Modlmeier A.P.,University of Pittsburgh |
Keiser C.N.,University of Pittsburgh |
Watters J.V.,San Francisco Zoological Society |
Sih A.,University of California at Davis |
Pruitt J.N.,University of Pittsburgh
Animal Behaviour | Year: 2014
The concept of keystone individuals offers a unifying framework to study the evolution and persistence of individuals that have a disproportionately large, irreplaceable effect on group dynamics. Although the literature is teeming with examples of these individuals, disparate terminologies have impeded a major synthesis of this topic across fields. To allow a strict classification of potential keystone individuals, we offer herein some general terminology, outline practical methodological approaches to distinguish between keystone individuals and generic individuals that only occupy a keystone role, and propose ways to measure the effect of keystones on group dynamics. In particular, we suggest that keystone individuals should be classified as 'fixed' or 'episodic' according to the duration of time over which they impact their group. We then venture into the existing literature to identify distinctive keystone roles that generic and/or keystone individuals can occupy in a group (e.g. dominant individual, leader or superspreader), and describe traits that can give rise to keystone individuals. To highlight the ecological implications, we briefly review some of the effects that keystone individuals can have on their group and how this could affect other levels of organization such as populations and communities. In looking at their diverse evolutionary origins, we discuss key mechanisms that could explain the presence of keystone individuals. These mechanisms include traditional Darwinian selection on keystone-conferring genotypes, experience and state- or context-dependent effects. We close our review by discussing various opportunities for empirical and theoretical advancement and outline concepts that will aid future studies on keystone individuals. © 2013 The Association for the Study of Animal Behaviour.
Clements J.,San Francisco Zoological Society |
Sanchez J.N.,University of California at Davis
Zoo Biology | Year: 2015
This research aims to validate a novel, visual body scoring system created for the Magellanic penguin (Spheniscus magellanicus) suitable for the zoo practitioner. Magellanics go through marked seasonal fluctuations in body mass gains and losses. A standardized multi-variable visual body condition guide may provide a more sensitive and objective assessment tool compared to the previously used single variable method. Accurate body condition scores paired with seasonal weight variation measurements give veterinary and keeper staff a clearer understanding of an individual's nutritional status. San Francisco Zoo staff previously used a nine-point body condition scale based on the classic bird standard of a single point of keel palpation with the bird restrained in hand, with no standard measure of reference assigned to each scoring category. We created a novel, visual body condition scoring system that does not require restraint to assesses subcutaneous fat and muscle at seven body landmarks using illustrations and descriptive terms. The scores range from one, the least robust or under-conditioned, to five, the most robust, or over-conditioned. The ratio of body weight to wing length was used as a "gold standard" index of body condition and compared to both the novel multi-variable and previously used single-variable body condition scores. The novel multi-variable scale showed improved agreement with weight:wing ratio compared to the single-variable scale, demonstrating greater accuracy, and reliability when a trained assessor uses the multi-variable body condition scoring system. Zoo staff may use this tool to manage both the colony and the individual to assist in seasonally appropriate Magellanic penguin nutrition assessment. © 2015 Wiley Periodicals, Inc.