The effects of feral goats (Capra hircus) on island ecosystems

doi:10.1016/0006-3207(78)90038-1

Biological Conservation

Volume 13, Issue 4, June 1978, Pages 279-286

https://doi.org/10.1016/0006-3207(78)90038-1 Get rights and content

Abstract

Feral goats (Capra hircus) are implicated in habitat destruction, and alteration of species composition on sensitive insular ecosystems. In the absence of population control, goats have become the ecologically dominant species on many islands with the results that numerous endemic plant species have been extirpated, or are threatened by excessive grazing. It is demonstrated that removal of goats can lead to rapid recovery of suppressed vegetation. The problems associated with excessive numbers of feral goats have rarely been studied or formally recognised. Extensive and intensive research is critically needed if affected island ecosystem are to be preserved or restored.

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Environmental conditions and resource availability shape population dynamics through direct and indirect effects of climate, biological interactions and the human modification of landscape. Even when a species seems dependent on predictable anthropogenic food resources or subsidies, ecosystem-level factors can still determine population dynamics across taxa. However, there is still a knowledge gap about the cascade effects driven by climate, vegetation functioning, resource availability and governmental policies on key aspects of species reproduction for top scavengers. Here we put to good use 22 years (2000−2021) of extensive population monitoring from the endemic Canary Egyptian vulture (Neophron percnopterus majorensis) on the Fuerteventura Island (Canary Islands, Spain) to study the relative importance of demographic factors, ecosystem conditions and availability of anthropogenic food sources on breeding success. Our results suggest that ecosystem-level primary productivity, the number of livestock animals present on the island and Density-dependent processes determine the temporal changes in the breeding success of this species. We firstly accounted for a top-down effect of livestock on island vegetation, where overgrazing directly reduces landscape-level vegetation biomass. We, consequently, found a bottom-up effect between vegetation and the Egyptian vulture's breeding success. In this context, minimal changes in ecological conditions can impact the species inhabiting these ecosystems, with direct consequences on a key population stage, such as breeding season, when energy requirements are higher. These results are especially relevant because cascading and indirect effects of ecosystem processes and governmental policies are often overlooked when pursuing conservation goals of endangered species.
Knuckle-walking in Sahelanthropus? Locomotor inferences from the ulnae of fossil hominins and other hominoids
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Because the ulna supports and transmits forces during movement, its morphology can signal aspects of functional adaptation. To test whether, like extant apes, some hominins habitually recruit the forelimb in locomotion, we separate the ulna shaft and ulna proximal complex for independent shape analyses via elliptical Fourier methods to identify functional signals. We examine the relative influence of locomotion, taxonomy, and body mass on ulna contours in Homo sapiens (n = 22), five species of extant apes (n = 33), two Miocene apes (Hispanopithecus and Danuvius), and 17 fossil hominin specimens including Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, and early Homo. Ulna proximal complex contours correlate with body mass but not locomotor patterns, while ulna shafts significantly correlate with locomotion. African apes' ulna shafts are more robust and curved than Asian apes and are unlike other terrestrial mammals (including other primates), curving ventrally rather than dorsally. Because this distinctive curvature is absent in orangutans and hylobatids, it is likely a function of powerful flexors engaged in wrist and hand stabilization during knuckle-walking, and not an adaptation to climbing or suspensory behavior. The OH 36 (purported Paranthropus boisei) and TM 266 (assigned to Sahelanthropus tchadensis) fossils differ from other hominins by falling within the knuckle-walking morphospace, and thus appear to show forelimb morphology consistent with terrestrial locomotion. Discriminant function analysis classifies both OH 36 and TM 266 with Pan and Gorilla with high posterior probability. Along with its associated femur, the TM 266 ulna shaft contours and its deep, keeled trochlear notch comprise a suite of traits signaling African ape-like quadrupedalism. While implications for the phylogenetic position and hominin status of S. tchadensis remain equivocal, this study supports the growing body of evidence indicating that S. tchadensis was not an obligate biped, but instead represents a late Miocene hominid with knuckle-walking adaptations.
Eradication of feral goats, not population control, as a strategy to conserve plant communities on Mediterranean islets
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Citation Excerpt :
Of all of the mammals introduced to islands, goats (Capra hircus L.) and rabbits (Oryctolagus cuniculus L.) are some of the most widespread species worldwide (Flux & Fullagar, 1992; Capizzi, 2020). The presence of introduced herbivores affects the whole ecosystem through processes such as predation of plant species, erosion, nitrification, and alteration of the soil composition (Coblentz, 1978; Desender, Baert, Maelfait, & Verdyck, 1998; Campbell & Donlan, 2005) or even interfering with the breeding of marine birds (Imber, Harrison, & Harrison, 2000), among other examples. Overgrazing of insular plant populations by introduced herbivores is more harmful for plant species without defences against herbivory, and in some cases, forces the plants to constrain their habitat (Pisanu, Farris, Filigheddu, & García, 2012) and even threaten critically endangered flora (Menezes de Sequeira, Jardim, Gouveia, Góis-Marques, & Eddie, 2021).
The introduction of mammalian herbivores negatively affects insular vegetation, especially plant species with narrow distributions that are vulnerable to herbivory or that evolved in the absence of native mammal herbivores. Eradication programs have been performed on many islands worldwide, though assessment of the responses of vegetation is crucial to guarantee the success of these programs. In this study, we aimed to evaluate vegetation recovery after a reduction in the feral goat population on Es Vedrà, an islet in the Balearic Islands (Western Mediterranean Basin). We monitored nine permanent plots in three different habitats (rocky areas, grasslands, shrublands) to evaluate the variation in plant coverage, functional traits and diversity indexes over time. We obtained data for each plot by annual field sampling in mid-May of 2016–2019. We observed a significant recovery of the predominant species in each plant community and an increase in many functional traits. We found significant variation in taxonomic diversity in rocky areas and grasslands, but not in shrublands, and functional diversity only varied in rocky areas. Therefore, plant diversity benefited from the reduction in the goat population and functional redundancy increased in rocky areas, improving the capacity to respond against disturbances. However, the reduction in the goat population was not sufficient to preserve plant communities and negative effects reappeared in 2019, coinciding with the increase in the goat population. Therefore, absolute eradication of introduced herbivores represents a unique, efficient strategy to guarantee the ecological restoration of affected habitats in microinsular ecosystems.
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Despite islands contributing only 6.7% of land surface area, they harbor ~20% of the Earth’s biodiversity, but unfortunately also ~50% of the threatened species and 75% of the known extinctions since the European expansion around the globe. Due to their geological and geographic history and characteristics, islands act simultaneously as cradles of evolutionary diversity and museums of formerly widespread lineages—elements that permit islands to achieve an outstanding endemicity. Nevertheless, the majority of these endemic species are inherently vulnerable due to genetic and demographic factors linked with the way islands are colonized. Here, we stress the great variation of islands in their physical geography (area, isolation, altitude, latitude) and history (age, human colonization, human density). We provide examples of some of the most species rich and iconic insular radiations. Next, we analyze the natural vulnerability of the insular biota, linked to genetic and demographic factors as a result of founder events as well as the typically small population sizes of many island species. We note that, whereas evolution toward island syndromes (including size shifts, derived insular woodiness, altered dispersal ability, loss of defense traits, reduction in clutch size) might have improved the ability of species to thrive under natural conditions on islands, it has simultaneously made island biota disproportionately vulnerable to anthropogenic pressures such as habitat loss, overexploitation, invasive species, and climate change. This has led to the documented extinction of at least 800 insular species in the past 500 years, in addition to the many that had already gone extinct following the arrival of first human colonists on islands in prehistoric times. Finally, we summarize current scientific knowledge on the ongoing biodiversity loss on islands worldwide and express our serious concern that the current trajectory will continue to decimate the unique and irreplaceable natural heritage of the world’s islands. We conclude that drastic actions are urgently needed to bend the curve of the alarming rates of island biodiversity loss.

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Biological Conservation

Abstract

References (27)

Vegetational changes in the Galapagos Islands during the period 1966–1973

Biol. Conserv.

The Galapagos giant tortoises (Geochelone elephantopus) Part I: Status of the surviving populations

Biol. Conserv.

The Galapagos giant tortoises (Geochelone elephantopus) Part II: Conservation methods

Biol. Conserv.

Relations between feral goats and vegetation in New Zealand

Goat management problems—Hawaii Volcanoes National Park

US Department of the Interior, National Park Service Research Report

Man as an agent in the spread of organisms

Ecology, behavior, and range relationships of the feral goat

Report on the status and management of game animals, Santa Catalina Island, California

Cacti in the Galapagos Islands, with special reference to their relations with tortoises

The terrestrial ecology of Ascension Island

J. appl. Ecol.

Plant ecology of the Channel Islands of California

Allen Hancock Pacif. Exped.

Extinct and vanishing birds of the world

Spec. Publs Am. Comm. int. Wild Life Prot.

Cited by (138)

Rainfall reduces the potential for competitive suppression of a globally endangered ungulate by livestock

Ecosystem productivity drives the breeding success of an endangered top avian scavenger in a changing grazing pressure context

Knuckle-walking in Sahelanthropus? Locomotor inferences from the ulnae of fossil hominins and other hominoids

Eradication of feral goats, not population control, as a strategy to conserve plant communities on Mediterranean islets

Vertebrate herbivore browsing and impact on forest production

Scientists’ warning – The outstanding biodiversity of islands is in peril