Abstract
Managing competing endangered and invasive species in spatially structured environments is challenging because it is often difficult to control invasive species without negatively impacting the endangered species. Effective management action requires an understanding of the factors affecting the presence and absence of each species so that promising sites for relocation of endangered species combined with eradication of invasive species can be identified. We investigate competing hypotheses about the factors affecting occupancy of the critically endangered red‐finned blue‐eye (Scaturiginichthys vermeilipinnis; hereafter ‘RFBE'), a native Australian fish with a global distribution that is restricted to a group of shallow artesian springs. RFBE are threatened by competition with invasive mosquito fish (Gambusia holbrooki), which are steadily colonizing the springs, resulting in local extinctions of RFBE in most cases. While hypotheses about the influences of Gambusia on RFBE exist, none have been tested with a quantitative model. We used a spatially‐structured two‐species occupancy modeling approach to examine the occupancy dynamics of these fish and tested competing hypotheses on how Gambusia occupancy affected RFBE. Gambusia occupancy had a strong negative effect on RFBE occupancy and colonization potential; increasing the probability of local extinction at a spring and decreasing the persistence probability of RFBE in a spring by 8.0% ± 2.7% (mean ± 1 SE). We found strongest support for the hypotheses that elevation and spring area influence colonization, and that spring area influences patch extinction probability. Using colonization and local extinction estimates for both species, we identify promising sites for eradication of Gambusia and relocation of RFBE.
Highlights
Invasive species often outcompete local native species due to competitive exclusion—invasive species are fast colonizers, prolific breeders or aggressive competitors for territory and are adapted to a wide range of conditions that afford them advantages over species that have devel- NICOL ET AL.oped within highly specific environments (Lodge 1993, Mooney and Hobbs 2000)
The probability of colonization by Gambusia decreased with elevation of the spring, while the probability of colonization by RFBE increased with elevation
Competition between species was clearly identified by our model, with all springs showing a reduction in RFBE persistence in the presence of Gambusia
Summary
Invasive species often outcompete local native species due to competitive exclusion—invasive species are fast colonizers, prolific breeders or aggressive competitors for territory and are adapted to a wide range of conditions that afford them advantages over species that have devel- NICOL ET AL.oped within highly specific environments (Lodge 1993, Mooney and Hobbs 2000). The negative effects of competition on the native species can be compounded by other factors that impact its population, especially in the case of critically endangered species. It may be necessary to artificially separate the two competing species, through management intervention, to prevent extinction of the endangered species (Simons et al 1989, Laha and Mattingly 2006). Understanding the factors affecting the balance of colonization and local extinction for both species is important for conservation managers seeking to protect the endangered species (Neubert and Caswell 2000), yet these parameters are often confounded by multiple hypotheses about how the system functions and the species interact Understanding the factors affecting the balance of colonization and local extinction for both species is important for conservation managers seeking to protect the endangered species (Neubert and Caswell 2000), yet these parameters are often confounded by multiple hypotheses about how the system functions and the species interact (Souleet al. 1988, Marsh and Trenham 2001, Gurevitch and Padilla 2004, Krabbe 2004)
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