Network structure of estuarine food webs: the role of humans and climate change Catarina 1MARE
1* Vinagre ,
Maria J.
1 Costa ,
Spencer A.
2 Wood ,
Richard J.
3 Williams ,
Jennifer A.
4 Dunne
– Marine and Environmental Sciences Centre; Faculdade de Ciências da Universidade de Lisboa, Portugal; 2Department of Zoology, University
of British Columbia, Vancouver, BC, Canada; 3Microsoft Research, Cambridge CB3 0FB, United Kingdom; 4Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501, USA.
- Tagus estuary (Portugal) food web -
*
[email protected]
Red – humans Blue – other vertebrates Yellow – invertebrates Orange – parasites Green – photosynthetic species (grouped) Black – lost species in the past; new species in the present and future
Past (1978-1981)
Platichthys flesus European flounder
3 cold-water species lost Ciliata mustela Fivebeard rockling
Sprattus sprattus Sprat
Present (2000-2002) • A ‘‘Climate envelope’’ model was developed in a +2ºC (SST) scenario (IPCC A2). • The current distribution of species was mapped in climate spaces, and species composition was changed according to the predicted latitudinal changes of those climate spaces.
7 new species, Not detected in 1978-1981
• Three structural food web networks were assembled (based on published works that cover the whole Tagus estuary and on the results from the climate envelope model). • Network structural food webs depict “who eats whom”. • 15 network properties (e.g. species richness, links per species, conectance; normalized standard deviation of links; mean shortweighted trophic level, % top species, % cannibalism, etc) were compared among the three food webs.
Future (2100)
Milk shark (Rizoprionodon acutus)
• The ability of the niche model and the probabilistic niche model (PNM) to predict food web properties was compared for each estuarine food web. Past
Present
Future
1978-1981
2000-2002
2100
Sprattus sprattus
1
0
0
Ciliata mustela
1
0
0
Platichthys flesus
1
0
0
Eriocheir sinensis
0
1
1
Raja clavata
0
1
1
Halobratrachus didactylus
0
1
1
Argyrosomus regius
0
1
1
Sparus aurata
0
1
1
Diplodus bellottii
0
1
1
Arnoglossus laterna
0
1
1
Rhizoprionodon acutus
0
0
1
Trachurus trecae
0
0
1
Ethmalosa fimbriata
0
0
1
Pseudotolithus senegalensis
0
0
1
Pseudotolithus typus
0
0
1
Pseudopneus prayensis
0
0
1
Callionymus risso
0
0
1
Mugil capurri
0
0
1
Brachydeuterus auritus
0
0
1
Species
0 – species lost 1 – species added (or present in the past)
Acknowledgments This study had the support of the Portuguese Foundation for Science and Technology through the grant SFRH/BPD/34934/2007 awarded to C. Vinagre, the projects PTDC/AAG-REC/2139/2012 and PTDC/MAREST/2141/2012 and the strategic project PEst-OE/MAR/UI0199/2011 granted to Centro de Oceanografia (MARE).
9 new species, From warmer waters
Conclusions: • The species alteration did not change the basic network properties of the Tagus estuary food web. • The addition of 16% new nodes did not impact overall structure in terms of niche model fit and PNM fit. Because more species will be added than lost, there will be an increase in species richness. • The role of humans, as the top predators with the most prey links, will be reinforced in the future since many of the new species are commercial species. • The addition of a medium size shark (1,75 m), the milk-shark, may have an impact since it feeds on the most important commercial species. This shark has predators, larger sharks, in the tropical areas where it occurs. However, these larger sharks are not expected to colonize the Portuguese coast. • This means that a highly generalist species, potentially with no predators has the potential to colonize the Portuguese coasts and its estuaries. For more information go to http://webpages.fc.ul.pt/~cmvinagre
