Recent changes in plant and animal distribution in the southern extreme of the Paranaense biogeographical province ( northeastern Buenos Aires province , Argentina ) : Ecological responses to climate change ?

The Northern region of Buenos Aires province, in Argentina, suffered an uninterrupted increase in rainfall and temperature values during the last decades. The aim of the present contribution is to analyze the effects of such climatic change in the distribution of local flora and fauna. The analysis resulted in the recognition of distributional shifts in a total of 115 species. These changes represented the progressive southern expansion of species typically present in subtropical areas. Because all these changes have a similar orientation and direction, and included a large number of plant and animals with different ecological requirements, it is here postulated that those geographical changes are probably a response to climatic alteration.

In spite of that, an integrative study about the impacts of recent climate change on Argentinean ecosystems is still lacking.Studies about changes in species geographical distribution related to climatic variation were mainly conducted in mammals (e.g.Udrizar Sauthier et al., 2005;Fracassi et al., 2010), medically important snakes (Nori et al., 2013), insects (Farina, 2006;Medone et al., 2015), and arachnids (Guerrero, 2014a).Furthermore, there is a single phenological study of changes in arriving times of a migratory swallow (Spescha et al., 2004).Nevertheless, each one of these works focus on single species or on a small taxonomic group of animals.On the other hand, plant species range shifts deserved almost no attention.The aim of this paper is twofold: first, to show that geographical changes in species are not isolated and that there is a common tendency to extend the southern limit of subtropical plant and animal species; and second: to examine if the observed shifts on animal and plant species distribution could be attributed to climatic change.

Geographical settings
We analyzed the northeastern sector of Buenos Aires province, where Paranaense riparian forests have their southernmost patches along the coast of the Lower Paraná and La Plata rivers (Figure 2).We restricted our research to this area because it was largely considered as the best known region in Argentina from a biological viewpoint, and because it was the focus of study of several researchers during the 19 th and 20 th centuries.Consequently, large biological collections are available from this area since historical times.This allows comparison between old and recent collections.We did not include central and southern Buenos Aires province, even though some recent cases of shifts on animal species distributions were probably caused by climate change (e.g.Zamorano & Scillato-Yané, 2008;Doumecq-Milieu et al., 2012).This is because those areas were poorly sampled by researchers in historical times.
From north to southeast, Pergamino, San Nicolás, Ramallo, San Pedro, Baradero, Zárate, Campana, Pilar, Zelaya, Tigre and San Isidro districts, together with Martín García Island   Guerrero & Agnolin: Recent changes in plant and animal distribution encompasse the northern boundary of Buenos Aires province, including Paraná's Delta and slope talares; from Buenos Aires City to the southeast are located the districts of Avellaneda, Quilmes, Berazategui, Ensenada, La Plata, Berisso, Magdalena and Punta Indio; Punta Lara Natural Reserve is placed between Berazategui and Ensenada districts, and Parque Costero del Sur Natural Reserve in Magdalena and Punta Indio districts.

Taxon selection
Analyzed taxa were chosen under two main criteria.Firstly, we selected relatively well-studied species from the biogeographical point of view.On the other hand, we analyzed if a comparison between old and recent researches was possible.Consequently, we analyzed selected vascular plants, harvestmen (Arachnida, Opiliones), spiders (Arachnida, Araneae), Rhopalocera butterflies (Insecta, Lepidoptera), and some vertebrates, including birds (Aves), chelonians (Testudines), and mammals (Mammalia).Present paper is based on an exhaustive review of published literature and our own research.Distributional areas in each case were determined from bibliographical data such as catalogues and reviews.Below is a brief review of the bibliography and collections we examined for each group: Vascular plant distribution.The oldest wellreferenced collections from La Plata River coast are those of John Tweedie (between 1825 and 1832) and Carlos L. Spegazzini (in 1880 decade).Nikolai M. Alboff, Carlos Berg, Lucien Hauman, Cristóbal Hicken, and many others collected a big amount of specimens in the area by the late 19 th and early 20 th centuries.Collections and works on the provincial flora increased quickly, and the monumental work "Flora de la provincia de Buenos Aires", directed by Ángel L. Cabrera (1963Cabrera ( -1970) ) summarized the knowledge of plant species distribution in this province up to that date.Therefore this document became the basis for any further study, including the present contribution.Additional data was achieved from specialized works, especially about ferns (e.g.Capurro, 1961).
Arachnida distribution.We included in this item the clades Opiliones and Araneae.Opiliones in Argentina were studied in great detail by Raúl A. Ringuelet.Analyses of Ringuelet´s monograph about Argentinean species of the clade (1959) shows that northeastern Buenos Aires province is the area with most previous collection sites, probably due to its proximity to Buenos Aires and La Plata natural science mu-seums (Acosta, 2014).Therefore, we infer that knowledge of haverstmen in this area is relatively good.Furthermore, in this part of the province several harvestmen that distribute along the Argentinean Mesopotamia (the geographical area encompassed between Paraná and Uruguay rivers) have their southern limit of geographical distribution (Ringuelet, 1959;Acosta, 2002).On the contrary, because the Araneae are not well studied on a zoogeographical point of view, only a brief analysis of two well-studied genera is added.
Lepidoptera distribution.Lepidoptera species were shown to be very useful in climatic change studies, with many responses to that phenomenon (Kocsis & Hufnagel, 2011).During the last decade, butterfly communities in northeastern Buenos Aires province were analyzed in detail in some sparse localities (Núñez Bustos, 2007, 2008, 2009;Núñez Bustos et al., 2013).However, well-sampled old lepidopteran collections were made by researchers by late 19 th and early 20 th centuries (Breyer, 1939b;Hayward, 1973;Canals, 2000).In this way, it is possible to made useful comparisons between old collections and recent observations.When Hayward's comprehensive catalogue ( 1973) is compared with recent works (Canals, 2000;Núñez Bustos, 2007;2008;2009;Núñez Bustos et al., 2013), a significant number of species were added recently to Buenos Aires fauna.
Bird distribution.The avifauna of Buenos Aires city and neighboring region was studied by the late 19 th century by several authors (d 'Orbigny, 1847;Burmeister, 1868;Lynch Arribálzaga, 1878;Holmberg, 1878Holmberg, , 1898;;Sclater & Hudson, 1888;Narosky & Gallegos, 1992), and since then, this coastal zone has been considered as the best known area of Argentina from the ornithological point of view.Later works, like those of Olrog (1963Olrog ( , 1979) ) and Narosky & Di Giacomo (1993) allow good comparisons and recognition of main distributional patterns.
Chelonia distribution.Knowledge of the distribution of reptiles and amphibians in the northeastern sector of Buenos Aires province is still patchy and biased.Among them, it is possible that the best known group are the turtles, probably because they are easy to observe and identify.Furthermore, as indicated by Crick & Sparks (1999), the turtles are very sensitive and climate-affected taxa, mainly because their nestling is climate-driven.Information on geographic distribution of chelonians was taken from the exhaustive papers by Freiberg (1977), Gallardo (1977), andCabrera (1998).
Mammalia distribution.Small mammals, especially rodent, have been found as valuable sources indicative of climate regime (Cameron & Scheel, 2001).In Argentina, most studies regarding detailed distribution and taxonomy of smallmammals were carried out by the relatively recent efforts of Elio Massoia by the 1960 decade.An important contribution is that of Galliari et al. (1991), which stands as the main compilation of mammalian records of the province up to that date.Since then, the studies on micromammal assemblages in Buenos Aires have been greatly increased (e.g., Udrizar Sauthier et al., 2005;Teta et al., 2010Teta et al., , 2014;;Pardiñas et al., 2010), but unfortunately species distribution in Buenos Aires province is still far from being well-understood.Therefore, we focus our work on middle mammals, which are well represented in public collections, they are usually well known by hunters, and are mentioned in 19 th century explorers' books.

Changes in vascular plants distribution
A total of 44 distribution changes in vascular plant species was confirmed (Table 1).
Many novel species records are here made for the first time in the Punta Lara gallery rainforest.First explorations to this Natural Reserve were made by Nicolás M. Alboff, Carlos L. Spegazzini and Lucien Hauman by the late 19 th and early 20 th centuries.Later, Ángel L. Cabrera and collaborators studied extensively this rainforest between 1926 and 1944 (Cabrera & Dawson, 1944).Plant collections in that place did not stop after that, and late to Cabrera & Dawson's work, new information was available during the preparation of the "Flora de la provincial de Buenos Aires" (Cabrera, 1963(Cabrera, -1970)).More recently, the exhaustive efforts of Flavio Moschione (1987Moschione ( , 1992) ) and Moschione & Klimaitis (1988) resulted in the addition of 17 new records of native plant species to Punta Lara's flora.Finally, Giudice et al. (2011) collected other three fern species not previously found in that locality.The works commented here were conducted in the same 6.6 hectares of the Punta Lara Natural Reserve.It is surprising that after 100 years of botanical research in this relatively small area, the increase in species richness did not reach the asymptote.
The progressive enrichment of the flora in this region, as noted by the above mentioned authors, is due to the conquest of plants from more northern locations.The "bugre", Lonchocarpus nitidus, is a particular case.In Buenos Aires province it grows in the lower Paraná Delta, Martín García Island, Avellaneda and Quilmes districts, and has its southernmost populations in the Punta Lara Natural Reserve.This legume tree is one of the most important components of Punta Lara riparian rainforest (e.g.Cabrera & Dawson, 1944;Dascanio & Ricci, 1988) and Martín García Island forest (Arturi & Juárez, 1997).However, it is curious that there are no collected specimen from there or any another part of the province up to 1925 (Paraná Delta, 1925, collected by A. C. Scala, deposited in LP herbarium).Because the species grows in an area that was visited several times by botanists during the end of the 19 th and early 20 th centuries, it is unlikely that this big ornamental plant was overlooked in the Punta Lara forest.Its distributional shift may have occurred at the end of 19 th century, and represents an example of early distributional expansion.

Changes in plant communities distribution
Leaving aside individual species range extensions, an expansion of the entire Paranaense coastal woods is documented.When comparing the southern limit of this plant community as observed by Vervoorst (1967) with today limit, we realize this wood advanced more than 25 kilometers to the south, from Salvador Grande Point to the northern limit of Samborombón Bay (both sites in Parque Costero del Sur Natural Reserve, Punta Indio district).In this regard, lineal patches of a coastal forests are present in a beach ridge between 35º 30,219' S -57º 9,795' W and 35º 30,447' S -57º 10,019' W (Figures 2  and 3).There, the characteristic tree Erythrina crista-galli is associated with Acacia caven, Sesbania punicea, S. virgata, Senna corymbo- It is also worth mentioning that several humid forests within the Parque Costero del Sur Natural Reserve may have appeared within the area during the 20 th century, as inferred from sedimentary evidence (Guerrero, 2014a).In fact, there is a fine sand stratum of about one meter thick carrying human solid waste under the soil where the forest grow up, and in some places a thin mud stratum with plastic fragments underlies the previous one (Figure 4).On this basis, it was concluded that the forests obviously grew up after these strata have settled down, and the presence of plastics within the sediment indicates they were deposited during the 20 th century (Guerrero, 2014a).

Changes in Arachnida distribution
Table 2 summarizes taxa with recent extensions on their geographical distributional area.
A total of 6 harvestmen (Opiliones) species have increased their distributional range from north to south along the La Plata River fluvial system: Discocyrtus prospicuus, Discocyrtus testudineus, Gryne orensis, Hernandaria scabricula, Metalibitia argentina and Varinodulia insularis.The southward expansion of Mesopotamian harvestmen species is strikingly coincident with the increase of rainfall and temperature in Buenos Aires province (Guerrero, 2014a).This distributional change was proposed as a climatedriven phenomenon that produced first geomorphological modifications, then physiognomic changes in the flora, and finaly harvestmen colonization (Guerrero, 2014a).
Among spiders, we recognize distributional changes in Nephila clavipes and Neotrops pombero.The first one is a good example of a recent southward expansion.This subtropical spider reached Corrientes province as its southern limit up to the 2000s, but to present time occurs on almost every humid coastal wood from Paraná Delta to Punta Indio district (Guerrero et al., 2012).Dispersion of Nephila clavipes was related to a flood event that swept some spiders downstream to north Buenos Aires.Neotrops pombero is a common species in northeastern Argentina and Paraguay (Grismado & Ramírez, 2013).Its sudden appearance in Costanera Sur Ecological Reserve in 2011 was attributed to a recent dispersal (Grismado & Ramírez, 2013;Zapata & Grismado, 2015).Many other spider species may have reached the study area in the last decades, but unfortunately lot of research is needed (Zapata & Grismado, 2015).For example, Micrathena furva (Keyserling 1892) was recorded by Levi (1985) up to Punta Lara Natural Reserve, but nowadays it extends southwards to Parque Costero del Sur Natural Reserve (Arachnological collection of La Plata Museum, La Plata, Buenos Aires, Argentina: MLP_Ar 19407).

Changes in lepidopteran distribution
Southward expansions were detected in butterfly species from different localities at Buenos Aires province.33 taxa were found as having important distributional changes (Table 3).Morpho epistropheus argentinus, considered the national butterfly due to its beauty, is a big and conspicuous species on its adult and larval stages.Farina (2006) followed the increase of its range extension across the eastern part of the province between 1985 and 2003.Up to 1939 the species was known from a few localities of northern Buenos Aires province, its southern limit being at Punta Lara (Breyer, 1939a).To early 2000s it expanded its range to Punta Piedras (Punta Indio district) and General Madariaga district (Klimaitis, 2000).Finally, a few years later it was detected in the southern General Pueyrredón district (Farina, 2006).As its favorite host plant, Scutia buxifolia (Rhamnaceae), exists in the xerophitic woods or "talares" almost since the beginnings of the 20 th century (Parodi, 1940), Farina (2006) concluded that the range expansion of this butterfly could be connected with the climatic change.Also, Hypanartia bella, Doxocopa laurentia laurentia, Phoebis neocypris, and P. sennae marcelina showed the same pattern of southward extension through the "talares" (Farina, 2006).
Another remarkable case is Adelpha syma, of which the original distribution encompasses southeastern Brazil, Uruguay, Paraguay and northeastern Argentina, was not reported in Buenos Aires province prior to the 2000s (Hayward, 1973;Willmott, 2003).Klimaitis (2000) argued the species arrived to the area due to passive raft dispersal downstream the Paraná or Uruguay rivers or by active dispersal along the Atlantic coast.Nowadays it is a common butterfly in several sites of northeastern Buenos Aires province (Núñez Bustos et al., 2013).
Finally, some species increased their abundance during the last decades.For example, Núñez Bustos et al. (2013) mention that Badecla argentinensis, which had scarce past records in Buenos Aires, became much more frequent in recent decades.

Changes in chelonian distribution
As a result of comparing old works with recent papers and observations, we found that three turtle species changed their geographical distribution and expanded its geonemy (Table 4).
The case of the Red eared slider Trachemys dorbignyi merits some explanatory comments.This species is frequent in northeastern Argentina, north to Entre Ríos province (Barco & Larriera, 1991;Richard & De La Fuente, 1992;Cabrera, 1998).Freiberg (1977; probably based on Marelli, 1924) mentioned its presence in Buenos Aires, but this report was not based on actual specimens and was considered as dubious (Richard & De La Fuente, 1992;Cei, 1993;Alcalde et al., 2012).Consequently, Williams (1991) did not include the species within Buenos Aires herpetofauna, a criterion followed by many authors.In the last decade this turtle was found in several localities of northern Buenos Aires province: San Isidro and Campana districts, and Buenos Aires city (Pereira & Haene, 2003;Chebez, 2009;Agnolin et al., 2014), possibly Punta Lara (Saibene et al., 2012), and in Magdalena, which constitutes its current southernmost locality (Alcalde et al., 2012).Thus, we consider these records corroborate the hypothesis of a geographical expansion in this species.
Hydromedusa tectifera was recently found in Sierra de La Ventana, 495 kilometers south of its previously known geographic distribution (Di Pietro et al., 2012).We did not include this record here because it is unclear if it is due to a recent natural expansion or human introduction.However, the new record here reported at Punta Indio district (Arroyo Salvador Grande, near the bridge of Route 11, 7 January 2009) may be an evidence of a natural southward expansion of the species following La Plata River coast.

Changes in bird distribution
Several authors considered that some bird species inhabiting the La Plata River coast expanded their southern distribution in recent times (Haene, 2006;Chimento et al., 2011;Godoy et al., 2012;Agnolin & Rivero, 2014).Based on available data, at least 24 different species of birds can be considered as being more widely distributed than previously known (Table 5).
We include below a brief account of some remarkable species that, according to current records, habits, and visibility, are known to have expanded its geographical distribution southwards.
The Woodpecker Melanerpes cactorum was first reported for the province in the locality of Ramallo (Maugeri & Montenegro, 2002).Recently, Chimento et al. (2009) reported for the first time that this species nests in La Plata city, 250 kilometers to the south of its previously known distribution.More recently, the species was repeteadly reported for Buenos Aires and La Plata cities (Chimento et al., 2011;Borsellino, 2012), and Vuelta de Obligado, San Pedro district (Chimento et al., 2011).The presence and nestling of the species on its southern geographical limit was considered by Chimento et al. (2011) as probably driven by climatic changes in the region.
The Green-backed Becard Pachyramphus viridis was observed for the first time in Buenos Aires province in 1989 (Narosky & Di Giacomo, 1993).Since then, the species expanded its distribution to several localities of the area (Krapovickas et al., 1992;Narosky & Di Giacomo, 1993;Grilli & Areta, 2002;Bodrati, 2001;Bodrati et al., 2006;Areta in Pagano & Mérida, 2009).Similarly, the Cardinal Paroaria capitata was not observed by ancient authors in the province (e.g., Holmberg, 1898;Burmeister, 1868;Pereyra, 1938).Klimaitis & Moschione (1987) stated the species was pres-ent though very scarce in Punta Lara.Narosky & Di Giacomo (1993) reported a large amount of localities at northern and eastern Buenos Aires province, and Pugnali and Chamorro (2008) and Zelaya & Pérez (2008) indicated that this species currently is common in Buenos Aires city.Also Chimento et al. (2012) reported new records for the Cardinal and said that it probably expanded its geographical range to the south of the province in recent times.Likewise, the Saltator Saltator similis was first found in the northern extreme of Buenos Aires province by Fernández (1991).Since then, it was found in other localities of the province, including Punta Lara and Atalaya (Bodrati et al., 2001b;Mérida & Bodrati, 2006;Bodrati & Sierra, 2009), and Buenos Aires city (Pugnali & Chamorro, 2008).
Previous to the 1980s, Phacellodomus ruber presence in Buenos Aires province was inferred from a single skin coming from Avellaneda district (Narosky &Di Giacomo, 1993).This species is related to wooded areas and forests from northern Argentina north to Santa Fe province (Olrog, 1963(Olrog, , 1979)).However, since 1989 the species has become more frequent in different localities at northeastern Buenos Aires province (Chebez & Haene, 1991;Narosky & Di Giacomo, 1993;Bodrati et al., 2001a).Bodrati et al. (2001a) considerably expanded the knowledge of the species in the province, and indicated that it is relatively frequent in Vuelta de Obligado (San Pedro district), where it nests.Similarly, in the early 20 th century Thamnophilus caerulescens had only two records in northeastern Buenos Aires province (Sclater, 1890;Holmberg, 1898), and was considered a rare species in the province by Narosky & Di Giacomo (1993).More recently, it was frequently reported in the studied area, with records from Zárate, San Isidro, Campana, San Pedro, Baradero and Llavallol districts, and Buenos Aires city (Narosky, 1983;Barbetti et al., 1985;Babarskas et al., 2003;Bodrati et al., 2001a;Pugnali & Chamorro, 2008;Lucero et al., 2011).Furthermore, in Baradero and Llavallol districts the species is relatively frequent (Bodrati et al., 2001a).
Several other species that were considered rare, scarce or hypothetical for Buenos Aires have been increasing its occurrence in the region.For example, up to late 1980s the Woodcreeper Lepidocolaptes angustirostris was considered a very rare species at Punta Lara Natural Reserve (Klimaitis & Moschione, 1987), whereas more recently it is considered "very common" and frequent in all environments (Pagano et al., 2012).The species is also very common in Buenos Aires city (F.L. Agnolin pers.obs.), and has expanded its southern and western distribution in several counties of the province (Haene, 2006;Chimento et al., 2012).The same may be said for Myiodynastes maculatus, which was a rare resident on the northern tip of the province, with only a few records (Narosky & Di Giacomo, 1993).Recent overviews indicate that the species is common at several localities, including La Plata city (F.L. Agnolin pers.obs.), Llavallol (Lucero et al., 2011), Avellaneda and Quilmes districts (Godoy et al., 2012), and Punta Lara Natural Reserve (Pagano et al., 2012).A similar pattern may be recognized for the Trushes Turdus rufiventris and T. amaurochalinus.The fomer was considered scarce by d' Orbigny (1847) and Withington (1888) in Buenos Aires neighborhood.However, since the 1960s the species has been increasing its abundance in the province (Narosky, 2012).Nowadays, this Thrush is probably one of the most frequent birds in several localities, including Buenos Aires city (Narosky, 2012;Narosky et al., 1996;Haene, 2006) and expanded its distribution towards the south in Buenos Aires province.Similarly, T. amaurochalinus was an uncommon species in the province, where it was frequent only in some streams of the Paraná Delta (Pereyra, 1938).Daguerre (1922) indicated it was a very rare species at Rosas (Las Flores district).It is today distributed along a large area in the province, including its southernmost limit, and it is very frequent along the coastal line, where this species increased its abundance at least since the 1990s (Narosky & Di Giacomo, 1993;Roesler, 2001;Maugeri, 2002;Haene, 2006).

Changes in mammals distribution
Three mammals species are known to have changed their distributional limits in the last decades (Table 6).
The occurrence in the last decades of some mid-to large mammals, including Dasypus novemcinctus, Cerdocyon thous, and Procyon cancrivorus, in the north of Buenos Aires province was interpreted by some authors as a result of more humid and temperate conditions in the area (Zamorano & Scillato-Yané, 2008;Fracassi et al., 2010).The latter species was reported by Fracassi et al., (2010) from several localities of the province, including the Reserva Natural Otamendi.This protected area was prospected in high detail during decades in search of mammals (Heinonen de Fortabat & Chebez, 1997;Pereira et al., 2003).Since these researches were unable to find P. cancrivorus, the arrival of the species in the area was probably recent (Fracassi et al., 2010).
In the same line, the new records of the micromammals Cryptonanus chacoensis, Deltamys kempi and Oligoryzomys nigripes in more southern localities than previously known (Udrizar Sauthier et al., 2005) may be due to an expansion in their range.Likewise, Holochilus chacarius was first recorded in Buenos Aires in 2004, where it was never found previously (Voglino et al., 2004;Courtalon et al., 2013).Nevertheless these four species were not considered in our study because the extension of their southern distributional limits could also be attributed to lack of historical collections.

DISCUSSION
This contribution indicates important changes on the geographical distribution of 115 species belonging to seven major groups of plants and animals.Plants, butterflies and birds were the groups with the larger number of southward expansions, with 44, 33, and 24 species respectively, whereas arachnids, mammals and turtles were represented by 8, 3 and 3 respectively.In addition, an increase in abundance was detected in a butterfly and some bird taxa.It is worth noting that several of these species have divergent ecological habits.The plants that have expanded their distribution encompass all known kinds of growth represented in riparian forests and marshes from northeastern Argentina and surrounding countries, with the single exception of parasitic plants (Table 7).This fact suggests there is no ecological bias in recently geographically-expanded species.The same may be said for birds, in which insectivorous, frugivorous and piscivorous species have been expanded southward (De La Peña, 2010).
Almost all taxa expanding their southern limits of distribution are inhabitants of South-American subtropical forests and surrounding wetlands, and show biogeographical affinities with Chaco and Paranaense biogeographical provinces.There are no reports of species from the Pampa or Patagonia biogeographical provinces that had increased their distributional area from south to north in the last decades.On the contrary, some Pampean taxa of Patagonian or Central Argentinean affinities disappeared from several localities and reduced their geographic distribution in the last centuries, mainly due to human disturbance, but also probably due to climatic change (Agnolin & Lucero, 2014;Teta et al., 2014;Agnolin & Rivero, 2014).In this regard, some taxa, like the rodent Ctenomys talarum and the birds Sturnella loyca and Geositta cunicularia, among others, moved towards more arid and cold regions (Agnolin & Lucero, 2014;Agnolin & Rivero, 2014).
With the aim to correlate these changes with the increase in some climatic values during the lasts centuries, it is necessary to rule out other factors that may produce distributional shifts in some species.A main change that occurred in the area of study during late 19 th and the 20 th centuries is the raise of intensive agriculture, which is clearly not a positive factor for native species (Rapoport, 1996).As stated by Hickling et al. (2006), the use of landscape negatively affects species lacking dispersal abilities to spread over these strongly modified and fragmented habitats.
Human introduction of several exotic tree species in the Pampa grasslands may enable some bird taxa increase their southern limits of geographic distributions (Chimento et al., 2012).Nevertheless, the area here studied had native woods, like the "talares" (Fig. 2), long before the first European explorations (Delucchi & Charra, 2012).
Probably, colonization of the La Plata River coast by the riparian subtropical rainforest is a climate-driven event (Schnack, 2000).In fact, it was hypothesized that it occurred when the Little Ice Age ended by the mid 19 th century (Deschamps et al., 2002;Deschamps & Tonni, 2007;Guerrero, 2014b).Whenever the time of appearance of riparian forest in the studied area, it is probable that this habitat richness steady increased since the end of 19 th century, as noticed early by William H. Hudson (Narosky & Gallegos, 1992) and Carlos L. Spegazzini (1905).Paraphrasing the last author, northeastern Buenos Aires province flora changed from xerophyte to hygrophyte between 1881 and 1905.Although more evidence is wanting, many species of plants and animals probably arrived from northern locations in that period (Guerrero, 2014b).Among the evidence listed in this paper, the tree Lonchocarpus nitidus could be a good example of those shifts.Most geographical changes listed in the present contribution may have taken place since 1970 to the date, when an important increase in temperature and rainfall has been registered in northern Buenos Aires province (Berbery et al., 2006;Servicio Meteorológico Nacional, 2015).Furthermore, Menéndez (2006) recognized a raise in the discharge of the La Plata Fluvial System over the last four decades.It is well-documented that in almost every raise in this fluvial system level, large masses of floating vegetation (locally called "camalotales") are dragged down and carry lot of individuals and propagules of diverse animal and plant species (Achaval et al., 1979;Guerrero et al., 2012;Katinas et al., 2013).This phenomenon has taken place at least since the colonial period (see e.g.Robertson, 1916), but in most cases, when tropical species arrived to Buenos Aires, they failed to colonize new environments and died due to severe winter temperatures (Spegazzini, 1905; see Hudson commentaries from Narosky & Gallegos, 1992).Otherwise, the local increase in temperature and humidity, and changes on hydrological parameters since the 1970s, may have enhanced and allowed the possibilities of raft dispersal and effective colonization for many taxa.

CONCLUSIONS
First, we summarized, analyzed, and discussed the distributional changes of plants and animals detected in recent times in northeastern part of Buenos Aires province, a well-known transitional area between forested galleries of the La Plata Fluvial System and Pampas grasslands.One hundred and fifteen species belonging to different major groups extended their geographical ranges towards southerly locations in northeastern Buenos Aires province by late 20 th and early 21 th centuries.Geographical extension was detected in species of each reviewed taxonomical group.The changes of geographical distribution limits observed in a large diversity of plant and animal taxa of ecologically divergent groups appear to be coeval with some wellknown climatic changes.Buenos Aires riparian forests as a whole show an incessant increment in species richness and a southward geographical expansion that probably represent ecological responses to climatic changes.Although we summarized distributional changes in well-sampled groups, it is highly probable that a greater part of the flora and fauna is being also affected by the same pattern.
This paper is the first comprehensive analysis demonstrating the possibility of an ecological response of a large number of animals and plants to recent climatic change in Argentina.It is clear that more studies are urgently needed, since most other aspects of the ecological and evolutionary responses to climate change remain largely unknown.Cabrera (1963Cabrera ( -1970) ) PLNR and Berisso district Moschione & Klimaitis (1988); Buet 233 (LP)

Name
Southern limit known in the 20 th century Source Present southern limit

Fig. 2 :
Fig. 2: Physical features of the study area and sites mentioned in the text.

Fig. 3 :
Fig. 3: Southernmost Erythrina crista-galli L. forests in Samborombón Bay.A-B: General view of the trees along the river coast (winter condition).C: Teucrium vesicarium Mill., a typical herb of the La Plata River hygrophilous forests.

Fig. 4 :
Fig. 4: Some sedimentary features of Punta Indio ridges (Parque Costero del Sur).Redrawn from Guerrero (2014a).A: General view of a stratigraphic cut in Erythrina crista-galli forests at Punta Indio.B: Detail of the same stratigraphic cut.Note the plastic buoy taken from the lower part of the strata.C: Recently formed ridge.Arrows indicate plastic waste embedded in the geoform.

Table 7 :
Plant species that expanded their distribution to northern Buenos Aires province and their growth habits.