Dances with wolves: the demographic consequence of asymmetric competition and intraguild predation in a native-invasive skink system

1. Currently, we lack enough knowledge to fully explain how the impacts of species invasion on native communities are attributed to multifaceted, individual-based behavioral outcomes.

2. Here, we illustrate the long-term population dynamics of the native long-tailed sun skink (Eutropis longicaudata) before and after the invasion of the common sun skink (Eutropis multifasciata). We conducted diet investigation, morphological measurement, and a series of behavioral experiments both in the field and laboratory. We explained how the impacts of the invasive skink on the native skink can cascade towards the population level based on these individual-level behavioral data.

3. We present evidence of competition exclusion of the native skink population resulting from the invasion of the common sun skink. The drastic decline found in the native skink population was largely accounted for by low recruitment, as shown by the decrease in its clutch numbers correspondingly.

4. We also found dominance of the invasive skink in both exploitation competition and intraguild predation. Considering the highly overlapping morphological and dietary niches between the two species, our findings imply that the native skink has undergone strong food competition and predation pressure on its eggs and juveniles.

5. Interestingly, the native skink started to display parental care behavior two years after the invasion event, and its clutch survival rate has recovered since then. The shift in parental care behavior may help the native skink cope with this new predation pressure from the invasive skink.

6. Overall, the two competitive skinks showed low chances of coexisting. The negative population growth of this native skink species may be primarily derived from poor reproductive performance, given a sharp decline in its clutch numbers and its inferiority in exploitation competition, despite rebounding clutch survival rates.