Oecologia

, Volume 166, Issue 1, pp 131–140

Population sinks resulting from degraded habitats of an obligate life-history pathway

Population ecology - Original Paper

DOI: 10.1007/s00442-010-1834-7

Cite this article as:
Hickford, M.J.H. & Schiel, D.R. Oecologia (2011) 166: 131. doi:10.1007/s00442-010-1834-7

Abstract

Many species traverse multiple habitats across ecosystems to complete their life histories. Degradation of critical, life stage-specific habitats can therefore lead to population bottlenecks and demographic deficits in sub-populations. The riparian zone of waterways is one of the most impacted areas of the coastal zone because of urbanisation, deforestation, farming and livestock grazing. We hypothesised that sink populations can result from alterations of habitats critical to the early life stages of diadromous fish that use this zone, and tested this with field-based sampling and experiments. We found that for Galaxias maculatus, one of the most widely distributed fishes of the southern hemisphere, obligate riparian spawning habitat was very limited and highly vulnerable to disturbance across 14 rivers in New Zealand. Eggs were laid only during spring tides, in the highest tidally influenced vegetation of waterways. Egg survival increased to >90% when laid in three riparian plant species and where stem densities were great enough to prevent desiccation, compared to no survival where vegetation was comprised of other species or was less dense. Experimental exclusion of livestock, one of the major sources of riparian degradation in rural waterways, resulted in quick regeneration, a tenfold increase in egg laying by fish and a threefold increase in survival, compared to adjacent controls. Overall, there was an inverse relationship between river size and egg production. Some of the largest rivers had little or no spawning habitat and very little egg production, effectively becoming sink populations despite supporting large adult populations, whereas some of the smallest pristine streams produced millions of eggs. We demonstrate that even a wide-ranging species with many robust adult populations can be compromised if a stage-specific habitat required to complete a life history is degraded by localised or more diffuse impacts.

Keywords

Attractive sinksDiadromous fishesGalaxias maculatusHabitat qualitySource-sink dynamics

Supplementary material

442_2010_1834_MOESM1_ESM.pdf (118 kb)
Supplementary material 1 (PDF 118 kb)

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Marine Ecology Research Group, School of Biological SciencesUniversity of CanterburyChristchurchNew Zealand