities, but because little is known about how introduced species form novel interactions, these impacts are difficult to predict. We quantified the impacts of species introductions on species interaction networks using five different model scenarios of how a novel species might form plant–pollinator interactions. The network structure was based on experimental manipulations on a community of plants and pollinators and shows that the community was more diverse, ordered, and compartmentalized, but less complex when an invasive plant generalist was present. Our models of species introductions reliably predicted several aspects of novel network structure in the field study. We found that introduced species that become incorporated into the community as generalists (both in the number and frequency of their interactions) have a much larger impact on the structure of plant–pollinator communities than introduced species that integrate into the community with few interactions. Average degree is strongly affected by the number of interactions the novel species forms and whether it competes for interactions, whereas connectance is affected by whether the novel species competes for interactions or adds new interaction partners. The number and size of compartments in the network change only when the novel species adds new interaction partners, while modularity and nestedness respond most to the number of interactions formed by the novel species. We provide a new approach for understanding the impacts of introduced and invasive species on plant–pollinator communities and demonstrate that it is critical to evaluate multiple structural characters simultaneously, as large changes in the fundamental structure of the community may be disguised

Dispersal capacity predicts both population genetic structure and species richness in reef fishes

Dispersal is a fundamental species characteristic that should directly affect both rates of gene flow among spatially distributed populations and opportunities for speciation. Yet no single trait associated with dispersal has been demonstrated to affect both micro- and macroevolutionary patterns of diversity across a diverse biological assemblage. Here, we examine patterns of genetic differentiation and species richness in reef fishes, an assemblage of over 7,000 species comprising approximately one-third of the extant bony fishes and over one-tenth of living vertebrates. In reef fishes, dispersal occurs primarily during a planktonic larval stage. There are two major reproductive and parental investment syndromes among reef fishes, and the differences between them have implications for dispersal: (1) benthic guarding fishes lay negatively buoyant eggs, typically guarded by the male parent, and from these eggs hatch large, strongly swimming larvae; in contrast, (2) pelagic spawning fishes release small floating eggs directly into the water column, which drift unprotected before small weakly swimming larvae hatch. Using phylogenetic comparative methods, we show that benthic guarders have significantly greater population structure than pelagic spawners and additionally that taxonomic families of benthic guarders are more species rich than families of pelagic spawners. Our findings provide a compelling case for the continuity between micro- and macroevolutionary processes of biological diversification and underscore the importance of dispersalrelated traits in influencing the mode and tempo of evolution

Measuring the shape of mortality across animals and plants: Alternatives to H entropy metrics reveal hidden type IV survivorship curves and associations with parental care at macro-ecological scales

Publication history: Accepted - 25 April 2023; Published - 17 May 2023.The shape of mortality, or how mortality is spread across an organism's life course, is fundamental to a range of biological processes, with attempts to quantify it rooted in ecology, evolution, and demography. One approach to quantify the distribution of mortality over an organism's life is the use of entropy metrics whose values are interpreted within the classical framework of survivorship curves ranging from type I distributions, with mortality concentrated in late life stages, to type III survivorship curves associated with high early stage mortality. However, entropy metrics were originally developed using restricted taxonomic groups and the behavior of entropy metrics over larger scales of variation may make them unsuitable for wider-ranging contemporary comparative studies. Here, we revisit the classic survivorship framework and, using a combination of simulations and comparative analysis of demography data spanning the animal and plant kingdoms, we show that commonly used entropy metrics cannot distinguish between the most extreme survivorship curves, which in turn can mask important macroecological patterns. We show how using H entropy masks a macroecological pattern of how parental care is associated with type I and type II species and for macroecological studies recommend the use of metrics, such as measures of area under the curve. Using frameworks and metrics that capture the full range of variation of survivorship curves will aid in our understanding of the links between the shape of mortality, population dynamics, and life history traits.Irish Research Council. Grant Number: COALESCE/2021/117 Irish Research Council postdoctoral fellowship scheme. Grant Number: GOIPD/2016/324 Science Foundation Ireland. Grant Number: 15/ERCD/280