Examination of the fish faunas of estuaries in New Zealand suggests that they have resident faunas of low diversity. However the estuaries serve as pathways in the migrations of a few marine fish species and a wide range of freshwater fish species. For this reason it is important that estuaries remain free from pollution and habitat modification
The concept of ecosystem engineering has been proposed recently to account for key processes between organisms and their environment which are not directly trophic or competitive, and which result in the modification, maintenance and/or creation of habitats. Since the initial reporting of the idea, little work has been undertaken to apply the proposed concept to potential ecosystem engineers in the marine environment.
Replacing native forests and grasslands with plantations, pastures and crops has resulted in both contraction of ranges and exploitation of modified habitats by native species, and both general and restricted dispersal of introduced species of soil fauna. Contraction is shown by native earthworms, land snails, ring nematodes and various arthropods, while the areas with changed land use suggest certain native insects are more numerous than 150 years ago. Damage to pastures by grass grub and porina show clearly how native species can exploit modified habitats.
Understanding the factors that drive population persistence and growth is fundamental to both conservation management and evolutionary biology. Internal (maternal) and external (environmental) factors can affect female reproductive output, and in oviparous reptiles both may strongly influence offspring phenotype and quality. However, the link between these effects, their importance for reproductive output and offspring characteristics of live-bearing lizards, and whether population declines are linked to these factors in modified versus native habitats are unknown.
