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More young and other traits help mam­mals adapt to urban environments

pub­lished 24 Decem­ber 2018 | mod­i­fied 24 Decem­ber 2018

Hedgehog near colosseo RomeMam­mal species that live in urban envi­ron­ments pro­duce more young com­pared to other mam­mals. But next to this com­mon ‘win­ning trait’, mam­mals deal with dif­fer­ent strate­gies to suc­cess­fully inhabit cities. This is what Rad­boud Uni­ver­sity ecol­o­gist Luca San­tini and col­leagues found in a study that is pub­lished on 21 Decem­ber in Ecol­ogy Let­ters. “This is the first step of many to under­stand why cer­tain mam­mals man­age to live in cities and why other species don’t.”

Mam­mals liv­ing in urban envi­ron­ments tend to be more of a nui­sance to human inhab­i­tants than birds, because they are often regarded as pests – for exam­ple rats and bats – and dam­age struc­tures or goods, as wild boars do. “It’s impor­tant to gain more insight into how mam­mals live in urban envi­ron­ments, so we can even­tu­ally achieve a more peace­ful coex­is­tence,” San­tini says.

Traits that ben­e­fit urban mam­mals
San­tini and col­leagues col­lected stud­ies from all over the world that recorded the num­ber of mam­mal species in cities. “The large num­ber of stud­ies that have already been con­ducted show that birds in cities, for exam­ple crows, tend to be more clever, mean­ing that they are bet­ter able to adapt to unex­pected sit­u­a­tions. How­ever, mam­mals in cities are far less inves­ti­gated, and only stud­ies on a sin­gle mam­mal species, such as bats, have been car­ried out.

Mam­mals have way more diverse traits than birds, such as a higher diver­sity in body struc­ture, size, life-​history and ecol­ogy. There­fore, we were curi­ous to know whether there are par­tic­u­lar traits that are pos­i­tively affect­ing the abil­ity of mam­mal species to flour­ish in new ecosys­tems, such as urban environments.”

Larger lit­ters, brains and bod­ies
The find­ing that stands out most is that all groups of urban mam­mals seem to pro­duce more young. San­tini explains:

In gen­eral, ani­mals that pro­duce larger lit­ters do so to com­pen­sate for a high mor­tal­ity rate amongst their young. This sug­gests that a high mor­tal­ity rate due to, for exam­ple, road traf­fic acci­dents, per­se­cu­tion by humans, and pre­da­tion by domes­tic cats and dogs could be a major selec­tive pres­sure for mam­mals in urban environments.

Luca San­tini, lead author, Depart­ment of Envi­ron­men­tal Sci­ence, Insti­tute of Water and Wet­land Research, Rad­boud Uni­ver­sity, Nijmegen, The Netherlands

Dif­fer­ences in other traits were less explicit. “For exam­ple a larger brain mass appears to be mostly asso­ci­ated with car­ni­vores and pri­mates who only occa­sion­ally visit urban envi­ron­ments, such as jack­als, wolves, bears and baboons, rather than with mam­mals who per­ma­nently live in cities, such as genet cats and mon­gooses among car­ni­vores, or hedge­hogs and shrews among insec­ti­vores. We also found that car­ni­vores and pri­mates that spo­rad­i­cally visit cities tend to be larger than aver­age. This may be because they need to cover large dis­tances in short times.”

mammals in urban environmentNum­bers of mam­mal species per order found in urban envi­ron­ments. Num­bers in paren­the­ses indi­cate per­cent­age of urban species within the order. The visitors/​dwellers cat­e­gory reflects species that due to ambigu­ous evi­dence from the lit­er­a­ture were included as vis­i­tors and as dwellers in the analy­ses.
Luca San­tini et al., 2018. One strat­egy does not fit all: deter­mi­nants of urban adap­ta­tion in mam­mals. Ecol­ogy Let­ters.
Open access arti­cle under the terms of the Cre­ative Com­mons Attri­bu­tion License.

Dif­fer­ent strate­gies for dif­fer­ent species
Over­all, the results indi­cate that dif­fer­ent groups of mam­mals use dif­fer­ent strate­gies to deal with the urban envi­ron­ment. “How­ever, because the num­ber of mam­mal species in an urban envi­ron­ments com­pared to the total num­ber of mam­mal species is quite small – 190 out of approx­i­mately 6,000 species – this makes the sta­tis­tics quite chal­leng­ing, con­se­quently it is hard to make def­i­nite state­ments about spe­cific groups of mam­mals and traits.”

San­tini hopes to inves­ti­gate fur­ther ques­tions in the future, such as which species live in parks, sub­urbs or city cen­tres and why. “We expect that the num­ber of ani­mals liv­ing in urban envi­ron­ments will increase, because urban areas will expand and nat­ural habi­tat will become more frag­mented. Many ani­mals that we believe can­not live in urban areas today, might start vis­it­ing and using cities in the future.”

(Source: Rad­boud Uni­ver­sity news release, 21.12.2018)

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