Keystone Species on New Zealand Offshore Islands: Ecological Relationships of Seabirds, Rats, Reptiles and Invertebrates on Cook Strait Islands

10.26686/wgtn.16945393 ◽

2021 ◽

Author(s):

◽

Timothy J Markwell

Keyword(s):

Stable Isotope ◽

Stable Isotope Analysis ◽

C:N Ratio ◽

Isotope Analysis ◽

Keystone Species ◽

Pitfall Trapping ◽

Island Ecosystems ◽

Important Species ◽

Positive Effects ◽

Lower Abundance

<p>The influence of seabirds and rats on island ecosystems was measured to assess the applicability of the keystone species concept for ecology and conservation. Pitfall trapping for lizards and small invertebrates, soil sampling and stable isotope analysis was used to assess the roles played by seabirds and rats on six islands in the Marlborough Sounds. Both abundance and ordinal richness of invertebrates were found to be greater on islands with seabirds than on seabird-free islands. Although lizard distribution was strongly influenced by species-specific habitat requirements, the greatest numbers of lizards recorded in this study were found on seabird-inhabited islands. Although significant differences were not found, the C:N ratio of soils in seabird colonies in this study and at other sites was lower than that at seabird-free sites. Nitrogen stable isotope analysis showed that a proportion of the diet of animals at a range of different levels throughout the island foodweb was derived from seabirds. Rats were found to negate many of the positive effects of seabirds. As well as significantly lower numbers of seabirds, islands with rats had lower abundance of lizards and lower abundance and diversity of mall invertebrates than rat-free islands. Although both seabirds and rats play important roles in island ecosystems, neither conformed to a definition of a keystone species. Theoretical and practical problems were found with the calculation of keystone status for different taxa. Given that important species cannot be shown to be keystones, and that calculation is technically difficult (and maybe impossible) the classification of seabirds, rats, or any other species as keystone is not likely to advance theoretical ecology or assist with conservation management. Attempts to define keystone species were found to be unsuccessful and abandonment of the term was advised.</p>

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Restructuring of nutrient flows in island ecosystems following human colonization evidenced by isotopic analysis of commensal rats

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1805787115 ◽

2018 ◽

Vol 115 (25) ◽

pp. 6392-6397 ◽

Cited By ~ 6

Author(s):

Jillian A. Swift ◽

Patrick Roberts ◽

Nicole Boivin ◽

Patrick V. Kirch

Keyword(s):

Land Use ◽

Stable Isotope ◽

Stable Isotope Analysis ◽

Human Activities ◽

Isotope Analysis ◽

Island Ecosystems ◽

Nutrient Flows ◽

Isotope Data ◽

Human Land Use ◽

Human Colonization

The role of humans in shaping local ecosystems is an increasing focus of archaeological research, yet researchers often lack an appropriate means of measuring past anthropogenic effects on local food webs and nutrient cycling. Stable isotope analysis of commensal animals provides an effective proxy for local human environments because these species are closely associated with human activities without being under direct human management. Such species are thus central to nutrient flows across a range of socionatural environments and can provide insight into how they intersected and transformed over time. Here we measure and compare stable carbon and nitrogen isotope data from Pacific rat (Rattus exulans) skeletal remains across three Polynesian island systems [Mangareva, Ua Huka (Marquesas), and the Polynesian Outlier of Tikopia] during one of the most significant cases of human migration and commensal introduction in prehistory. The results demonstrate widespread δ15N declines across these islands that are associated with human land use, intensification, and faunal community restructuring. Local comparison of rat stable isotope data also tracks human activities and resource availability at the level of the settlement. Our results highlight the large-scale restructuring of nutrient flows in island ecosystems that resulted from human colonization and ecosystem engineering activities on Pacific islands. They also demonstrate that stable isotope analysis of often-ignored commensal taxa can provide a tool for tracking human land use and environmental effects.

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Stable isotope analysis indicates positive effects of river restoration on aquatic-terrestrial linkages

Ecological Indicators ◽

10.1016/j.ecolind.2020.106242 ◽

2020 ◽

Vol 113 ◽

pp. 106242 ◽

Cited By ~ 1

Author(s):

Benjamin Kupilas ◽

Brendan G. McKie ◽

Kathrin Januschke ◽

Nikolai Friberg ◽

Daniel Hering

Keyword(s):

Stable Isotope ◽

Stable Isotope Analysis ◽

River Restoration ◽

Isotope Analysis ◽

Positive Effects

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Stable isotope analysis of marine feeding signatures of Atlantic salmon in the North Atlantic

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp227 ◽

2009 ◽

Vol 67 (1) ◽

pp. 52-61 ◽

Cited By ~ 31

Author(s):

J. Brian Dempson ◽

Victoria A. Braithwaite ◽

Denis Doherty ◽

Michael Power

Keyword(s):

Stable Isotope ◽

Atlantic Salmon ◽

Stable Isotope Analysis ◽

North Atlantic ◽

C:N Ratio ◽

Isotope Analysis ◽

Unknown Origin ◽

Δ13c And Δ15n ◽

The North ◽

The North Atlantic

Abstract Dempson, J. B., Braithwaite, V. A., Doherty, D., and Power, M. 2010. Stable isotope analysis of marine feeding signatures of Atlantic salmon in the North Atlantic. – ICES Journal of Marine Science, 67: 52–61. Differences in the marine feeding of three geographically distinct populations of Atlantic salmon (Salmo salar) in the North Atlantic (Conne River, Newfoundland; Koksoak River, Ungava Bay, Québec; River Erne, northwest Ireland) were examined using analyses of stable isotopes of carbon and nitrogen (δ13C and δ15N) and contrasted with isotope signatures obtained from a sample of salmon of unknown origin captured in the Labrador Sea. Although the overall range of δ13C and δ15N values (δ13C: from −22.42 to −19.37; δ15N: from 10.70 to 13.38) was similar to that reported by others, significant differences were found among populations and between different sea-age life-history groups. Reported differences in marine feeding between populations from the Northeast and Northwest Atlantic corroborated the stable isotope results. A surrogate measure of lipid content, the C:N ratio, was also compared among 1-sea-winter salmon. The highest levels were associated with the Koksoak River, suggesting that Subarctic populations may require higher energy reserves to contend with their longer migrations and more-severe environmental conditions.

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The influence of food quantity on carbon and nitrogen stable isotope values in southern African spiny mice (Acomys spinosissimus)

Canadian Journal of Zoology ◽

10.1139/cjz-2014-0134 ◽

2015 ◽

Vol 93 (5) ◽

pp. 345-351 ◽

Cited By ~ 3

Author(s):

G.N. Robb ◽

S. Woodborne ◽

P.R. de Bruin ◽

K. Medger ◽

N.C. Bennett

Keyword(s):

Stable Isotope ◽

Stable Isotope Analysis ◽

Lipid Extraction ◽

C:N Ratio ◽

Isotope Analysis ◽

Single Species ◽

Carbon And Nitrogen ◽

Food Quantity ◽

Significant Difference ◽

Influence Of Food

Stable isotope analysis is frequently applied as a tool to examine dietary patterns in animals. However, some of the underlying assumptions associated with using this approach are increasingly being questioned. We carried out a controlled diet experiment on the southern African spiny mouse (Acomys spinosissimus Peters, 1852) to test a number of aspects relating to these assumptions and also examine the hypothesis that stable isotopes, especially δ15N, can be used to provide evidence of nutritional stress. We compared the δ13C and δ15N values of livers and blood from animals that were fed ad libitum with animals undergoing a 10% reduction in food supply. Food-restricted animals showed no significant difference in δ15N; however, δ13C values of both liver and blood were depleted. Restricted animals also had a significantly lower C:N ratio. We examined the role of lipids and found following lipid extraction that both livers and lipids still showed the same separation in carbon values. Tissue–diet discrimination values were also calculated and found to be higher for both Δ13C and Δ15N compared with other mice species. Empirical values for discrimination rates were then compared with values calculated using an alternative method based on employing generic values and were found to be dissimilar, suggesting the use of generic values are not always appropriate. Our results highlight the need for greater understanding of the assumptions associated with using stable isotope analysis to examine diet and we suggest that studying a single species under captive conditions presents an ideal method to begin to test these hypotheses.

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