http://hdl.handle.net/1983/1069 Sun, 19 May 2013 16:58:33 GMT 2013-05-19T16:58:33Z http://hdl.handle.net/1983/1806 A technique for measuring petal gloss, with examples from the Namaqualand flora Whitney, HM; Rands, SA; Elton, NJ; Ellis, Allan G The degree of floral gloss varies between species. However, little is known about this distinctive floral trait, even though it could be a key feature of floral biotic and abiotic interactions. One reason for the absence of knowledge is the lack of a simple, repeatable method of gloss measurement that can be used in the field to study floral gloss. A protocol is described for measuring gloss in petal samples collected in the field, using a glossmeter. Repeatability of the technique is assessed. We demonstrate a simple yet highly accurate and repeatable method that can easily be implemented in the field. We also highlight the huge variety of glossiness found within flowers and between species in a sample of spring-blooming flowers collected in Namaqualand, South Africa. We discuss the potential uses of this method and its applications for furthering studies in plant-pollinator interactions. We also discuss the potential functions of gloss in flowers. Tue, 10 Jan 2012 00:00:00 GMT http://hdl.handle.net/1983/1806 2012-01-10T00:00:00Z http://hdl.handle.net/1983/1797 The dynamics of honesty: modelling the growth of costly, sexually-selected ornaments Rands, SA; Evans, Matthew R; Johnstone, Rufus A The handicap principle suggests that individuals of superior quality can more easily bear the cost of developing extravagant ornaments. Consequently, ornament size should provide reliable information about quality or condition. Previous models have largely ignored the process of ornament growth, focusing only on final ornament size. We model ornament growth schedules for individuals of different qualities, where higher quality individuals experience lower costs of carrying energy reserves of a given size, but where all individuals pay a net cost of carrying ornaments of a given size. If the costs of ornament production ensure that final ornament size reliably signals quality, the information conveyed by the signal can change dramatically during growth. Higher quality individuals should delay growth until closer to breeding. Taking a snapshot of partially developed ornaments prior to breeding would show them to be larger in poorer quality individuals. The claim that costly ornaments honestly signal quality thus needs to be understood in a dynamic context, and may only hold during some phases of growth. Wed, 02 Nov 2011 00:00:00 GMT http://hdl.handle.net/1983/1797 2011-11-02T00:00:00Z http://hdl.handle.net/1983/1796 The effects of dominance on leadership and energetic gain: a dynamic game between pairs of social foragers Rands, SA Although social behaviour can bring many benefits to an individual, there are also costs that may be incurred whenever the members of a social group interact. The formation of dominance hierarchies could offer a means of reducing some of the costs of social interaction, but individuals within the hierarchy may end up paying differing costs dependent upon their position within the hierarchy. These differing interaction costs may therefore influence the behaviour of the group, as subordinate individuals may experience very different benefits and costs to dominants when the group is conducting a given behaviour. Here, a state-dependent dynamic game is described which considers a pair of social foragers where there is a set dominance relationship within the pair. The model considers the case where the subordinate member of the pair pays an interference cost when it and the dominant individual conduct specific pairs of behaviours together. The model demonstrates that if the subordinate individual pays these energetic costs when it interacts with the dominant individual, this has effects upon the behaviour of both subordinate and the dominant individuals. Including interaction costs increases the amount of foraging behaviour both individuals conduct, with the behaviour of the pair being driven by the subordinate individual. The subordinate will tend to be the lighter individual for longer periods of time when interaction costs are imposed. This supports earlier suggestions that lighter individuals should act as the decision-maker within the pair, giving leadership-like behaviours that are based upon energetic state. Pre-existing properties of individuals such as their dominance will be less important for determining which individual makes the decisions for the pair. This suggests that, even with strict behavioural hierarchies, identifying which individual is the dominant one is not sufficient for identifying which one is the leader. Thu, 20 Oct 2011 00:00:00 GMT http://hdl.handle.net/1983/1796 2011-10-20T00:00:00Z http://hdl.handle.net/1983/1794 Field margins, foraging distances and their impacts on nesting pollinator success Rands, SA; Whitney, HM The areas of wild land around the edges of agricultural fields are a vital resource for many species. These include insect pollinators, to whom field margins provide both nest sites and important resources (especially when adjacent crops are not in flower). Nesting pollinators travel relatively short distances from the nest to forage: most species of bee are known to travel less than two kilometres away. In order to ensure that these pollinators have sufficient areas of wild land within reach of their nests, agricultural landscapes need to be designed to accommodate the limited travelling distances of nesting pollinators. We used a spatially-explicit modelling approach to consider whether increasing the width of wild strips of land within the agricultural landscape will enhance the amount of wild resources available to a nesting pollinator, and if it would impact differently on pollinators with differing foraging strategies. This was done both by creating field structures with a randomised geography, and by using landscape data based upon the British agricultural landscape. These models demonstrate that enhancing field margins should lead to an increase in the availability of forage to pollinators that nest within the landscape. With the exception of species that only forage within a very short range of their nest (less than 125 m), a given amount of field margin manipulation should enhance the proportion of land available to a pollinator for foraging regardless of the distance over which it normally travels to find food. A fixed amount of field edge manipulation should therefore be equally beneficial for both longer-distance nesting foragers such as honeybees, and short-distance foragers such as solitary bees. Mon, 03 Oct 2011 00:00:00 GMT http://hdl.handle.net/1983/1794 2011-10-03T00:00:00Z