Noisy communities and signal detection: why do foragers visit rewardless flowers?

Abstract

Floral communities present complex and shifting resource landscapes for flower-foraging animals. Strong similarities among the floral displays of different plant species, paired with high variability in reward distributions across time and space, can weaken correlations between floral signals and reward status. As a result, it should be difficult for foragers to discriminate between rewarding and rewardless flowers. Building on signal detection theory in behavioural ecology, we use hypothetical probability density functions to examine graphically how plant signals pose challenges to forager decision-making. We argue that foraging costs associated with incorrect acceptance of rewardless flowers and incorrect rejection of rewarding ones interact with community-level reward availability to determine the extent to which rewardless and rewarding species should overlap in flowering time. We discuss the evolutionary consequences of these phenomena from both the forager and the plant perspectives. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

Changing How Biologists View Flowers—Color as a Perception Not a Trait

“…As color variability of the mimic is lower than the rewarding species, bees are likely to accept flowers of the mimic as potential variants of W. cuspidata (Figure 6). Such an outcome is consistent with signal theory predictions where an decrease in Type I errors results in an increase of the probability of making Type II errors (Endler and Mappes, 2017;Lichtenberg et al, 2020) highlighting the benefits of using PDFs to the study of plant mimicry.…”

“…Therefore, the color sensation experienced by a bee is frequently context dependant, and as such, cannot be quantified and compared as other purely physical traits. Interestingly, the use of functions like those presented in Figures 3, 4 produce data from physical traits that are compatible with a signal detection theory (Endler and Mappes, 2017;Lichtenberg et al, 2020), which better predict bee behavioral responses when foraging in the presence of rewarding targets and non-rewarding distractor flowers.…”

“…This solution, however, would then increase its chances of accepting non-rewarding mimics resulting in an increase of its Type II error (Endler and Mappes, 2017). Lichtenberg et al (2020) presented a theoretical model explaining the complexity of this scenario using univariate probability density functions (PDFs) to describe the effects of signal variability in both mimic and rewarding species. This is an interesting approach as PDFs better describe the distribution of flower colors in the wild in similar way to that encountered by a foraging bee.…”

“…This is an interesting approach as PDFs better describe the distribution of flower colors in the wild in similar way to that encountered by a foraging bee. The area where two PDFs overlap creates a "confusion" region: signals falling within this area will be ambiguous and potentially difficult to discriminate by a pollinator as it could correspond to either the mimic or an infrequent color signal variant of the rewarding species (Lichtenberg et al, 2020). Here we apply and extend this theoretical model to color signals of wild plants to test if tolerance to perceptual noise, resulting from an increase in discrimination ability through experience and bee pollinator viewing conditions, is a likely explanation to the success of mimic orchid species.…”

Alternative flowers affect model and mimic flower discrimination performance of bumblebees

“…Details of the statistical analysis are shown in electronic Supporting Information, Table S2d 4.4 | Further directions Foragers are often required to process complex sensory inputs to respond to a complex environment. For example, intraspecific signal variability that leads to overlap in the perceived colour between rewarding and non-rewarding flowers (Garcia et al, 2020;Lichtenberg et al, 2020), and the variety in reward distribution across time and space (Lichtenberg et al, 2020) would confuse flower-visitors, and may make it difficult to discriminate between rewarding and non-rewarding flowers. In addition, flower-visitors may forage between rewarding and non-rewarding flowers while simultaneously avoiding cryptic predators such as crab spiders (Ings & Chittka, 2008;Zhang et al, 2019).…”