Reproductive strategies of wild boars (Sus scrofa): Foundations for an effective wildlife management

Wild boar piglet
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Wild boar sows
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The research enclosure
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Researcher in the enclosure
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Wallowing wild boar
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Wallowing sow with piglets
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Wild boar in the winter
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Wild boar tracks in the snow
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A curious look
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The wild boar (Sus scrofa) is a species with enormous reproductive potential.  Reproduction is heavily influenced by the availability of food resources (e.g. mast of beech nuts and acorns).  Wild boars react extraordinarily quickly to constantly changing food availability (pulsed resources) and in addition they can get very old.  The combination of these highly variable life-history parametres make the wild boar a very interesting species to examine for tradeoffs and long-term effects of varying environmental conditions on population development. 

Using an experimental approach we are specifically investigating the reproductive strategies of the wild boar, and in particular the influence of early reproduction.

One of the basic tenets of life-history theory is that a high investment into current reproduction has to be "paid for" with lower future reproductive success or with a shorter lifespan.  However, recent investigations show that there are individuals that can have it both: a long life and a lot of offspring.  From an evolutionary-biology point of view the question arises why such genotypes, which are evidently highly fit from an evolutionary perspective,  do not completely dominate in a population. One possible explanation for these findings is that changing environmental conditions mean that each different genotype (and also phenotype) in a population can take advantage of different types of conditions.  The project´s basic research into evolutionary and ecological processes has great potential to provide practical guidance for the management of populations. 

In mast years of beech or oak wild board find food in abundance and react with early reproduction (sows aged less than a year old).  However, only about half of the young sows (piglet sows) get to reproduce.  But what is their reproductive success in future years?  Is a later start of reproduction only an inevitable consequence of weak physical condition in some of the animals, or are there actually different life-history strategies (genotypes), determined by advantages and disadvantages of early vs. delayed onset of reproduction? Since almost all our knowledge of the reproduction of wild boars is based on hunting bag analysis, we hardly know anything about long-term effects (e.g. tradeoffs) of differences in onset of reproduction in this species. 

Two answer these questions we selected three methodological approaches:

A) Consequences of early reproduction

In a feeding experiment (mast situation in the first year of life) two enclosures are being populated with wild boar sows of the same age.  In the control enclosure the animals are allowed to start their reproduction naturally, while in the experimental enclosure reproduction will be prevented during the sows´ first year of life (no males in the enclosure).  Parametres such as times of farrowing (giving birth) and litter size, as well as weight development of the animals and environmental conditions, will be recorded and compared over a period of three years. 

B) Heredity:  The young animals that are born in the enclosure will be examined over several years to understand the heritability of different parametres of reproduction (e.g. farrowing time, onset of reproduction).  For this purpose the offspring will be released on an annual basis into a hunting reserve and monitored.   During the annual hunting bags the genital tracts of offspring shot by hunters will be examined (to record potential litter size).

C) Population dynamics:  The data we collect will serve to model evolutionary and population-related ecological processes.  These models will become the foundation for efficient management plans for wild boar populations.

Economic benefits

The targeted and scientifically sound management of free-ranging wild boar populations, which has to have as its primary goal the control or reduction of excess populations, is of great economic interest.  High densities of wild boars constitute, e.g., a source of infections and reservoirs of  classic swine fever (and thus a potential danger for pig farms).  Fields and green spaces are considerably damaged by wild boars.  The damages caused by wild boars in Europe are currently estimated at several million Euro per year overall.   When developing suitable hunting strategies, however, it is important to know which individuals within a population should be hunted with what intensity and at what time.  Depending on environmental conditions, the targets may differ, but they are essential to guide population development efficiently and in the desired direction.  Given that to shoot a single wild boar by still hunting can take as much as 20 working hours, it is quite important to concentrate on eliminating those age,- and size-classes of animals that, depending on current conditions, make the biggest contribution to population growth.  

Apart from their economic importance the expected research results also have high potential to contribute to the optimisation of wild boar management in commercial hunting operations.  Wild boars are bred and kept in hunting reserves throughout Europe.   In hunting reserves it is possible to maximise hunting success und increase profitability by selecting appropriate breeding animals and adapting feeding.  In this context it is of interest to determine if and to what extent characteristics such as litter size and fitness are heritable.  Beyond this, knowledge of different reproductive strategies is important, since early onset of reproduction may increase reproductive success in the short term, but may be accompanied by clear disadvantages (such as number and fitness of later offspring) in the long term.  One can assume that the basic life-history research undertaken through this project will be met with great interest throughout Europe.  

Project duration 2011-2015

 
Wild boar sows with piglets
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Scientific contact at FIWI

Priv.Doz. Dr.rer.nat Claudia Bieber, Research Institute of Wildlife Ecology, Vetmeduni Vienna

T. +43 (1) 25077-7230 

Email Claudia Bieber


 

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