Browsing by Author "Soares, Filipa Coutinho"
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- Combined effects of bird extinctions and introductions in oceanic islands: Decreased functional diversity despite increased species richnessPublication . Soares, Filipa Coutinho; F. De Lima, Ricardo; M. Palmeirim, Jorge; Cardoso, Pedro; Rodrigues, Ana S. L.; Pigot, Alex L.Aim We analyse the consequences of species extinctions and introductions on the functional diversity and composition of island bird assemblages. Specifically, we ask if introduced species have compensated the functional loss resulting from species extinctions. Location Seventy-four oceanic islands (> 100 km2) in the Atlantic, Pacific and Indian Oceans. Time period Late Holocene. Major taxa studied Terrestrial and freshwater bird species. Methods We compiled a species list per island (extinct and extant, native and introduced), and then compiled traits per species. We used single-trait analyses to assess the effects of past species extinctions and introductions on functional composition. Then, we used probabilistic hypervolumes in trait space to calculate functional richness and evenness of original versus present avifaunas of each island (and net change), and to estimate how functionally unique are extinct and introduced species on each island. Results The net effects of extinctions and introductions were: an increase in average species richness per island (alpha diversity), yet a decline in diversity across all islands (gamma diversity); an average increase in the prevalence of most functional traits, yet an average decline in functional richness and evenness, associated with the fact that extinct species were functionally more unique (when compared to extant natives) than introduced species. Main conclusions Introduced species are on average offsetting (and even surpassing) the losses of extinct species per island in terms of species richness, and they are increasing the prevalence of most functional traits. However, they are not compensating for the loss of functional richness due to extinctions. Current island bird assemblages are becoming functionally poorer, having lost unique species and being composed of functionally more redundant species. This is likely to have cascading repercussions on the functioning of island ecosystems. We highlight that taxonomic and functional biodiversity should be assessed simultaneously to understand the global impacts of human activities.
- Effects of bird extinctions and introductions on the functional and taxonomic diversity of oceanic islandsPublication . Soares, Filipa Coutinho; Lima, Ricardo Faustino de; Palmeirim, Jorge Manuel Mestre Marques; Rodrigues, Ana Sofia LuísHuman activities are causing major changes in the composition of species communities worldwide. Oceanic islands are at the epicentre of these changes, being among the most threatened ecosystems. Drastic changes in island bird communities resulting from both species extinctions and introductions are likely to have important repercussions on the composition and function of island avifaunas, potentially causing severe knock-on effects on island ecosystems. The main objective of this thesis was to explore the taxonomic and functional implications of bird extinctions and introductions for the avifauna of oceanic islands worldwide. It focuses on large oceanic islands (> 100 km2; n = 74), distributed across three oceans. Using island lists of extinct and extant, native and introduced species, plus species functional traits and island characteristics, the thesis first addresses the potential competition between native and introduced island bird species. Then, it evaluates the impacts of bird extinctions and introductions on island functional diversity, investigating island-level consequences, taxonomic and functional homogenization among archipelagos, and patterns and drivers of spatial and temporal taxonomic and functional changes. Overall, the results suggest that marked niche differentiations between native and introduced birds explain the apparent rarity of competition-driven extinctions. Similarly, introduced birds differ from extinct birds because they mostly prefer human-modified landscapes, which might explain why they do not compensate for the lost functional diversity due to extinctions. Island bird assemblages are becoming functionally poorer because they are losing unique species while gaining widespread functionally more redundant species, and therefore are becoming taxonomically and functionally homogenized. Anthropogenic pressure and human connectivity are driving the taxonomic and functional changes across oceanic islands. Assessing temporal changes in taxonomic and functional diversity is key to understand anthropogenic impacts, predict future changes and propose effective conservation tools to safeguard the resilience of ecosystem functioning.