ACCE DTP Annual Meeting, Liverpool, October 2017

Poster from the annual meeting of the ACCE Doctoral Training Partnership, on my research of temporal variability in spatial foraging behaviour of kittiwakes

Transcript

1. Right place at the right time: Spatial & temporal variation in habitat selection by a central place forager Alice M Trevail, Jonathan A Green, Jonathan Sharples, Jeffrey Polton, John Arnould & Samantha C Patrick Q: Does spatial habitat selection by kittiwakes change over the tidal cycle? Q: Does environmental variability increase effect of tidal cycle on spatial habitat selection? Methods M1. Linear mixed effects models to compare used habitat from GPS tracking and available habitat, generated for 10 random points per used location from within foraging range per year. Binomial response: habitat use (available = 0 or used = 1). Fixed effects in 3- way interaction: physical environment (distance to colony or depth), tidal state and colony. Random effects: bird ID, trip ID & year as factor per colony. Model selection by AIC. M2. GPS tracking of breeding adult kittiwakes at: Puffin Is. 2010-11 & 2015-16, n = 49; Skomer Is. 2016-17, n = 14; Rathlin Is. 2017, n = 17 M3. Bathymetry data from the UKHO Data Archive Centre for bathymetric surveys (2-4m resolution from boat surveys) and integrated with GEBCO (global grid at 30” resolution). M4. Difference in marginal R2 when interaction between tide and environment removed from RSF at each colony separately. Models as in M1, without colony as fixed effect, and year as random effect only if multiple years. M5. Tidal cycle split by flow rate and direction: 1) Low: >5 hours either side of HW; 2) flood: 5-1 hours before HW; 3) high: 1 hour either side of HW; and 4) ebb: 1-5 hours after HW M6. Environmental variability based on proximal depth and Depth normalised shear stress (τ) caused by tidal velocity, which is a measure of turbulence caused by tidal flow. We take this as a proxy for the extent to which tidal flow alters the foraging environment over the tidal cycle. High tidal stress values = high tide-driven turbulence at maximum tidal velocities during the tidal cycle, which in turn indicates a bigger alteration to the physical foraging environment. ANOVAs with post-hoc Tukey tests to determine differences in environment within the maximum foraging area of kittiwakes at each colony. Compared mean values, standard deviation and range of values as an indication of environmental heterogeneity References 1. Matthiopoulos et al. (2015) Ecol. Monogr. 85: 413-436 2. Christensen-Dalsgaard et al. (2017) Mar. Biol. 164:196 3. Cox et al. (2016) Royal Soc. Open Sci. 3: 160317 4. Brierley (2014) Curr. Biol.; 24: R1074-R1076 5. Yamamoto et al. (2008) Anim. Behav.; 76: 1647-1652 6. Zamon (2003) MEPS; 261: 243-255 7. Chivers et al. (2013) Biol. Cons.; 164: 73-81 8. Ladd et al. (2005) Fish. Oceanogr. 14: 178-195 9. Wanless et al. (2007) Prog. Oceanogr.; 72: 30-38 1. Spatial landscape characteristics e.g. habitat type2 & productive areas3 2. Predictable temporal cycles e.g. seasonal resource changes4 & day-night changes in predation risk5 Habitat selection: key behaviour linking animals to required resources1. Occurs in response to: Is there an interaction? Can animals adapt spatial foraging behaviour to a predictable temporal cycle that may change resource availability? Aim: Unknown at fine temporal scale relative to foraging decisions • First example of changing habitat selection over a short temporal cycle relevant to animal movement decisions • Highlights importance of environmental heterogeneity and temporal cycles in spatial analyses Results: Habitat selection functions M1 from kittiwake GPS tracking M2 Puffin Island Skomer Island Rathlin Island Environmental variability M6 Increases Increases Effect of tide on habitat selection A: Yes, kittiwake spatial habitat selection changes over the tidal cycle A: Yes, environmental variability increases effect of tidal cycle on spatial habitat selection Distance to the colony Full model R2 = 0.68 All colonies: Kittiwakes prefer to remain close to the colony Water depth M3 Full model R2 = 0.18 All colonies: Depth preference reflects depths close to colony All colonies: Greater preference of deep water during low tide Puffin Island Skomer Island Rathlin Island 0 20 40 0.00 0.25 0.50 0.75 1.00 Distance to colony (km) Probability of habitat use Tidal state M5 Low Flood High Ebb 0 20 40 0 20 40 Variance explained by tide M4 = 1.5 % Var. explained by tide = 2.0 % Var. explained by tide = 7.5 % 0 50 100 150 0.00 0.25 0.50 0.75 1.00 Water depth (m) 0 50 100 150 0 50 100 150 Probability of habitat use Var. explained by tide = 0.6 % Var. explained by tide = 1.8 % Var. explained by tide = 2.1 % Adjacent to colony: shallow Select for: shallow water Adjacent to colony: shallow Select for: shallow water Adjacent to colony: deep Select for: deep water Study system Spatial habitat selection: 1. Distance to the colony – central place foragers7 2. Depth – may effect prey availability & accessibility8 Kittiwakes: Important indicator species9 Predictable 12-hour cycle Tidal coupling hypothesis6: Tidal currents + bathymetry Predictable ocean features Zooplankton distribution Predator foraging behaviour Rathlin Is. Puffin Is. Skomer Is. Gradient of environmental variability: 1. Tidal variability 2. Bathymetry variability Hypothesis = Environmental variability Change in prey over tidal cycle Change in predator behaviour