Contrasting responses of lizard occurrences to burrowing by a critically endangered seabird

Abstract

Seabirds are considered ecosystem engineers, because they facilitate ecosystem functioning (e.g., nutrient cycling), crucial for other marine and terrestrial species, including reptiles. However, studies of seabird-reptile interactions are limited. Here, we assessed the influence of the 'Critically Endangered' Whenua Hou Diving Petrel (Pelecanoides whenuahouensis) on the occurrence of two threatened skinks, Stewart Island green skink (Oligosoma aff. chloronoton) and southern grass skink (O. aff. polychroma). We surveyed skinks for 26 consecutive days at 51 sites with and 48 sites without Diving Petrel burrows in the dunes on Codfish Island (Whenua Hou), New Zealand. We used occupancy modelling to assess the influence of burrows on the occurrence of skinks, while accounting for other factors affecting occupancy (Y) and detection probabilities (p). Diving Petrel burrows had a contrasting effect on the occurrence of skinks. On average, Y of Stewart Island green skinks was 114% higher at sites with burrows compared to sites without, while Y of southern grass skinks was only 2% higher. Occurrence of both skinks was negatively influenced by the presence of the other skink species. On average p were low: 0.013 and 0.038 for Stewart Island green and southern grass skinks, respectively. Stewart Island green skinks appear attracted to burrows, which might facilitate thermoregulation (i.e., shelter from temperature extremes). The larger Stewart Island green skinks may subsequently exclude the smaller southern grass skinks at burrows, causing the contrasting relationships. We suggest that these interspecific interactions should be considered when implementing conservation management, e.g., through the order of species reintroductions.

Integrated conservation of the Whenua Hou Diving Petrel

“…I found that the presence of WHDP burrows elevated the occurrence of the larger skink species, in contrast to the smaller species, indicating competition among skink species. These results indicated that WHDP burrowing activity provides benefits to unrelated species groups (Fischer et al 2019). As such, WHDPs may fulfil an important role in the dune systems of southern Aotearoa and this role should be considered in future management strategies.…”

Is habitat enhancement a viable strategy for conserving New Zealand's endemic lizards?

“…In temperate regions, differential thermal strategies of lizard species also explains community structure, with large-bodied species being associated with more vegetated and cooler microhabitats and small and slender species with warmer and more open microhabitats (Scheibe, 1987). Previous studies on New Zealand lizard assemblages suggest that co-existence of lizard species is facilitated by niche partitioning based on habitat and diet preferences, but is also influenced by predation and interference or resource competition (Patterson, 1985;Porter, 1987;Patterson, 1992;Towns and Elliott, 1996;Freeman, 1997;Fischer et al, 2019). Thermoregulatory strategy may also play a role in structuring New Zealand lizard communities.…”

“…Potential consequences of unequal vulnerability to predation within a species assemblage include the alteration of indirect or direct competition dynamics (Holt and Lawton, 1994;Bolnick et al, 2010). Very little is known about interactions between sympatric lizard species in New Zealand, although resource competition, competitive exclusion, and saurivory have been observed (Patterson, 1992;Bell et al, 2012;Evans et al, 2015;van Winkel et al, 2018;Fischer et al, 2019). Competitive interactions between conspecific lizards tend to favour larger individuals, so it is possible that in a case of substantial niche overlap, larger species would have a competitive advantage (Downes and Shine, 1998;Melgren, 2012;Evans et al, 2015).…”

“…Without predator control, it is, at best, a reconciliation measure that could allow co-existence of a species-depauperate endemic lizard community with mammals. However, habitat enhancement could be useful in mammal-free sanctuaries to offset potentially antagonistic relationships between some pairs of lizard species (Patterson, 1985(Patterson, , 1992Phillpot, 2000;Stephens, 2004;Evans et al, 2015;Fischer et al, 2019).…”