Implications of newly-formed seed-dispersal mutualisms between birds and introduced plants in northern California, USA

Abstract

I examined the role of bird dispersal in invasiveness of three non-native plant species in California, USA: Triadica sebifera, Ligustrum lucidum, and Olea europaea. I selected these species because their invasiveness in California is uncertain, but a survey of ornithologists highlighted them as likely bird-dispersed. I quantified bird frugivory of these plants, compared them with a native species (Heteromeles arbutifolia), and explored the management implications of dispersal mutualisms for these and other incipient invasive plants. Fruit removal by birds was sufficient to permit spread for all study species. Seed dispersers (rather than seed predators) and pulse feeders (flocking species with potential for long distance dispersal) performed most fruit removal for the non-native species, a pattern indicative of an effective dispersal regime. The number of fruiting trees per stand was a significant predictor of bird visitation. Founding population size may thus be important in management of invasive, bird-dispersed plants. Disperser-defined niches were relatively narrow because a few disperser species performed the majority of fruit removal from study trees, but each fruit species was consumed by a variety of potential dispersers. This results in strong pairwise niche overlap between some plant species. Ordinated by bird use, study site-species combinations clustered more by geographic location than by plant species, emphasizing the opportunistic nature of bird foraging. None of the non-native focal plant species appears dispersal limited, and all have formed novel mutualisms in California. It is possible that these plants are now in lag phases preceding bird-mediated invasion. Consideration of bird dispersal when evaluating invasiveness is therefore an imperative.

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…Since evidence suggests that neighborhood effects in interspecific neighborhoods are likely to be facilitative (Carlo et al, 2007), the introduction of plants may increase fruit removal of neighbors (Gleditsch and Carlo, 2010; Figure 2A). However, competition for dispersers can also occur (Aslan, 2011;Spotswood et al, 2012). Introduced plants can change habitat structure, thereby influencing disperser foraging behaviors (Traveset and Richardson, 2006).…”

Mutualism risky in the suburban area: fruits of exotic tree Schefflera actinophylla (Endil.) Harms (Araliaceae) benefit native birds that potentially disperse their seeds

“…Porém, isso não implica menores preocupações com relação à Schefflera actinophylla. Muitas espécies exóticas podem persistir de forma latente no ambiente, tornando-se invasoras na medida em que o tempo de persistência avança (ELTON, 1958;HOBBS;HUMPHRIES, 1995;ASLAN, 2011). Além disso, há evidências que indicam riscos de invasão por S. actinophylla em regiões brasileiras.…”

“…Além disso, há evidências que indicam riscos de invasão por S. actinophylla em regiões brasileiras. Essa espécie tem características típicas de espécies invasoras, ou seja, estendida e prolífica produção de pequenos frutos rico em sementes, facilmente acessados pelas aves generalistas quanto aos tipos de hábitats, que, comprovadamente, facilitam invasões de plantas exóticas via dispersão de sementes (ELTON, 1958;RICHARDSON et al, 2000b;MILTON et al, 2007;ASLAN;REIMÁNEK, 2010;ASLAN et al 2012 (GUCKER, 2011).…”

“…As áreas urbanizadas das cidades brasileiras são bons exemplos de um ambiente rico em espécies exóticas, já que a arborização dessas localidades é composta, sobretudo, por espécies exóticas (PIRES et al, 2007;SANTOS et al, 2010;MORO et al, 2014), algumas das quais invasoras, trazidas de outros países para serem cultivadas como ornamentais (MORO et al, 2013). Parte das plantas introduzidas como ornamentais se tornam invasoras na nova região geográfica e algumas delas interagem com aves nativas que se alimentam de seus frutos e dispersam suas sementes (RICHARDSON et al, 2000b;REICHARD et al, 2001;CORLETT, 2005;GUIX, 2007;ASLAN;REJMÁNEK, 2010;ASLAN, 2011;ASLAN et al, 2012;MUNÕZ;ACKERMAN, 2013). Caso as sementes sejam dispersas para um ambiente favorável, a espécie pode ter sucesso reprodutivo (sensu HOWE;SMALLWOOD, 1982;RICHARDSON et al, 2000b).…”

Pine Stand Density Influences the Regeneration of Acacia saligna Labill. H.L.Wendl. and Native Woody Species in a Mediterranean Coastal Pine Plantation

“…Previous regeneration data obtained from field investigations carried out in the same protected area suggest that Olea has experienced a marked increase in the last 10-15 years [41]. Such a sizable change may be due to an increase in the effective seed dispersal by birds and to possible shifts in their natural population [59]. Conversely, Pistacia showed a much lower regeneration density (mean: 5,700 N ha −1 ), with non-significant variations based on the stand density.…”