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The consequences of the joint individual variation in size specific life histories and behavioural types

Periodic Reporting for period 1 - BT-LH Link (The consequences of the joint individual variation in size specific life histories and behavioural types)

Reporting period: 2015-06-01 to 2017-05-31

No individuals of a group of animals are identical. Individuals in a population differ among each other in a variety of characteristics. It is commonly known that individuals vary among each other for example in their growth rate, their size or age at which they reach maturity, the rate of this reproduction etc. Such life history traits determine the fitness of an individual and the variation in traits among individuals have recently been shown to also influence the dynamics of populations and communities and how they respond to change in the environments the individuals experience. Understanding the causes and consequences of individual trait variation is an important endeavor for ecology and evolutionary biology. Such an understanding is crucial for successful species conservation or for the sustainable management of animal populations for their recreational and economic benefits to human well being.
It is increasingly accepted that animals not only differ in their life history traits but that they also differ substantially in the behaviours they display and that this behaviour is less flexible than previously assumed. Instead the differences in behaviours among individuals are often highly consistent over time and over situations, leading to the establishment of stable variation in behavioural traits among individuals of the same populations, so called behavioural types. It has been suggested that behavioural types may be coupled to individual life history traits and that behaviour and life history traits together influence individual fitness and population and communities.
The overall objective of the action was to investigate the emergence of the hypothesised link between behavioural types and life history traits over the development of individuals from juveniles to adults, how the link is influenced by environmental conditions like food availability and to assess the consequences of the link for population dynamics and the management of natural resources.
To this aim we used a variety of approaches, reaching from literature reviews and the development of a conceptual framework to manipulative experiments at various levels and over different time spans. We conclude that indeed the coupling between behavioural types and life history traits can affect the dynamics of animal populations and can also affect the management of exploited populations. We also found that more research is required to exactly understand when and how the behavioural type - life history link is important.
We used a variety of approaches to achieve the objectives, including manipulative experiments with a fish species at various levels and over different time spans but also literature reviews and the development of a conceptual framework. We found that behavioural types in the model species Heterandria formosa exist and that they are stable over the period from juveniles to adulthood. As individual fish grow and become older, behavioural types become more stable and the differences among fish become more pronounced, suggesting a role of experiences acquired over life and the accumulation of small stimulus over life. The emergence of behavioural types was not in all of the measured behaviours influenced by the environment the individuals were exposed to, but exploration and boldness was affected by food availability: fish that experienced a chronic food shortage explored more and were bolder, but this effect of the rearing environment manifested only in later, adult stages. Fish from low food environments were also less stable in their exploration type, suggesting that a higher behavioural flexibility may be of advantage under environmental stress. The link between behavioural types and life history traits existed, but only for traits of adults, which seems in line with that in the adults stage behaviour was most sensitive to environmental cues. These results are currently prepared for publication.
We also found out with the help of an experiment that in the absence of hetero- and conspecific competitors and natural enemies and in a familiar setting, behavioural types in exploration and boldness do not influence individual feeding rates. Because feeding is necessary to acquire the energy and matter for growth and reproduction this finding suggests that behavioural types may influence individual fitness and life histories not in all circumstances.
We published a literature review on the several ecological and managerial consequences of behavioural types for social groups, populations, food webs, fisheries and stock assessment under human exploitation that employs passive gear. Using the here developed framework of the so called timidity syndrome which can be a result of the behavioural types – life history link, we identified further research activities necessary to deepen our understanding of how exploited fish populations respond to behaviourally selective harvesting.
We also used the timidity syndrome framework to propose that consumptive nature-based tourism might lead to behavioral outcomes opposed to those so far proposed in the literature. We argue that the exploitation animal populations exploited in nature-based tourism like recreational angling induces a timidity syndrome rather than increasing the boldness level of the exploited populations.
As befits a basic research program such as ours the results and findings of the action were mainly disseminated via publications in scientific, peer-reviewed journals, the participation in scientific conferences and workshops and the invited presentations in seminar and lecture series. We also transferred our results to other research settings.
The action made some important contribution to the state-of-the-art of the field. We identified food availability as a driver of behavioural differences among individuals and a factor that can influence the development of behavioural types over the development time of individuals from juveniles to adults. This finding will help to understand the emergence and maintenance of behavioural types under various environmental conditions.
We also for the first time provided individual-level estimates of feeding rates and used the data to test the influence of behavioural types on feeding rates. Such individual-level tests are important when trying to understand the impact of trait variation on population and community dynamics.
By developing a new framework on the effects of exploiting natural populations via induced behavioural changes we outlined the consequences behavioural types can have for social and population dynamics, for food webs and the management of exploited populations. We already employed that framework successfully to discuss the impacts of consumptive, nature-based tourism on exploited populations.
The action’s main goal was to perform basic research. However, the findings of the action will help to better understand the impacts of behavioural types and behaviorally selective exploitation on exploited populations, benefiting the sustainable management of such populations.
a picture of the model organism, Heterandria formosa, used in the action