Turbidity influences individual and group level responses to predation in guppies, Poecilia reticulata

© 2015 The Association for the Study of Animal Behaviour. Increasing turbidity (either sedimentary or organic) from anthropogenic sources has significant negative impacts on aquatic fauna, both directly and indirectly by disrupting behaviour. In particular, antipredator responses of individuals are reduced, which has been attributed to a reduced perception of risk. Here, we explored the effect of turbidity on shoaling behaviour, which is known to carry important antipredator benefits, predicting that fish in turbid water should show reduced shoal cohesion (increased interindividual distances) and reduced responses to a simulated predatory threat. We explored both the individual and shoal level responses to a predation threat at four different levels of turbidity. At the shoal level, we found that shoals were less cohesive in more turbid water, but that there was no effect of turbidity on shoal level response to the predation threat. At an individual level, guppies in turbid water were more likely to freeze (rather than dart then freeze), and those that darted moved more slowly and over a shorter distance than those in clear water. Fish in turbid water also took longer to recover from a predation threat than fish in clear water. We suggest that because fish in turbid water behaved in a manner more similar to that expected from lone fish than to those in a shoal, the loss of visual contact between individuals in turbid water explains the change in behaviour, rather than a reduced perception of individual risk as is widely supposed. We suggest that turbidity could lead to a reduced collective response to predators and a loss of the protective benefits of shoaling

Use of feed-forward mechanisms in a novel research-led module

I describe a novel research-led module that combines reduced academic marking loads with increased feedback to students, and allows students to reflect on and improve attainment prior to summative assessment. The module is based around eight seminar-style presentations (one per week), on which the students write 500-word ‘news & views’ style articles (short pieces highlighting new results to a scientific audience). Students receive individual written feedback (annotated electronically on the work), plus an indicative mark, on their first submitted report. For subsequent reports, only a subset is marked each week, such that each student receives feedback on two further submissions. Simultaneously, they have access to written feedback on their peers’ reports (a total of two reports per student enrolled on the module). Students are encouraged to read and apply the general and specific messages from all the feedback to their own subsequent work (using it as feed-forward). At the end of the module, students self-assess their eight submissions and select the two they believe are their best pieces to put forward for summative assessment. Combining data from three cohorts, student attainment increased throughout the module, with higher marks for the two chosen reports than for the two marked reports or their first report. Students selecting previously unmarked reports also showed a greater increase in their mark for the module than students selecting reports that had previously received a mark. Module evaluation forms revealed that the students found access to feedback on others’ work helpful in shaping their own assignments

Interactive lectures: Clickers or personal devices?

Audience response systems (‘clickers’) are frequently used to promote participation in large lecture classes, and evidence suggests that they convey a number of benefits to students, including improved academic performance and student satisfaction. The limitations of these systems (such as limited access and cost) can be overcome using students’ personal electronic devices, such as mobile phones, tablets and laptops together with text message, web- or app-based polling systems. Using questionnaires, we compare student perceptions of clicker and smartphone based polling systems. We find that students prefer interactive lectures generally, but those that used their own device preferred those lectures over lectures using clickers. However, device users were more likely to report using their devices for other purposes (checking email, social media etc.) when they were available to answer polling questions. These students did not feel that this distracted them from the lecture, instead, concerns over the use of smartphones centred around increased battery usage and inclusivity for students without access to suitable technology. Our results suggest that students generally preferred to use their own devices over clickers, and that this may be a sensible way to overcome some of the limitations associated with clickers, although issues surrounding levels of distraction and the implications for retention and recall of information need further investigation

Turbidity weakens selection for assortment in body size in groups

Prey animals commonly associate with similar-looking individuals to reduce predation risk, via a reduction in predator targeting accuracy (the confusion effect) and preferential targeting of distinct individuals (the oddity effect). These effects are mediated by body size, as predators often preferentially select large-bodied individuals, which are therefore at an increased risk within a group. The selection pressure to avoid oddity by associating with similar sized group mates is stronger for large individuals than small. This selection depends on the ability of both predators and prey to accurately assess body size and respond accordingly. In aquatic systems, turbidity degrades the visual environment and negatively impacts on the ability of predators to detect (and consume) prey. We assessed the effect of algal turbidity on predator–prey interactions in the context of the oddity effect from the perspective of both predator and prey. From a predator’s perspective, we find that 9-spined sticklebacks preferentially target larger Daphnia in mixed swarms in clear water, but not in turbid water, although the difference in attack rates is not statistically significant. When making shoaling decisions, large sticklebacks preferentially associate with size-matched individuals in clear water, but not turbid water, whereas small individuals showed no social preference in either clear or turbid water. We suggest that a reduced ability or motivation to discriminate between prey in turbid water relaxes the predation pressure on larger prey individuals allowing greater flexibility in shoaling decisions. Thus, turbidity may play a significant role in predator–prey interactions, by altering predator–prey interactions

'Selfish herds' of guppies follow complex movement rules, but not when information is limited

Under the threat of predation, animals can decrease their level of risk by moving towards other individuals to form compact groups. A significant body of theoretical work has proposed multiple movement rules, varying in complexity, which might underlie this process of aggregation. However, if and how animals use these rules to form compact groups is still not well under- stood, and how environmental factors affect the use of these rules even less so. Here, we evaluate the success of different movement rules, by comparing their predictions with the movement seen when shoals of guppies ( Poecilia reticulata ) form under the threat of predation. We repeated the experiment in a turbid environment to assess how the use of the movement rules changed when visual information is reduced. During a simulated predator attack, guppies in clear water used complex rules that took multiple neighbours into account, forming compact groups. In turbid water, the difference between all rule predictions and fish movement paths increased, particularly for complex rules, and the resulting shoals were more fragmented than in clear water. We conclude that guppies are able to use complex rules to form dense aggregations, but that environmental factors can limit their ability to do so

Iterated assessment and feedback improves student outcomes

Feedback is critically important to student learning, but the reduced frequency of assignments combined with isolated or stand-alone tasks reduces the opportunity for students to engage with feedback and use it effectively to enhance their learning. Here, I evaluate student attainment during a module consisting of eight iterated tasks where the task itself is the same but the academic content differs. At the end of the module, students then self-assess their eight submissions and select two for summative assessment. I demonstrate that achievement increases over the course of the module, and that choice is valuable in allowing students to achieve higher summative marks for the course than their formative marks would suggest. Students who performed more weakly at the start of the module saw the greatest benefits from practice and choice, suggesting that these students particularly can benefit from repeated cycles of feedback and increase their marks

Ownership conflicts and their resolution

Game theory has been used to investigate a wide range of evolutionary questions, and has been important in explaining apparently selfish patterns in animal behaviour, and behaviours that do not appear to benefit the individual. The modelling chapters in this thesis develop new game theory approaches to modelling animal conflict, investigating the acquisition of territories and the trade-offs that occur between behaviours. Many game theory models of conflicts between individuals make predictions regarding the duration of fights in relation to asymmetries in resource holding potential (RHP). Duration is often interpreted as a result of mutual assessment of RHP, allowing the weaker individual to avoid costly interactions. However, the duration of a contest may also be the result of each individual persisting to a threshold determined by its own RHP, in fiddler crabs, Uca mjoebergi, I show that duration of contests increases with increasing size of the loser, and decreases, but to a lesser extent, with increasing size of the winter, suggesting that neither the mutual assessment or individual threshold hypothesis can explain fight duration in this species. Instead, individual cost thresholds may determine duration, but larger opponents may inflict costs more rapidly, consistent with the cumulative assessment game of animal conflict. In animal contests, the larger opponent is often victorious, but contests are often initiated by individuals that have little chance of winning (generally smaller individuals). A number of hypotheses may explain this behaviour, including a lack of alternative options (the ‘desperado effect’). Recent work has suggested that likely losers attack first due to an error in perception: they mistakenly perceive their chances of winning as being greater than they are. Using a game theoretical model, I show that if smaller individuals can accurately assess their chance of winning, if this chance is relatively high, and if they have few alternative options, they are predicted to be as aggressive as their larger opponents. In addition, when resources are abundant, and small individuals have some change of winning, they may be more aggressive than their larger opponents. Using a game theory model, I show that avoidance of a single fight location can be adaptive if the benefits of access to the area are low compared to the costs of fighting. Low fight costs and high population densities lead to the break down of territoriality and the formation of large, overlapping home ranges

The effect of temporally variable environmental stimuli and group size on emergence behavior

How animals trade-off food availability and predation threats is a strong determinant of animal activity and behavior; however, the majority of work on this topic has been on individual animals, despite the modulating effect the presence of conspecifics can have on both foraging and predation risk. Although these environmental factors (food and predation threat) vary spatially within habitats, they also vary temporally, and in marine habitats, this can be determined by not only the diel cycle but also the tidal cycle. Humbug damselfish, Dascyllus aruanus, live in small groups of unrelated individuals within and around branching coral heads, which they collectively withdraw into to escape a predation threat. In this study, we measured the proportion of individuals in the colony that were outside the coral head before and after they were scared by a fright stimulus and compared the responses at high tide (HT) and low tide (LT). We found that a greater proportion of the shoal emerged after the fright stimulus at HT and in larger groups than at LT or in smaller groups. We also quantified the pattern of emergence over time and discovered the rate of emergence was faster in larger shoals as time progressed. We show that shoals of fish change their behavioral response to a predation threat in accordance with the tide, exemplifying how temporally variable environmental factors can shape group movement decisions

Colour preferences of UK garden birds at supplementary seed feeders

Supplementary feeding of garden birds generally has benefits for both bird populations and human wellbeing. Birds have excellent colour vision, and show preferences for food items of particular colours, but research into colour preferences associated with artificial feeders is limited to hummingbirds. Here, we investigated the colour preferences of common UK garden birds foraging at seed-dispensing artificial feeders containing identical food. We presented birds simultaneously with an array of eight differently coloured feeders, and recorded the number of visits made to each colour over 370 30-minute observation periods in the winter of 2014/15. In addition, we surveyed visitors to a garden centre and science festival to determine the colour preferences of likely purchasers of seed feeders. Our results suggest that silver and green feeders were visited by higher numbers of individuals of several common garden bird species, while red and yellow feeders received fewer visits. In contrast, people preferred red, yellow, blue and green feeders. We suggest that green feeders may be simultaneously marketable and attractive to foraging birds

Consequences of variation in predator attack for the evolution of the selfish herd

There is a strong body of evidence that patterns of collective behaviour in grouping animals are governed by interactions between small numbers of individuals within the group. These findings contrast with study of the ‘selfish herd’, where increasingly complex individual-level movement rules have been proposed to explain the rapid increase in aggregation observed when prey groups are startled by or detect a predator. While individuals using simple rules take into account the position of only a few neighbours, those using complex rules incorporate multiple neighbours, and their relative distance, to determine their movement direction. Here, we simulate the evolution of selfish herd behaviour to assess the conditions under which simple and complex movement rules might evolve, explicitly testing predictions arising from previous work. We find that complex rules outperform simple ones under a range of predator attack strategies, but that simple rules can fix in populations particularly when they are already in the majority, suggesting strong positive frequency dependence in rule success. In addition, we explore whether a movement rule derived from studies of collective behaviour (where individuals use the position of seven neighbours to determine movement direction) performs as successfully as more complex rules, finding again positive frequency dependence in rule success, and a particular role for predator attack strategy (from within or outside the group)