Do frugivores enhance germination success of plant species? An experimental approach

Chama, Lackson; Berens, Dana G.; Downs, Colleen T.; Farwig, Nina

doi:10.1016/j.sajb.2013.05.003

Cited by 13 publications

(12 citation statements)

References 23 publications

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“…, Mokotjomela , Chama et al . ). Movement over long distances influences dispersal quality by reducing intraspecific competition and seed predation, which are generally higher close to the source (Howe & Smallwood ), by opening genetic links between disconnected plant communities (Van Der Pijl , Nathan et al .…”

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confidence: 97%

“…Benefits of avian endozoochory include dormancy release and enhanced germination (Howe & Smallwood 1982, Schupp et al 2010, especially where there is vector-specificity (Traveset et al 2001). Although germination may be enhanced by passage through a bird's gut, it may also remain unchanged or even be suppressed (Traveset 1998, LaFleur et al 2009, Jordaan et al 2011, Mokotjomela 2012, Chama et al 2013. Movement over long distances influences dispersal quality by reducing intraspecific competition and seed predation, which are generally higher close to the source (Howe & Smallwood 1982), by opening genetic links between disconnected plant communities (Van Der Pijl 1982, Nathan et al 2008, Schurr et al 2009, Schupp et al 2010) and by facilitating the formation of new self-sustaining populations in different landscapes (Sakai et al 2001, Nathan et al 2008.…”

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confidence: 99%

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The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa

Mokotjomela

Hoffmann

Downs

2015

Ibis

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Rooikrans Acacia cyclops is an aggressive invasive tree that threatens natural resources in South Africa. The seeds of A. cyclops have a prominent aril which attracts birds that ingest the seeds and disperse them endozoochorously. Two biological control agents, a Seed Weevil Melanterius servulus and a Flower‐galling Midge Dasineura dielsi, were released on A. cyclops in 1991 and 2002, respectively. Together these agents have substantially reduced seed production and generally far lower numbers of seeds are now available to birds. A consequence of this transition from historically bounteous quantities of seeds to scanty seed availability is that birds may no longer associate with the trees and seed dispersal may be disproportionately reduced. To assess whether this has happened, seed attrition was measured by comparing the amount of seeds that disappeared from two groups of branches, one available to birds and the other enclosed in bird netting. Other types of granivores (mainly field mice) were excluded from both groups of branches with a plastic funnel placed around the stems. Mature seeds were also harvested and fed to caged bird species to determine gut retention times and germination rates of ingested seeds. Attrition rates of seeds showed that birds continue to remove seeds but that only a proportion of the crop is taken. Only two frugivorous species (Knysna Turaco Tauraco corythaix and Red‐winged Starling Onychognathus morio) and two granivorous species (Red‐eyed Dove Streptopelia semitorquata and Laughing Dove Streptopelia sengalensis) ingested A. cyclops seeds during feeding trials. Ingestion by birds enhanced seed germination except for those ingested by Laughing Doves. There were no apparent effects of length of gut passage time and avian body size on seed germination rates. Despite the diminished seed resource due to biological control agents, birds continue to disperse A. cyclops seeds.

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confidence: 97%

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confidence: 99%

The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa

Mokotjomela

Hoffmann

Downs

2015

Ibis

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“…In addition, Z. mucronata has a high seed viability of up to 100% (Weiersbye and Witkowski, 2002) and a high physiological plasticity in a broad variety of environmental conditions (Refka et al, 2013;Zietsman and Botha, 1987). An unchanged germination of bird-ingested seeds has been previously reported in South Africa (Mokotjomela et al, 2015;Chama et al, 2013;Mokotjomela, 2012;Jordaan et al, 2011), which highlights, in this context, the role of birds in transporting seeds to new microsites. Wenny (2000) also found that both the seeds ingested by birds and those manually depulped germinated equally well (98%) for Ocotea endresiana (Lauraceae).…”

Section: Germination Trials: Bird-ingested Vs Depulped Seedsmentioning

confidence: 77%

Interspecific competition in germination of bird-dispersed seeds in a habitat with sparse tree vegetation in South Africa

Mokotjomela

Vukeya

Malebo

et al. 2020

Preprint

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Avian frugivores provide directed seed dispersal services that contribute in shaping the native plant communities and facilitate population persistence. By transporting and scarifying the seeds during ingestion, avian frugivores reduce the competition with siblings, and may improve the germination which is critical for dispersal effectiveness. However, generally, there is limited knowledge on how deposited seeds interact/compete in the new microsite. Therefore, we investigated 1) whether bird-dispersed seeds benefit from improved germination after their passage through the bird’s gut; and 2) the potential impact of seed density on competition at the microsites by determining whether seed density and species diversity influence germination in the Free State Province, South Africa. Overall, the results partly supported the hypothesis. Germination trials with defecated seeds of five plant species compared with the manually depulped seeds showed that despite prolific seed germination observed in Ziziphus mucronata, only Searsia lancea seeds had significantly high seed germination after passage through the bird gut. Overall, there was a significant correlation between seed size and the germination of bird-ingested seeds except in Olea subsp. africana possibly due to possession of extremely hard protective seed cover. Seeds competition experiments pointed to Z. mucronata and O. subsp. africana having significant germination performance that was positively correlated to seed density and seed size while E. rigida did not germinate at all. Seed species diversity in the germination trays did not have significant impact since only two former plant species consistently displayed significantly higher germination across the competition levels. We conclude that not all bird-defecated seeds have their germination improved, and that further long-term tests for germination physiological responses of the seeds’ samples used in this study are required since poor germination observed in other tree/shrub species cannot be attributed to competition solely.

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“…Where forest fragments do possess a high amount of fruit availability, they can be instrumental in maintaining the connectivity of forest fragments and patches in a matrix, if the forest community is one tolerant of fragmentation (Berens et al 2014). This resource availability is a crucial determinant in the health of the plant-frugivore network (Chama et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Atlas data indicate forest dependent bird species declines in South Africa

Cooper

Wannenburgh²,

Cherry

2017

Bird Conservation International

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SummaryForest ecosystems in South Africa are at risk from a variety of anthropogenic threats impacting the faunal species dependent on them. These impacts often differ depending on species-specific characteristics. Range data on forest dependent bird species from the South African Bird Atlas Project (SABAP1 and SABAP2) were analysed to determine links between deforestation, species characteristics and range declines. Half of the species studied were found to have declining ranges. Range change data for these species were correlated with data on changes in land cover from 1990 to 2014. To determine which land cover changes affect extinction, occupancy was modelled for 30 sites across South Africa which experienced a loss of more than 10 species. Most species lost were birds of prey or insectivores. Indigenous forest decreased in 17% (n = 5) sites, while plantations/woodlots decreased in 60% (n = 18) sites. Occupancy modelling showed extinction to be mitigated by plantations in 6/28 species, and forest expansion mitigated extinction in 7/28 species. Responses to deforestation did not appear to be related to particular species characteristics. Half of South Africa’s forest-dependent bird species have declining ranges, with the loss of these species most prominent in the Eastern Cape province. Four responses to changes in forest and plantation cover are discussed: direct effects, with forest loss causing species loss; matrix effects, where plantation loss resulted in species loss; degradation of indigenous forest; and the advent of new forest arising from woody thickening caused by carbon fertilisation, which may not result in optimal habitat for forest-dependent birds.

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Do frugivores enhance germination success of plant species? An experimental approach

Cited by 13 publications

References 23 publications

The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa

The potential for birds to disperse the seeds of Acacia cyclops, an invasive alien plant in South Africa

Interspecific competition in germination of bird-dispersed seeds in a habitat with sparse tree vegetation in South Africa

Atlas data indicate forest dependent bird species declines in South Africa

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