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Cache protection and decision making in the cape ground squirrel (Xerus inauris)


Samson, Jamie. Cache protection and decision making in the cape ground squirrel (Xerus inauris). 2016, University of Zurich, Faculty of Science.

Abstract

Caching food provides a variety of benefits to an individual, such as the build up of reserves for periods when resources are depleted or to gain a disproportionate amount of an ephemeral resource. One of the risks to adopting this strategy is the potential for theft from food stores, by both conspecifics and/or other species. To reduce this theft, some species have evolved a range of cache protection mechanisms, such as placing food out of site of competitors. In this thesis, I examined various cache protection and decision-making processes exhibited by the Cape ground squirrel (Xerus inauris), a social rodent. Due to the sociality of this species, and therefore, the potential for high rates of cache loss, I predicted they would use a diverse range of behaviours to increase the survivability of stored food.
I first described the natural caching behaviours of the Cape ground squirrel in their natural habitat. This species increased caching frequency just after the heaviest periods of rainfall, indicating that this behaviour might be controlled by the availability of food. They cache around a central burrow system, which classifies their cache type as “scatter hoarding”. In the second study, I investigated the effect of group size on caching and recovery behaviours. Group size in these ground squirrels showed daily fluctuations, and an increased number of individuals in a group had a negative impact on food cache survival. In response to fluctuations in group size, individuals did not change the spatial arrangement of caches, but I argued that this arrangement was a by-product of optimal cache placement and not a method to protect caches. With increased social competition, the ground squirrels seemed to maximise payoffs from food by consuming rather than caching items. The third study, focused on determining whether the cachers were sensitive to the attentive state of nearby conspecifics. Conspecifics were often observed competing with cachers immediately after a cache was deposited, and therefore ensuring audience members are inattentive to the cache event would decrease the chance a cache was stolen. There was a strong preference for individuals to cache when audience members were inattentive to the cache event. In addition, higher ranked individuals showed less sensitivity to these audience effects, possibly due to their ability to defend food items from conspecifics. In the fourth study I presented individuals with a choice between two food items of differing value: one item that was always artificially removed when cached and the other item that was not removed when cached. Although the two items only varied with respects to the payoff in caching, individuals reduced the amount of the removed items they both consumed or cached during the choice presentations. This avoidance to choose the removed food occurred over time, indicating that individuals were using information about the item’s payoff during cache recovery and this then impacted on successive decisions. Due to the lack of obvious landmarks at the study site, in the last experiment, I predicted that individuals might use positional cues from the sun as a reference point when caching and recovering food items. When caching food, individuals moved at consistent offset angles from the sun, moving in straight lines from the provisioning point to the cache point. When recovering food, individuals displayed some flexibility in the use of solar cues, which allowed them to retrieve food more efficiently. Food was retrieved sooner if there were a higher number of individuals present in the group.
Overall, this thesis highlights the variety of decision-making processes individuals must undertake when caching food to ensure maximum profitability. I answered a number of questions on when animals cache, the decisions about what to cache and where to place caches. As this species is social, this decision-making is highly influenced by group members. This thesis provides much needed knowledge on the cache protection strategies used by mammals, where the majority of work has been conducted on birds. Research such as this will hopefully encourage other studies on mammals to determine how social living can lead to the evolution
of counterstrategies to protect food stores.

Abstract

Caching food provides a variety of benefits to an individual, such as the build up of reserves for periods when resources are depleted or to gain a disproportionate amount of an ephemeral resource. One of the risks to adopting this strategy is the potential for theft from food stores, by both conspecifics and/or other species. To reduce this theft, some species have evolved a range of cache protection mechanisms, such as placing food out of site of competitors. In this thesis, I examined various cache protection and decision-making processes exhibited by the Cape ground squirrel (Xerus inauris), a social rodent. Due to the sociality of this species, and therefore, the potential for high rates of cache loss, I predicted they would use a diverse range of behaviours to increase the survivability of stored food.
I first described the natural caching behaviours of the Cape ground squirrel in their natural habitat. This species increased caching frequency just after the heaviest periods of rainfall, indicating that this behaviour might be controlled by the availability of food. They cache around a central burrow system, which classifies their cache type as “scatter hoarding”. In the second study, I investigated the effect of group size on caching and recovery behaviours. Group size in these ground squirrels showed daily fluctuations, and an increased number of individuals in a group had a negative impact on food cache survival. In response to fluctuations in group size, individuals did not change the spatial arrangement of caches, but I argued that this arrangement was a by-product of optimal cache placement and not a method to protect caches. With increased social competition, the ground squirrels seemed to maximise payoffs from food by consuming rather than caching items. The third study, focused on determining whether the cachers were sensitive to the attentive state of nearby conspecifics. Conspecifics were often observed competing with cachers immediately after a cache was deposited, and therefore ensuring audience members are inattentive to the cache event would decrease the chance a cache was stolen. There was a strong preference for individuals to cache when audience members were inattentive to the cache event. In addition, higher ranked individuals showed less sensitivity to these audience effects, possibly due to their ability to defend food items from conspecifics. In the fourth study I presented individuals with a choice between two food items of differing value: one item that was always artificially removed when cached and the other item that was not removed when cached. Although the two items only varied with respects to the payoff in caching, individuals reduced the amount of the removed items they both consumed or cached during the choice presentations. This avoidance to choose the removed food occurred over time, indicating that individuals were using information about the item’s payoff during cache recovery and this then impacted on successive decisions. Due to the lack of obvious landmarks at the study site, in the last experiment, I predicted that individuals might use positional cues from the sun as a reference point when caching and recovering food items. When caching food, individuals moved at consistent offset angles from the sun, moving in straight lines from the provisioning point to the cache point. When recovering food, individuals displayed some flexibility in the use of solar cues, which allowed them to retrieve food more efficiently. Food was retrieved sooner if there were a higher number of individuals present in the group.
Overall, this thesis highlights the variety of decision-making processes individuals must undertake when caching food to ensure maximum profitability. I answered a number of questions on when animals cache, the decisions about what to cache and where to place caches. As this species is social, this decision-making is highly influenced by group members. This thesis provides much needed knowledge on the cache protection strategies used by mammals, where the majority of work has been conducted on birds. Research such as this will hopefully encourage other studies on mammals to determine how social living can lead to the evolution
of counterstrategies to protect food stores.

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Additional indexing

Item Type:Dissertation
Referees:Manser Marta B, van Schaik Carolous, Townsend Simon W
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:May 2016
Deposited On:14 Feb 2017 09:12
Last Modified:14 Feb 2017 18:54
Number of Pages:143
Funders:University of Zurich
Free access at:Related URL. An embargo period may apply.
Related URLs:http://www.recherche-portal.ch/ZAD:default_scope:ebi01_prod010786356 (Library Catalogue)

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