Breaking and remaking a seed and seed predator interaction in the introduced range of Scotch Broom (Cytisus scoparius) in New Zealand

Introduced plants may initially experience enemy release but some of those interactions may be reinstated through biological control. These cases provide opportunities to explore the dynamics of broken and re-made consumer-resource interactions. The European shrub broom (Cytisus scoparius) was introduced to New Zealand without a specialist seed predator (Bruchidius villosus) until a biological control programme reinstated this interaction in 1988. Broom produces substantially larger seeds throughout its non-native range and there are differences in seedling establishment beneath broom canopies between the native and introduced ranges. We hypothesised that large broom seeds produce seedlings with a survival advantage in shaded conditions, consistent with establishment under broom canopies in the introduced range. We also predicted that the seed-feeding beetle would experience increased fitness in larger seeds. We found that seedling survival was correlated with seed weight in shaded cond...