Species diversity defends against the invasion of Nile tilapia (Oreochromis niloticus)

Abstract

Key-words:Nile tilapia (Oreochromis niloticus), biodiversity resistance, biological invasion, species richness, biomass Nile tilapia (Oreochromis niloticus) is one of the most widely cultured species globally and has successfully colonized much of the world. Despite numerous studies of this exotic species, how differences in native communities mitigate the consequences of Nile tilapia invasion is unknown. Theory predicts that communities that are more diverse should be more resistant to exotic species, an effect that is referred to as "biotic resistance", but these effects are spatially dependent and organismspecific. Field surveys and laboratory experiments were conducted to test the theory of "biotic resistance" and ascertain the relationship between native species richness and the invasion of Nile tilapia. In the field, we found that as native species richness increased, the biomass of Nile tilapia was significantly reduced. Consistent with results from the field, our manipulative experiment indicated that the growth of Nile tilapia was negatively related to native species richness. Thus, our study supports the theory of "biotic resistance" and suggests that species biodiversity represents an important defense against the invasion of Nile tilapia. RÉSUMÉLa diversité des espèces protège contre l'invasion du tilapia du Nil (Oreochromis niloticus) Le tilapia du Nil (Oreochromis niloticus) est l'une des espèces les plus largement élevées à l'échelle mondiale et il a colonisé avec succès la plupart des pays. Malgré de nombreuses études de cette espèce exotique, comment les diffé-rences dans les communautés indigènes influencent les conséquences de l'invasion du tilapia du Nil est une donnée inconnue. La théorie prédit que les communautés qui sont plus variées devraient être plus résistantes aux espèces exotiques, un effet qui est dénommé « résistance au stress biotique », mais ces effets sont spatialement dépendants et propres à chaque organisme. Des études de terrain et des expériences de laboratoire ont été menées afin de tester la théorie de la « résistance au stress biotique » et de détermi-ner la relation entre la richesse des espèces indigènes et l'invasion du tilapia du Nil. Sur le terrain, nous avons constaté que, quand la richesse des espèces indigènes augmente, la biomasse du tilapia du Nil est considéra-blement réduite. Conformément aux résultats sur le terrain, notre expérience de manipulation indique que la croissance du tilapia du Nil est négativement associée à la richesse des espèces indigènes. Ainsi, notre étude confirme la théorie de la « résistance au stress biotique » et suggère que la biodiversité des espèces représente un important moyen de défense contre l'invasion du tilapia du Nil. Mots-clés :

Nile tilapia (Oreochromis niloticus) invasions disrupt the functional patterns of fish community in a large subtropical river in China

“…In China, Nile tilapia was initially introduced into Guangdong Province for aquaculture in 1957, and it has since become an important aquaculture species in the southern part of the country (Gu et al, ). However, recent evidence suggests that it has escaped aquaculture facilities and is now naturalised in the wild, and its distribution has expanded to most of the river systems in south China (Blackburn et al, ; Shuai, Li, Chen, Li, & Lek, ).…”

Fish invasion in the river systems of Guangdong Province, South China: Possible indicators of their success

“…However, the relative contribution of resident diversity to invasion resistance varies across different exotic taxa and spatial scales (Davies et al, 2010;Gu et al, 2014). Of course, this theory does not hold up well for fish invasions into streams and estuaries (Gu et al, 2014;Meador et al, 2003;Moyle & Light, 1996). This theory has been well explained in many aquatic ecosystems.…”

“…The historical data were collected when the invasive fish species had not established, and these results showed that biotic resistance was greater in the invasion process of non-native fish species. The decrease of native species caused by environmental changes, overfishing and other factors may generate large numbers of empty niches, which will accelerate the speed of invasion (Carey & Wahl, 2010;Gu et al, 2014). Sampling date and county-level administrative regions where sites were located according to the People's Government of Guangdong Province.…”

“…Many external factors influence invasion and spread of non-native aquatic species, including: (1) facilitated spread of non-native species by water diversion projects ; (2) the hydrological regime affects the distribution of the invasive fish species (Moyle & Light, 1996;Shuai et al, 2015); (3) level of human disturbance, a fluctuating environment may be one of the most important factors that favours invasion, and human disturbance is a significant influence (Linde, Izqouierdo, Moreira & Garcia-Vazouez, 2008;Meador et al, 2003). Therefore, when biodiversity decreases, the biomass and numbers of invaders increases, and this mechanism is referred to as "biotic resistance" (Davies, Cavender-Bares & Deacon, 2010; Gu et al, 2014;Kimbro, Cheng & Grosholz, 2013;Meador et al, 2003;Moyle & Light, 1996); (5) water quality assists the establishment of invasive animals, as degraded water quality may promote invasion of non-native species (Greene, McElarney & Taylor, 2015;Linde et al, 2008); (6) the local diet and the commercial value of nonnative species (Irons et al 2007;Hu et al, 2015;Gu et al, 2015); and (7) the influence of the aquaculture industry on non-native species establishment and invasion, as the number of introduction events and the annual output of the non-native fish species impact the probability of their success (Early et al, 2016;Liu & Li, 2009). Therefore, when biodiversity decreases, the biomass and numbers of invaders increases, and this mechanism is referred to as "biotic resistance" (Davies, Cavender-Bares & Deacon, 2010; Gu et al, 2014;Kimbro, Cheng & Grosholz, 2013;Meador et al, 2003;Moyle & Light, 1996); (5) water quality assists the establishment of invasive animals, as degraded water quality may promote invasion of non-native species (Greene, McElarney & Taylor, 2015;Linde et al, 2008); (6) the local diet and the commercial value of nonnative species (Irons et al 2007;Hu et al, 2015;Gu et al, 2015); and (7) the influence of the aquaculture industry on non-native species establishment and invasion, as the number of introduction events and the annual output of the non-native fish species impact the probability of their success …”

“…The ecosystem disturbance hypothesis is one of the most fundamental hypotheses in ecology, which proposes that a disturbance will promote invasion of non-native species (Diez et al, 2012;Moyle & Light, 1996;Radhakrishnan, Lan, Zhao, Qing & Huang, 2011); (4) biodiversity loss accelerates the invasion of non-native species, biotic resistance usually refers to the ability of a natural community to resist the establishment and growth of invaders. Water diversion projects have been built around China, but rarely in Guangdong Province, water temperature and the hydrological regime only vary slightly, and the hydrological regime has been discussed by Radhakrishnan et al (2011); Gu et al (2014); and Shuai et al (2015). However, environmental conditions differ in different regions, and invaders are also different.…”