Ben L. Phillips

A tale as old as time: early intervention has lower costs and higher probability of eradication success. ”Early” has been long engrained in invasion biology theory, but what constitutes ”early” remains vaguely defined. We argue that a critical transition between early and late intervention occurs when the spatial extent of the invasion becomes sufficiently large that we can no longer apply management effort to all parts of the population, and a more complex management strategy is required for successful eradication. The ”critical area” proposed here is defined by three factors: growth rate of the species; budget available for the management campaign; and effectiveness of surveillance and control technology. We derive a simple formula for the critical area and explore its effectiveness as a heuristic, using simulated invasions. Results from simulations in 2-Dimension show that starting intervention before the critical point has a 100% success; starting intervention at the critical point has a 78% success rate; and starting intervention after the critical point, has less than 1% success rate. We also examine how this heuristic might be used to guide decision making around the quantum of investment and optimal strategy to achieve eradication.

The impact of an invasive species is strongly influenced by the extent of its invaded range. Predicting the potential distribution of an invader is thus critical for informing decisions around surveillance, containment, and eradication. Such predictions ideally would come from a mechanistic species distribution model. These models directly describe how aspects of the environment affect organismal fitness, and may also provide insight into population dynamics, such as rates of population growth and spread. Here, we develop a temperature-dependent stage-structured population dynamic model for a globally significant invader, the polyphagous shot-hole borer (PSHB, Euwallacea fornicatus ). We use this model to predict the beetle's potential growth rate across its invaded range. Invasive PSHB causes serious damage to urban and agricultural trees, and so the continued expansion of its global distribution is a major concern. We synthesise previous studies to parameterise the model, yielding estimates of population growth as a function of daily temperatures within a host tree. We ran the model over one year using daily climate data across regions with invasive PSHB populations: South Africa, California, Israel and Australia. Our potential distribution maps indicate that PSHB currently occupies the most climatically suitable parts of California and Israel, but is yet to invade the most suitable regions in Australia and South Africa. The model shows the species is capable of very high population growth: in already-invaded locations, the average daily growth rate had an upper bound of ~ 0.05 (equivalent to population doubling in 14 days). Growth predictions were sensitive to the parameter for adult female mortality during between-host dispersal. This is an uncertain parameter (there is very little data available), but we estimated that for current populations to persist, the loss through dispersal mortality needs to be < 40%. We use our model to predict the maximum spread rate of PSHB (discounting transport by humans) to be 3 km/year. Our model provides insights into the spatial and temporal heterogeneity of invasion risk, which will assist global efforts to manage the ongoing invasion of this species.

Life history theory emphasizes that finite resources result in allocation trade-offs among the competing interests of self-maintenance, growth, reproduction, and survival. Environmental conditions, particularly during development, can influence these life history trade-offs, leading to the coupling of physiological and behavioural traits with life history strategies. Thus, populations may vary in the pattern of trait covariation, clustering along a fast-slow continuum, termed the extended pace-of-life syndrome (POLS) theory. We aimed to test how variation in ecological conditions influence life history trade-offs and their association with behaviour and physiology by comparing captive bred and wild-collected southern rainforest sunskink (Lampropholis similis). The captive bred skinks were the offspring of the wild-caught skinks, and all tests were conducted in the laboratory. We found that the groups differed, on average, in growth rate, body condition, thermal preferences, sprint performance, and activity. Counter to our expectation, wild-caught skinks exhibited a faster pace of life relative to captive-bred skinks despite experiencing more challenging environmental conditions. Furthermore, life history trade-offs were not detected, nor were traits correlated to form the syndrome. Studies are needed to identify the proximate mechanisms causing life history trade-offs and how they lead to the coupling, or decoupling, of physiological and behavioural traits. Such information will provide vital insight into how ecological forces drive the evolution of traits.

Exposure to a pathogen is predicted to lead to increased energy use as hosts attempt to activate a costly immune system and repair damaged tissue. To meet this demand, metabolic rates, which capture the rate at which a host can use, transform and expend energy, are expected to increase. Yet for many host–pathogen systems, metabolic rates after encountering a pathogen are just as likely to decrease as increase, suggesting that increased energy expenditure may not always be best for fighting infection. Diverging metabolic trajectories have been previously attributed to the different pathways that specific pathogen classes, such as bacteria or viruses, induce in a host. Here, we test how the magnitude and direction of metabolic change following pathogen exposure might also depend on whether a host has cleared infection or is instead fighting to reduce pathogen burden, as well as interactions between host and pathogen genotypes of a single host–pathogen system. Using a model system, Daphnia magna and its bacterial pathogen, we quantified changes in mass‐independent metabolic rates over a 30‐day period for multiple host and pathogen genotypes. We found that the metabolic trajectory of an exposed host diverged quickly during the infection process. For hosts that were exposed to a pathogen and resisted infection, their mass‐independent metabolic rates remained suppressed long after exposure, leading to a sustained reduction in total energy use compared to unexposed animals. The reverse was true for hosts in which the pathogen was able to establish an infection. Underlying these changes were differences in the energetic burden that each pathogen genotype imposed on its host, as well as changes in the way host genotype and the outcome of infection shaped underlying scaling relationships between host body mass and metabolic rates. Our results demonstrate how variation in an organism's metabolic rate and overall energy use can arise from within a single host–pathogen encounter and depend on the likelihood of pathogen clearance, as well as the within‐species genetic variability of both hosts and pathogens. Read the free Plain Language Summary for this article on the Journal blog.

Targeted gene flow is an emerging conservation approach which involves introducing a cohort of individuals with particular traits to locations where they can produce a conservation benefit. This technique is being proposed to adapt recipient populations to a known threat, but questions remain surrounding how best to maximize conservation outcomes during periods of continuous directional environmental change. Here we introduce a new management objective—to keep the recipient population extant and with maximum diversity of local alleles—and we explore how varying the timing and size of an introduction can maximise this objective. Our results reveal a trade-off between keeping a population extant and maintaining a high level of genetic diversity, but management levers can often optimize this so that nearly 100% of the allelic diversity is preserved. These optimum outcomes sets are highly sensitive to the predicted rate of environmental shift, as well as the level of outbreeding depression in the system.

Developmental environments play a significant role in shaping animal phenotype, including behavior. Within a species, individuals often differ in behavior in a consistent and repeatable way (i.e., demonstrate animal personality). This consistency in behavior can be affected by differences in conditions experienced early in life. It is, however, unclear whether effects of developmental environments on animal personality are driven by changes in within- or between-individual variation. To investigate this, we measured activity, exploration, sociability, and boldness in adult male southern rainforest sunskinks,Lampropholis similis, incubated at either 23 °C or 26 °C, and compared behavioral phenotypes between these incubation treatments. We also compared the behavior of these incubation groups to a cohort of wild-caught skinks to determine whether rearing in captivity also affected the personality of the lizards. Skinks that had been incubated at a higher temperature were more explorative and demonstrated personality in a larger suite of traits compared to lizards incubated at a lower temperature or caught in the wild. These differences among developmental environment were primarily driven by within-individual variation, which tended to be higher among the high incubation treatment. We also found no evidence for a behavioral syndrome in either captive- or wild-reared skinks. Our results suggest the potential for greater behavioral plasticity in skinks incubated at a higher temperature, which may enable them to cope with environmental change, such as climate warming, in the short term. Overall, we show that effects of developmental environment are complex and play a pivotal role in shaping animal personality.Significance statement: Experiences during development are expected to influence how animals develop, including their behavior. We tested early environment effects on behavior in adult southern rainforest sunskinks by comparing lizards incubated at different temperatures as well as comparing those reared in the wild with those reared in captive environments. We found that lizards incubated at the higher temperature were more exploratory. Furthermore, both incubation temperature and captivity/wild-rearing had pronounced effects on the consistency of behavior—in different directions for different traits—demonstrating developmental environments have strong effects on animal personality. Such changes in behavioral traits likely have flow-on effects for the animal’s fitness and biotic interactions.