Animal Personalities: Consequences for ecology and evolution

Max Wolf & Franz Weissing, 2012, Trends in Ecology and Evolution

Behavioural studies have traditionally focused on variation at a population or species level. Until recently, individual level variation was largely overlooked. Although it was accepted that individuals could adopt alternative behavioural strategies, any further variability was considered noise (Smith & Blumstein 2008).  In the past decade the idea of "animal personalities" has gained momentum. Animal personalities are defined as differences in behavioural tendencies which are constant over time and correlated across different contexts (Wolf & Weissing 2012). This is distinct from the concept of behavioural strategy  because while strategies usually only apply in a singular context, personalities are multifaceted and occur across multiple contexts (Smith & Blumstein 2008). Examples of personality traits include exploration tendency, boldness, docility, activity, aggressiveness, impulsivity and fearfulness (Smith & Blumstein 2008; Wolf & Weissing 2012)

While many studies have examined the occurrence, form and cause of personality differences. Surprisingly, very few studies have examined the consequences of personalities. This review article was written for the purpose of filling this gap in the knowledge. Specifically, the authors sought to assess whether personality differences could have implications for large scale ecological and evolutionary processes.

Wolf & Weissing (2012) address this issue by examining 14 potential implications of animal personality differences. These proposed implications were diverse, ranging from effects on spatial distribution to speciation. One of the better supported implications was that animal personality traits (such as exploration and boldness) affect dispersal tendency. Such an assertion is supported observation that individuals which portray appropriate 'behavioural syndromes' tend to be more frequent during the early stages of invasion (Carere & Gherardi 2013). 

 At the end of the day, these 14 consequences boil down to four key assertions (Wolf & Weissing 2012).

1. Personality differences enhance biodiversity 
2. Personality traits are linked to species distribution
3. Personalities lead to structured variation which could have evolutionary consequences
4. Personality differences lead to the emergence of other forms of individual variation including differences in life history, physiology, neurology and disease.

Discussion Group Reception

The first point raised by the EcoEvo discussion group was the confusing distinction between personality and behavioural strategy. By definition, personalities have consistency between different contexts while behavioural strategies tend to address a single situation. Unfortunately, this was not clearly articulated within the article. The authors use the term ‘animal personality’ interchangeably with ‘behavioural difference’ which creates ambiguity. To make things even more confusing, some of their chosen examples appear to more closely fit the definition of behavioural strategy e.g. labour division in meercats. While such critique of terminology may seem finicky, we believed this inconsistency made it hard to discern the overall message of the article.

The paper was also criticised on the grounds that many of its conclusions lacked firm evidence. The authors of this paper did acknowledge this limitation, however, they did not believe it invalidated any of their arguments. This was not a view held by many at the discussion group. We felt that some of the claims of the article were too far-reaching. This was particularly evident when dealing with the implications at an evolutionary timescale such as speciation, rate of evolution etc.

Following critique of the paper, the discussion turned to focus on how animal personalities could be integrated into conservation and management practices. We identified three main areas that we felt could benefit from examination of individual personalities; control, translocation and captive breeding.

•    Control:  Personality differences leading to variation in bait shyness or disease transmission could be significant when planning control operations to eradicate possums. Réale et al. (2000) showed that individual variation in boldness was associated with willingness to enter baited traps in Big Horned Sheep, perhaps a similar phenomenon is occurs in possums? This would be significant from a control perspective because control techniques tend to target the ‘average’ behaviour of a population. If, for example, 'shyness' was a unusually prevalent within a population, the effectiveness of control
may be compromised.

•    Translocation: Certain personalities may be better suited to reintroduction and translocation e.g.  individuals that are predation savvy (e.g. Black Stilts) or more likely to breed in harsh conditions (e.g. Kakapo) may have greater success. In accordance with this idea, Bremmer-Harrison et al. (2004) found that Swift Foxes whom were judged to be bold in captivity were were less likely to survive more than six months after reintroduction than their non-bold counterparts.

•    Captive Breeding: We suggested that certain personality types may lend themselves more readily to captive breeding programmes. Many studies have actually examined this link between reproductive success and personality. Fearfulness has been correlated with reduced reproductive success in captive cheetahs (Wielebnowski 1999) and boldness has been associated with increased breeding success in female black rhinos (Carlstead 1999)

All and all, we felt that study of animal personality would likely improve management of wild and captive populations. However, we were unsure whether these improvements would be significant enough to justify the required investment of resources.

Questions

Is the concept of ascribing personalities to animals inherently anthropomorphic?

Is there a meaningful distinction between ‘personality’ and ‘behavioural strategy’?

Should we be more selective about what we define as animal personality? a.k.a. Can an insect really have a personality?

Is investigation of personality differences a worthwhile investment from a management perspective (particularly for NZ)? If so, how could personalities be quantified in a standardised manner?


References

Bremner-Harrison, S., Prodohl, P.A. & Elwood, R.W. (2004) Behavioural trait assessment as a release criterion: boldness predicts early death in a reintroduction programme of captive-bred swift fox (Vulpesvelox). Animal Conservation, 7, 313-320.

Carlstead, K., Mellen, J., Kleiman, D.G. (1999) Black rhinoceros (Dicerosbicornis) in U.S. zoos: Individual behaviour profiles and their relationship to breeding success. Zoo Biology, 18, 17-34.

Carere, C., Gherardi, F. (2013) Animal personalities matter for biological invasions. Trends in Ecology and Evolution, 28, 5-6.

Réale, D., Gallant, B.Y., Leblanc, M. & Festa-Bianchet, M. (2000). Consistency of tempera-
ment in bighorn ewes and correlates with behaviour and life history. Animal Behaviour, 60, 589-597.

Smith, B.R. & Blumstein, D.T. (2008) Fitness consequences of personality: a meta-analysis. Behavioural Ecology, 19, 448-455.

Wielebnowski, N.C. (1999) Behavioural differences as predictors of breeding status in captive cheetahs. Zoo Biology, 18, 335-349.

Wolf, W. & Weissing, F.J. (2012) Animal personalities: consequences for ecology and evolution. Trends in Ecology and Evolution, 27, 452–461.