Interactions among species and ecosystems determine their responses to scale-specific fluctuations

Ecosystems are highly connected systems with many interacting components. Understanding the mechanisms creating ecosystem patterns requires an explicit consideration of the scales at which interactions among species and their environments occur. This dissertation focuses on the scale of temporal variability and how temporal variability is incorporated into communities’ dynamics. I first derive an abstract theory that describes the general patterns of variability propagation within communities. Next, I explore the role of species’ interaction strengths on community dynamics across time scales. Finally, I study the impact of human-induced hydrological changes of the Guadalquivir River on the European anchovy fishery in the Gulf of Cadiz.Chapter 1 uses linear response theory to extend the top down and bottom up views of ecology across time scales. Specifically, I study a tri-trophic food chain and how fluctuations in productivity filter up the food chain. I find that variability follows the pattern predicted by top-down equilibrium-based theories at slow time scales. However, at an intermediate time scale, consumers can both decrease and increase the sensitivity of lower trophic levels to variability. For example, perturbations at intermediate frequencies can excite the endogenous cycles of a community leading to resonance. Only at the fastest time scales do top down effects begin to break down as variability becomes dampened at higher trophic levels. This theory provides a robust new framework to interpret food web patterns resulting from resource pulses and other bottom up perturbations. Chapter 2 combines the metabolic theory of ecology and empirical information of consumer-resource interactions to ground the general theory developed in Chapter 1. Body size is not only a significant determinant of vital rates and but also species interaction strengths. This approach allows me to focus on biologically relevant parameter space. I predict that predators can control herbivores and producers\u27 variability at a time scale of days to years. This theory predicts that indirect effects actively shape communities\u27 responses across a wide range of ecologically relevant time scales. Finally, in Chapter 3, I explore the relationship between ecology and society by studying how agricultural water use is connected to the marine anchovy fishery in Spain’s Gulf of Cadiz. Using time series analysis, I explore the correlations between hydrology, the estuarine community, and anchovy recruitment to the Gulf of Cadiz. The Guadalquivir river’s mean annual discharge and seasonality have decreased over the last 90 years due to increasing river regulation and extraction. European anchovies use the river estuary as a nursery. These hydrological changes have reduced anchovy recruitment to the Gulf of Cadiz, connecting terrestrial water use with the marine fishery. I then produce a water allocation theory for terrestrial agriculture and a marine fishery. I predict that even practices that improve water efficiency will not necessarily prevent terrestrial ecosystems from total water consumption. I find that the protection of downriver ecosystem services is only protected when the benefits to marine ecosystems are considered nonsubstitutable with terrestrial ecosystems. The issue of scale – ecological and spatiotemporal – is at the heart of my thesis. My first chapter shows that the percolation of variability is not invariant across time scales. In my second chapter, I predict how body size drives differences in community responses to variability. These theories can provide new insights into how variability impacts communities. Finally, in my last chapter, I explore rivers and migration can create trade-offs between seemingly isolated ecosystems

Structure and functional composition of macroinvertebrate communities in coastal plain streams across a precipitation gradient

Climate change is expected to alter rainfall and temperature regimes across the world. The hydrology and riparian zone vegetation of lotic ecosystems are tightly linked to rainfall and a mechanistic understanding of the effects of rainfall on lotic ecosystems is needed to forecast the ecological impacts of climate change. However, it is difficult to isolate rainfall effects from other environmental variables that covary across climates. To address this, we leveraged a unique steep rainfall gradient with few covarying changes in elevation, temperature, and geology to evaluate the effects of rainfall on stream invertebrate communities. We surveyed nine streams in the Texas Gulf Coast Prairie distributed along a 550–1,350 mm/year rainfall gradient. Four sites were classified as drier semi-arid streams (\u3c750 mm annual rainfall) and five sites were classified as wetter sub-humid streams (\u3e750 mm annual rainfall). A suite of characteristics including benthic invertebrate community metrics, flow conditions, and water quality variables were assessed monthly for 14 months at each site to relate precipitation regime to stream structure and function. Precipitation regime was observed to be a master explanatory variable. As annual rainfall increased, the flow environment became more stable within seasons and predictable across seasons, influencing spatial structure and temporal variability of invertebrate community composition. Wetter streams were dominated by slower growing taxa without adaptions for desiccation resistance and strong dispersal. Wetter sites displayed seasonal variation in community composition and species richness, whereas temporal variation in communities in drier streams was controlled by stochastic variation in flow conditions. These observations show that differences in local annual rainfall correlated with major changes to community structure and functional composition. We hypothesise that this association is related to the connection of rainfall to hydrological stability, particularly the frequency of low flow disturbances, and the subsequent effects on riparian vegetation and temporally available niches to stream invertebrates. Our work adds to evidence that alterations in precipitation patterns associated with climate change have sweeping impacts on lotic fauna

Pattern and process in metabolic ecology : from biotic interactions to cultural diversity gradients

Many ecological patterns and processes are functions of metabolism (Brown 2004), meaning the acquisition, transformation, and allocation of energy, materials, and information within the bodies of individuals and among members of human and other animal societies. Individual metabolic rate should influence behavior by determining the energy available for action as well as the rate at which the body requires fuel. First, I test a key prediction of the metabolic theory of ecology (MTE), that biotic interaction rates are characteristic functions of temperature. Findings support this prediction and suggest that herbivory, predation, parasitism, parasitoidy, and competition increase exponentially with temperature and that this increase echoes that of individual metabolic rates. Second, I extend a metabolic framework to foraging patterns and space use of traditional human societies. Together with colleagues, I build on Hamilton (2007) to offer a model that formally incorporates hypothesized mechanisms affecting population sizes and densities and territory sizes: temperature, productivity, seasonality, and trophic level (degree of carnivory). We test this model on a dataset of 333 traditional foraging societies using multiple linear regression. Interactions between explanatory variables were important, and the influence of temperature, productivity, and seasonality often depended on trophic level. In addition, coastal productivity allowed marine foragers to disassociate themselves from terrestrial energetic constraints and maintain high population densities, small territory sizes, and thus high levels of cultural diversity. A metabolic perspective is useful for interpreting patterns in large scale human ecology and suggesting underlying mechanisms. Third, I argue for a macroecological approach to human ecology and suggest the value of a metabolic perspective using examples from human foraging ecology, life history, space use, population structure, disease ecology, cultural and linguistic diversity patterns, and industrial and urban systems. The ability of a metabolic framework to inform our understanding of behavior, from the interaction rates of small ectotherms to cultural diversity and urban activity patterns in Homo sapiens, suggests the power and promise of this approach

The role of diet in vole population cycles

To upubliserte artikler har blitt fjernet fra den digitale versjonen, og kan leses i den trykte avhandlingen./Two unpublished articles have been removed from this digital version, and can be read in the printed thesis.Smågnagerpopulasjoner med store bestandssvingninger finner vi over hele verden. I denne avhandlingen har jeg inkludert en litteraturstudie om både regelmessige sykluser og mer uregelmessige utbrudd i smågnagerpopulasjoner og som peker på de viktigste problemstillingene å svare på for videre forståelse (Paper I). Smågnagere i boreale, alpine og arktiske økosystem er særlig kjent for sine sykliske populasjonsendringer, hvor både sesongvariasjon og/eller endringer i mattilgang er viktige faktorer. I et observasjonsstudium i de boreale skogene på Evenstad, fant vi en klar sammenheng mellom høyde over havet og hvor mye smågnagere det var i museårene. Smågnagerpopulasjonen hadde et syklisk forløp over hele høydegradienten, men syklusen var tydeligst høyt oppe i liene der det var mer mus i toppåret enn det var nede i dalene og bekreftet slik den viktige rollen vintersesongen spiller (Paper II). En tydelig tetthetsavhengighet om vinteren er forventet ved begrensede ressurser. En systematisk gjennomgang av litteraturen om forholdet mellom smågnagere og planter (Paper III) viste at begrenset mattilgang kan påvirke smågnagernes populasjonstetthet, og at det var best støtte for dette om vinteren. Det var derimot ikke mulig å hverken bekrefte eller avkrefte noen «plantehypothese» på grunn av for få studier med like respons- og forklaringsvariabler. Begge litteraturstudiene (Paper I og Paper III) poengterer viktigheten av at fremtidige studier utforsker videre om det forekommer systematiske endringer i dietten til smågnagerne som kan påvirke deres populasjonsdynamikk. Jeg har forsøkt å belyse nettopp dette ved å ta i bruk DNA-strekkoding (metabarcoding) for å analysere om diettens komposisjon eller diversitet endrer seg systematisk i forhold til sesong og syklusens faser (Paper V). DNA-strekkoding kan dog ikke forventes å reflektere relative proporsjoner av matinntaket nøyaktig (Paper IV). Diettstudien fant stor fleksibilitet i dietten, noe som støtter opp under at det forekommer moderate endringer mellom sesong og faser hos både klatremus Myodes glareolus og fjellmarkmus Microtus oeconomus. Men diettvariasjonen som kan tilskrives syklusenes faser var relativt marginal i forhold til den generelle fleksibiliteten i dietten. Det virker derfor ikke sannsynlig at fasenes diettvariasjon er tilstrekkelig for å drive smågnagerpopulasjonenes særegne dynamikk.Abstract: Small rodent populations throughout the world show massive density fluctuations. In this thesis, I have included a review highlighting the most critical issues essential for understanding the generality of small rodent population cycles and outbreaks (Paper I). Herbivorous voles in boreal, alpine, and arctic ecosystems are especially renowned for their multi-annual population cycles in which both seasonality and plant-herbivore interaction may play an important role. Using observational data from a boreal ecosystem, the importance of seasonality was confirmed in Paper II where winter length was positively associated with the amplitude of vole population cycles. Strong density dependence during winter is expected if resources are limited. Indeed, a systematic literature review focusing on plant-rodent interactions (Paper III) found the most robust evidence for food resource dependency during winter. However, the evidence was scattered across study systems to such a degree that only a few specific topics were addressed in a replicated manner. Thus, the hypothesis that interactions with plants cause rodent cycles could not be discarded. Because all hypotheses predicting that plants cause rodent cycles have explicit, yet largely untested, assumptions of diet shifts across population cycles, both review papers (Paper I, Paper III) conclude that one of the essential issues to explore further is whether a diet shift occurs that change population dynamics. I pursued this research question with DNA metabarcoding to quantify diets of two functionally important boreal vole species (Paper V). However, care should be taken when inferring the diet composition obtained by DNA metabarcoding of vole faeces as a direct mirror of the consumed food’s composition (Paper IV). Paper V is the first metabarcoding study to assess whether vole diet composition and diversity change systematically according to season and critical phases of a population cycle. We observed large diet flexibility and tendencies for moderate shifts in the proportions of plant taxa in the diets of bank voles Myodes glareolus and tundra voles Microtus oeconomus both between phases and seasons. Thus, changes do occur through time in vole diet composition, although the temporal change at population level appeared to be minor compared to other sources of diet variation. Overall, this study indicates that the variation in diet that could be attributed to cyclic phases is marginal relative to the overall diet flexibility. Hence, it seems unlikely that temporal variation in diets is driving the transition between increase/peak and crash/low phase of the population cycle.publishedVersio

The importance of seasonality at different levels of ecological organization in the marine ecosystem of the Northwestern Mediterranean Sea

[eng] From an oceanographic perspective, seasonality has been widely studied, and abundant research exists about low trophic level organisms such as phytoplankton and zooplankton. Nevertheless, at a regional scale, this information is not always homogenous and certain areas lack longer time series to track seasonal cycles. This knowledge gap is emphasized as one moves to higher trophic level organisms, whose studies tend to focus on single seasons or inter-annual variation rather than on seasonal changes and intra-annual dynamics. This Ph.D. thesis aims to broaden the knowledge about the marine ecosystem of the Northwestern Mediterranean Sea incorporating the importance of seasonality in key ecological processes, such as body condition, fitness, spatial distribution, and trophic ecology of marine species, and, finally, the structure and functioning of marine food webs. Seasonality is approached at different levels of the marine community, including the demersal component focusing on commercially important species of fish (Merluccius merluccius, Lophius budegassa, Lophius piscatorius, Mullus barbatus), crustaceans (Liocarcinus depurator, Squilla mantis) and cephalopods (Illex coindetii, Eledone cirrhosa), the pelagic component targeting the most abundant and commercially important small pelagic fish species (Sardina pilchardus and Engraulis encrasicolus), and at the ecosystem level using system indicators. To attain these objectives, various methodological approaches have been combined, such as species distribution models, stable isotopes analysis, bayesian isotope mixing isotope models, analysis of biometrical/biophysical parameters (Kn, GSI, fat content), generalized additive models and ecosystem modelling. Results show seasonal variations in species distribution with species-specific patterns in the case of demersal species. Bathymetry, temperature and fishing effort are important drivers explaining biomass spatial distribution of these species. European hake is further studied in one of the chapters, and the predicted posterior mean weight distribution also presents spatial differences between winter and summer. Ontogenetic and seasonal variations are also detected in the diet of this species. Spatial and seasonal variations in fitness are found at the local scale for European sardines and anchovies. These changes are mostly explained by environmental variables while spatial and seasonal factors are also important. Moreover, trophic variables also contributed to the species dynamics, suggesting that variations in prey abundance, composition and quality can impact their fitness. At the ecosystem level, we investigate changes in indicators of ecosystem structure and functioning when using seasonal input data vs annual averages in marine ecosystem models for the characterization of our study area. We find several indicators showing significant variations in ecosystem structure and energy transfer. Overall, the findings of this Ph.D. show seasonal variation at different levels of biological organization and in various ecological processes, which highlights the relevance of seasonality in the marine realm, specifically in the Northwestern Mediterranean Sea. Therefore, we can conclude that considering seasonality in ecological studies can provide complementary insights into our understanding of species biological and ecological dynamics, which cascades up to the knowledge about ecosystem structure and functioning.[spa] Desde una perspectiva oceanográfica y climatológica, la estacionalidad se ha estudiado ampliamente y existen múltiples investigaciones desarrolladas con organismos situados en niveles tróficos bajos, como el fitoplancton y el zooplancton. Sin embargo, a escala regional, esta información no siempre es homogénea y algunas zonas carecen de series temporales largas. Esta laguna de conocimiento se acentúa a medida que se avanza hacia organismos de nivel trófico superior. Esta tesis pretende mejorar el conocimiento sobre el ecosistema marino del mar Mediterráneo noroccidental investigando el efecto de la estacionalidad en algunos procesos ecológicos clave, como la condición corporal, la distribución espacial y la ecología trófica de las especies, así como en la estructura y el funcionamiento de las redes tróficas marinas. La estacionalidad se aborda a distintos niveles de la comunidad marina, incluyendo el componente demersal (especies de peces, crustáceos y cefalópodos), pelágico (la sardina y el boquerón) y a nivel de ecosistema. Para alcanzar estos objetivos, se han combinado diversos enfoques metodológicos (e.g. modelos de distribución de especies, análisis de isótopos estables, análisis de parámetros biométricos/biofísico y modelización de ecosistemas). Para las especies demersales, los resultados muestran variaciones estacionales en su distribución espacial, y la batimetría, la temperatura y el esfuerzo pesquero aparecen como importantes impulsores. La merluza europea se estudia con más detalle en uno de los capítulos y se detectan variaciones ontogenéticas y estacionales en la dieta de esta especie. En el caso de la sardina y el boquerón, se observan variaciones espaciales y estacionales en la condición a escala local. Estos cambios se explican principalmente por variables ambientales y los factores espaciales y estacionales, pero las variables tróficas también contribuyen. A nivel de ecosistema, investigamos los cambios en los indicadores de estructura y funcionamiento de los ecosistemas al utilizar datos de entrada estacionales, frente a medias anuales. Encontramos varios indicadores que muestran variaciones significativas en la estructura del ecosistema y la transferencia de energía. En general, los resultados de esta tesis muestran una variación estacional en diferentes niveles de organización biológica y en varios procesos ecológicos, lo que pone de manifiesto la relevancia de la estacionalidad en el mar Mediterráneo noroccidental. Se concluye que considerar la estacionalidad en los estudios ecológicos puede aportar conocimientos complementarios a la comprensión de la dinámica biológica y ecológica de las especies, y a la estructura y el funcionamiento de los ecosistemas marinos

A mechanistic approach to understanding the colour polymorphism in black sparrowhawks (Accipiter melanoleucus)

Species that exhibit large variation in phenotypic traits, are commonly considered to have a stronger evolutionary potential. However, how they are capable to maintain polymorphisms remains a fundamental problem in evolutionary biology. Colour polymorphic species provide ideal study systems to explore the processes that lead to variation maintenance. About 3.5% of all bird species are colour polymorphic, but it is an especially common phenomenon in Accipitridae (22%), which indicates that it has an adaptive function in this bird group and makes them ideal model systems to study evolutionary processes. The black sparrowhawk (Accipiter melanoleucus) occurs in two discrete colour variants: dark and light. The two morphs differ in the expression of white and black feathers on the breast, belly and underwing coverts. The morph has been associated with ambient light-dependent foraging success and activity behaviour: Dark morphs forage more and have higher foraging success under low light conditions whereas light morphs forage independently of light levels but are better foragers under bright light conditions. This is hypothesized to be due to a crypsis advantage for the morphs under these conditions. During the winter breeding period, the predominating low light conditions on the Cape Peninsula (Western Cape, South Africa) could create an advantage for dark morphs, which should result in their higher survival and higher breeding success. However, this is not the case and only when the two morphs come together to breed, there is a fitness difference: mixed-morph pairs (that consist of a dark and a light morph) have higher breeding success than like-morph pairs (that consist of the same morph) and offspring of mixed-morphs have higher survival rates. This higher success of mixed-morph pairs is hypothesized to be due to emergent pair-level properties with the two morphs being able to expand the hunting niche as a pair. This ‘complementarity hypothesis' is based on previous research conducted on the study system. The aim of this PhD was to explore the mechanistic background of colour polymorphism maintenance in the black sparrowhawk. (i) I performed an experiment in which I test whether there is a morph- and ambient light-dependent crypsis advantage in the black sparrowhawk. I measure the reaction time of feral pigeons towards a simulated hawk attack but did not find indication of such an effect as pigeons reacted the same towards the two morphs. In line with the complementarity hypothesis, (ii) I found that mixed-morph parents provide food more consistently to the nest than like-morph parents. This results in a more predictable food supply for nestlings and buffers against long periods of malnourishment. However, (iii) I was unable to determine the mechanistic link between food supply and higher survival: nestlings of mixedand like-morph pairs had the same levels of innate immune function. Thus, an improved innate immune function in nestlings of mixed-morph pairs is unlikely associated with their higher survival rates. (iv) I performed individual-based model simulations which incorporate multiple key fitness parameters and found that complementarity – in combination with morphdependent seasonality-associated fitness effects – explains the stable colour morph equilibrium in this population. I conclude that emergent pair-level properties which arise due to the complementary nature of the two morphs play an important role in maintaining polymorphism in this species. Complementarity might not only be restricted to colour polymorphic species but could be present in other polymorphic traits that allow parents to behaviourally complement each other when raising their young

The Influence of River Discharge on Fishes and Invertebrates Associated with Small Oil and Gas Platforms in Nearshore Louisiana

The nearshore region off Louisiana’s coast is one of the most productive areas in the United States. Nutrient-rich discharge from the Mississippi and Atchafalaya rivers forms the base of this productivity, but it also contributes to the annual formation of a large hypoxic zone (DO \u3c 2.0 mg l-1). This region contains \u3e900 oil and gas platforms (platforms) that are de facto artificial reefs and support fish and invertebrate communities. In this dissertation, I examined how select platform-associated fishes and invertebrates responded to river-driven productivity and hypoxia. Settlement plates were used to compare barnacle production at depths of 2 and 7-m along a 43.9 km landward-seaward transect with decreasing river influence. Amphibalanus reticulatus settlement and growth decreased with increased distance from shore and was generally higher at 2 than 7-m. Total accumulation of fouling organisms decreased at rates of -9.8 to -1.2 g m-2 d-1 km-1, depending on depth and year. A video array was used to estimate abundances and depth distributions of fishes before, during, and after summer hypoxia at platforms experiencing intense (seaward) and mild hypoxia (shoal). Occupation of bottom waters by fishes was consistent throughout the study period at shoal platforms, but fishes were rarely observed in the bottom 3-m when hypoxia was present at seaward platforms. However, patterns of fish abundances were not driven by the presence or absence of hypoxia. A different camera array was used to characterize fish foraging at platforms. Sheepshead, Gray Snapper, Horse-eye Jack, Atlantic Spadefish, and Black Drum were observed foraging on fouling organisms, but Sheepshead was the only fish that consistently foraged on platforms (88.9% of samples). Mixing-models of Sheepshead stable isotopes (δ13C and δ15N) indicated their diet was not negatively affected by hypoxia, but gut contents suggested they temporarily exploited prey that were vulnerable because of hypoxia. Barnacles represented 64.1% of gut contents and stable isotopes suggested that barnacles and filamentous algae were 79.2 ­– 83.0% of their prey. Secondary production at platforms was increased by high primary productivity associated with river discharge. However, hypoxia influenced distributions of platform-associated organisms and temporarily increased Sheepshead exploitation of benthic prey

Influences of Pacific Island human communities on benthic coral reef functioning and resilience

A multitude of local and global stressors are threatening the diversity and productivity of coral reef ecosystems within the current era of the Anthropocene. While the effects of global stressors on coral reefs are relatively well understood, the role of various local human impacts and their interaction with global stressors remains under debate. By using a combination of observational-, theoretical- and secondary data-based approaches, this thesis aimed to improve understanding of relationships between local human impacts and benthic coral reef communities in the understudied Pacific Island region. Particularly, it addressed how various levels and types of local impacts can directly and indirectly influence benthic coral reef functioning and in turn future resilience to global stressors

Ecological mechanisms driving the anti-predator defense response in Crucian carp (Carassius carassius): Variation in morphology, resource use, and life-history strategies along a gradient of predation risk

© Ilaria de Meo (2021). Faculty of Applied Ecology, Agricultural Sciences and Biotechnology, Inland Norway University of Applied Sciences (INN), Department of Forestry and Wildlife Management, Evenstad, NorwayPredation is one of the main structuring forces of freshwater communities, influencing population dynamics, phenotypic variation, resource use, and life-history traits within and among prey populations. In order to counteract predation risk, prey organisms may display several anti-predator morphological and behavioral adaptations. The crucian carp (Carassius carassius) represents a classic example of predator-induced morphological defense, as it develops a deep body to decrease vulnerability to predation. Very few studies, however, have explored the ecological drivers underlying morphological variation observed among crucian carp populations in the wild. This PhD thesis aimed at revealing the effects of predation risk on morphology, resource use, and life-history traits of crucian carp along a natural gradient of predation risk. The study was performed in fifteen small lakes from southern Norway, which presented no predators or increasingly efficient gape-limited predators: brown trout, perch, or pike. The results show that crucian carp is provided with a fine-tuned morphological defense response against gape-limited predators. Progressively efficient predators determined an increase in crucian carp relative body depth and size, a decrease in population density, rapid growth at young age, larger lifespans, and higher reproductive effort. Predation pressure likely reduced fish abundance, relaxing intraspecific resource competition and favoring individual growth of survivors. High-predation lakes also corresponded to productive systems with high food availability and complex vegetated littoral habitats. Reduced intraspecific competition, larger food availability, and increased habitat complexity associated with predation risk favored energy allocation to both growth and reproduction. Plastic feeding habits and a shift to more energetically rewarding prey with increasing body size may also have supported this energy allocation. Thus, the expression of the defense response in crucian carp was likely a result of the synergistic effects of predation risk and favorable environmental conditions.Sammendrag: Predasjon er en av de viktigste kreftene som strukturerer økosystemene i ferskvann, gjennom sin effekt på populasjonsdynamikk, fenotypisk variasjon, ressursbruk, og livshistorietrekk mellom og innen populasjonene av byttedyr. For å redusere risikoen for å bli spist kan byttedyrene utvise mange ulike antipredator-strategier, som for eksempel morfologiske og atferdsmessige tilpasninger. Utviklingen av en høy kroppsform hos karuss (Carassius carassius) er et klassisk eksempel på en predatorindusert morfologisk tilpasning (forsvar mot predasjon) for å unngå å bli spist av rovfisk. Det er imidlertid få studier som har undersøkt hvilke økologiske drivere som ligger bak den morfologiske variasjonen vi finner mellom ulike karusspopulasjoner i naturen. Denne PhD-avhandlingen har hatt som mål å finne ut hvordan predasjonsrisiko langs en naturlig gradient påvirker karussens morfologi, ressursbruk og livshistorietrekk. Studien ble gjennomført i femten små karussvann i Østlandsområdet, som varierte fra ikke å ha predatorer til stede til å ha predatorer med en økende grad av effektivitet (basert på størrelsen til fiskens gap): brun ørret (Salmo trutta), abbor (Perca fluviatilis) og gjedde (Esox lucius). Resultatene viser at karuss har en fininnstilt morfologisk forsvarsrespons mot rovfisk, som henger sammen med størrelsen på gapet til predatoren. Med økende effektivitet (gap) hos predatoren økte karussen i størrelse og relativ kroppshøyde, populasjonstettheten sank, veksten ble raskere i ung alder, livslengden økte og den reproduktive innsatsen økte. Det ser ut som om predasjonspress reduserer forekomsten av karuss, letter den intraspesifikke konkurransen om ressurser og favoriserer den individuelle veksten hos de som overlever. De vannene som hadde den høyeste graden av predasjon var også de mest produktive med høy tilgang på føde og med komplekse habitater i form av omfattende strandvegetasjon. Predasjonsrisiko ga redusert intraspesifikk konkurranse, mer tilgjengelig føde og økende habitatkompleksitet. Dette førte til mer energi til både vekst og reproduksjon. Varierende fødehabitat og et skifte til mer energirik føde som følge av økende kroppsstørrelse kan også ha bidratt til denne omfordelingen av energi. Det er altså sannsynlig at karussens forsvarsrespons er et resultat av synergi mellom effekten av predasjonsrisiko og fordelaktige miljøbetingelser.publishedVersio