Investigating tritrophic interactions using bioenergetic demographic models

A central debate in ecology has been the long-running discussion on the role of apex predators in affecting the abundance and dynamics of their prey. In terrestrial systems, research has primarily relied on correlational approaches, due to the challenge of implementing robust experiments with replication and appropriate controls. A consequence of this is that we largely suffer from a lack of mechanistic understanding of the population dynamics of interacting species, which can be surprisingly complex. Mechanistic models offer an opportunity to examine the causes and consequences of some of this complexity. We present a bioenergetic mechanistic model of a tritrophic system where the primary vegetation resource follows a seasonal growth function, and the herbivore and carnivore species are modeled using two integral projection models (IPMs) with body mass as the phenotypic trait. Within each IPM, the demographic functions are structured according to bioenergetic principles, describing how animals acquire and transform resources into body mass, energy reserves, and breeding potential. We parameterize this model to reproduce the population dynamics of grass, elk, and wolves in northern Yellowstone National Park (USA) and investigate the impact of wolf reintroduction on the system. Our model generated predictions that closely matched the observed population sizes of elk and wolf in Yellowstone prior to and following wolf reintroduction. The introduction of wolves into our basal grass-elk bioenergetic model resulted in a population of 99 wolves and a reduction in elk numbers by 61% (from 14,948 to 5823) at equilibrium. In turn, vegetation biomass increased by approximately 25% in the growing season and more than threefold in the nongrowing season. The addition of wolves to the model caused the elk population to switch from being food-limited to being predator-limited and had a stabilizing effect on elk numbers across different years. Wolf predation also led to a shift in the phenotypic composition of the elk population via a small increase in elk average body mass. Our model represents a novel approach to the study of predator-prey interactions, and demonstrates that explicitly considering and linking bioenergetics, population demography and body mass phenotypes can provide novel insights into the mechanisms behind complex ecosystem processes

Celebrating wildlife population recovery through education

Large mammal populations are rapidly recovering across Europe, yet people have not readapted to living with wild animals, resulting in human–wildlife conflict. We believe that society should unite to make the most of the instances of nature recovery, and propose science and education as the key to succes

Framework for strategic wind farm site prioritisation based on modelled wolf reproduction habitat in Croatia

In order to meet carbon reduction targets, many nations are greatly expanding their wind power capacity. However, wind farm infrastructure potentially harms wildlife, and we must therefore find ways to balance clean energy demands with the need to protect wildlife. Wide-ranging carnivores live at low density and are particularly susceptible to disturbance from infrastructure development, so are a particular concern in this respect. We focused on Croatia, which holds an important population of wolves and is currently planning to construct many new wind farms. Specifically, we sought to identify an optimal subset of planned wind farms that would meet energy targets while minimising potential impact on wolves. A suitability model for wolf breeding habitat was carried out using Maxent, based on six environmental variables and 31 reproduction site locations collected between 1997 and 2015. Wind farms were prioritised using Marxan to find the optimal trade-off between energy capacity and overlap with critical wolf reproduction habitat. The habitat suitability model predictions were consistent with the current knowledge: probability of wolf breeding site presence increased with distance to settlements, distance to farmland and distance to roads and decreased with distance to forest. Spatial optimisation showed that it would be possible to meet current energy targets with only 31% of currently proposed wind farms, selected in a way that reduces the potential ecological cost (overall predicted wolf breeding site presence within wind farm sites) by 91%. This is a highly efficient outcome, demonstrating the value of this approach for prioritising infrastructure development based on its potential impact on wide-ranging wildlife species

Patterns and processes of recovering large mammal communities

Despite the global biodiversity crisis, some ecosystems are showing encouraging signs of recovery, especially in Europe and North America. We do not have a clear understanding of how ecosystems recover from degraded states, of the causes and consequences of such recovery, or of how emerging species interactions affect and are affected by ecological processes. In this thesis, I investigate the patterns and processes emerging from recovering ecosystems by analysing population dynamics, species interactions and animal movement. I explore the spatiotemporal trends of an expanding large mammal community in the Alps and investigate predator-prey interactions between wolves and their main prey. I assess the permeability of the Alpine landscape for recovering populations, by analysing the impact of natural and anthropogenic factors on the movement of a partially migratory ungulate. Studying species interactions in a dynamic and recovering system such as the Alps is challenging. I therefore focus on the Yellowstone ecosystem to analyse the impact of wolf predation on their prey and on other ecological processes. I develop a mechanistic, bio-energetic model of the vegetation-elk-wolf system, to study how energy acquired through resources flows across trophic levels influencing population dynamics and interactions. I then use this model to study how ecological and evolutionary change can affect complex tri-trophic systems. I show that large mammal communities can recover relatively quickly in the right environment, and with the support of conservation and favourable environmental legislation. Nonetheless, humans can still have a significant impact on animal populations by affecting their movement patterns and habitat use. In the Alps, I could not detect an impact of wolf predation on prey populations because the recovery process is still ongoing and the system is highly dynamic. In Yellowstone, on the other hand, I show that wolf predation can have significant effects on the ecosystem, and that complex trophic interactions can respond in unexpected ways to ecological and evolutionary change. My thesis offers advances for investigating complex terrestrial systems, for predicting the potential impacts of environmental change on ecosystems, and for informing future policy and landscape management decisions

Roads constrain movement across behavioural processes in a partially migratory ungulate

Background: Human disturbance alters animal movement globally and infrastructure, such as roads, can act as physical barriers that impact behavior across multiple spatial scales. In ungulates, roads can particularly hamper key ecological processes such as dispersal and migration, which ensure functional connectivity among populations, and may be particularly important for population performance in highly human-dominated landscapes. The impact of roads on some aspects of ungulate behavior has already been studied. However, potential differences in response to roads during migration, dispersal and home range movements have never been evaluated. Addressing these issues is particularly important to assess the resistance of European landscapes to the range of wildlife movement processes, and to evaluate how animals adjust to anthropogenic constraints. Methods: We analyzed 95 GPS trajectories from 6 populations of European roe deer (Capreolus capreolus) across the Alps and central Europe. We investigated how roe deer movements were affected by landscape characteristics, including roads, and we evaluated potential differences in road avoidance among resident, migratory and dispersing animals (hereafter, movement modes). First, using Net Squared Displacement and a spatio-temporal clustering algorithm, we classified individuals as residents, migrants or dispersers. We then identified the start and end dates of the migration and dispersal trajectories and retained only the GPS locations that fell between those dates (i.e., during transience). Finally, we used the resulting trajectories to perform an integrated step selection analysis. Results: We found that roe deer moved through more forested areas during the day and visited less forested areas at night. They also minimized elevation gains and losses along their movement trajectories. Road crossings were strongly avoided at all times of day, but when they occurred, they were more likely to occur during longer steps and in more forested areas. Road avoidance did not vary among movement modes, and during dispersal and migration, it remained high and consistent with that expressed during home range movements. Conclusions: Roads can represent a major constraint to movement across modes and populations, potentially limiting functional connectivity at multiple ecological scales. In particular, they can affect migrating individuals that track seasonal resources, and dispersing animals searching for novel range

Roads constrain movement across behavioural processes in a partially migratory ungulate

Background Human disturbance alters animal movement globally and infrastructure, such as roads, can act as physical barriers that impact behaviour across multiple spatial scales. In ungulates, roads can particularly hamper key ecological processes such as dispersal and migration, which ensure functional connectivity among populations, and may be particularly important for population performance in highly human-dominated landscapes. The impact of roads on some aspects of ungulate behaviour has already been studied. However, potential differences in response to roads during migration, dispersal and home range movements have never been evaluated. Addressing these issues is particularly important to assess the resistance of European landscapes to the range of wildlife movement processes, and to evaluate how animals adjust to anthropogenic constraints. Methods We analysed 95 GPS trajectories from 6 populations of European roe deer (Capreolus capreolus) across the Alps and central Europe. We investigated how roe deer movements were affected by landscape characteristics, including roads, and we evaluated potential differences in road avoidance among resident, migratory and dispersing animals (hereafter, movement modes). First, using Net Squared Displacement and a spatio-temporal clustering algorithm, we classified individuals as residents, migrants or dispersers. We then identified the start and end dates of the migration and dispersal trajectories, and retained only the GPS locations that fell between those dates (i.e., during transience). Finally, we used the resulting trajectories to perform an integrated step selection analysis. Results We found that roe deer moved through more forested areas during the day and visited less forested areas at night. They also minimised elevation gains and losses along their movement trajectories. Road crossings were strongly avoided at all times of day, but when they occurred, they were more likely to occur during longer steps and in more forested areas. Road avoidance did not vary among movement modes and, during dispersal and migration, it remained high and consistent with that expressed during home range movements. Conclusions Roads can represent a major constraint to movement across modes and populations, potentially limiting functional connectivity at multiple ecological scales. In particular, they can affect migrating individuals that track seasonal resources, and dispersing animals searching for novel ranges

Density dependent environments can select for extremes of body size

Body size variation is an enigma. We do not understand why species achieve the sizes they do, and this means we also do not understand the circumstances under which gigantism or dwarfism is selected. We develop size-structured integral projection models to explore evolution of body size and life history speed. We make few assumptions and keep models simple: all functions remain constant across models except for the one that describes development of body size with age. We set sexual maturity to occur when size attains 80% of the asymptotic size, which is typical of a large mammal, and allow negative density dependence to only affect either reproduction or juvenile survival. Fitness -- the quantity that is maximized by adaptive evolution -- is carrying capacity in our models, and we are consequently interested in how it changes with size at sexual maturity, and how this association varies with development rate. The simple models generate complex dynamics while providing insight into the circumstances when extremes of body size evolve. The direction of selection leading to either gigantism or dwarfism crucially depends on the proportion of the population that is sexually mature, which in turn depends on how the development function determines the survivorship schedule. The developmental trajectories consequently interact with size-specific survival or reproductive rates to determine the best life history and the optimal body size emerges from that interaction. These dynamics result in trade-offs between different components of the life history, with the form of the trade-off that emerges depending upon where in the life history density dependence operates most strongly. Empirical application of the approach we develop has potential to help explain the enigma of body size variation across the tree of life

A greener path for the EU common agricultural policy

A greener path for the EU common agricultural polic

Impacts of the Common Agricultural Policy (CAP) on biodiversity and ecosystem services

As part of a ‘fitness check’ evaluation of the Common Agricultural Policy (CAP), completed in autumn 2017, we conducted an in depth literature review to evaluate both direct and indirect effects of the CAP on biodiversity (BD) and ecosystem services (ESS). Beyond instruments that are designated towards the protection of BD and ESS, such as agri-environment(-climate) schemes (AECM), greening, and cross compliance (CC), we considered and evaluated non-designated instruments such as Direct Payments, that likely have indirect effects on BD and ESS by affecting land-use changes, farm structure and management. Although literature suggests that AECM can be locally effective (1), their effectiveness at the EU level remains limited due to a restricted budget and extent, low uptake and acceptance by farmers, lack of spatial design, and poor implementation in many cases. Greening measures are both ineffective and cost-inefficient since most farmers are either exempt or can comply with the greening requirements without any action (2). Additionally, administrative requirements bias farmers toward choosing the simplest and least effective measures (3) and management requirements and spatial design are lacking. With respect to supporting farming systems that can be considered as sustainable, our review indicates that the CAP offers adequate support to promote organic farming, but much greater support is given to unsustainable farming systems. Moreover, the protection of High Nature Value farming systems is scarce and inadequate. Concerning ESS, current measures (AECM, CC) are somewhat effective with respect to soil protection and water quality but the performance of the CAP is very low with regard to climate issues by failing to address the most important sources of greenhouse-gas emissions, namely livestock production and nitrogen fertilization. Overall, the CAP’s design and implementation poorly takes up existing knowledge and experience with respect to necessary interventions and best indicators, and its various instruments operate with little coherence (e.g. AECM and organic farming) or even in conflict (e.g. AECM and greening). Moreover, the CAP only marginally addresses the EU's global ecological footprint and its contribution to land-use changes outside of Europe. Thus, the global efficiency and effectiveness of the CAP in terms of BD and ESS remains weak. Our literature review indicates the availability of a wealth of evidence to inform current and future policy design processes. Integration of all available knowledge, in collaboration with the scientific community, will be essential for achieving higher effectiveness, efficiency, and coherence within instruments and among the CAP and the EU’s biodiversity strategy. A much more inclusive, transparent and evidence-based process will be necessary if the European Commission wishes to address the concerns over the CAP’s performance with respect to public goods.peerReviewe