\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[ngerman,greek,english]{babel}



\usepackage{float}








\begin{document}

\title{Temporal and spatial patterns of propagule deposition in the riparian
zones of mountain rivers}



\author[1]{Nihaib Flores-Galicia}%
\author[2]{Irma Trejo}%
\affil[1]{Posgrado en Ciencias Biológicas Universidad Nacional Autónoma de México Unidad de Posgrado Circuito de Posgrados Ciudad Universitaria Coyoacán 04510 Ciudad de México México}%
\affil[2]{Instituto de Geografía Universidad Nacional Autónoma de México Circuito de la Investigación Científica Ciudad Universitaria Coyoacán 04510 Ciudad de México México}%


\vspace{-1em}



  
  \date{May 27, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
Although the dispersal is important for riparian plants, few studies
have evaluated the patterns in species richness and composition of
propagules deposited by different dispersal types. In the present study
we evaluate the temporal and spatial patterns in the diversity of
propagules deposited by hydrochory and by other types of dispersal along
mountain rivers. To do this, we sampled the propagules deposited in the
riparian zone in a distance gradient with respect to the site of origin
of the rivers in two seasons. Regarding the temporal analyses, we found
no differences in the number of propagules between seasons. In the rainy
season we observed a greater number of species deposited by hydrochory,
while for other types of dispersal there was a greater number of species
in the dry season. Differences in composition were observed for
hydrochory but not for other types of dispersal. Regarding the spatial
analyses, there were no changes in the number of propagules deposited
along the river by hydrochory, while for other types of dispersal an
increase was observed in the dry season. A lower number of species
deposited by hydrochory along the river in the rainy season was
observed. Finally, we observed that turnover increases by other types of
dispersal in the dry season but not for hydrochory. The results
underline the importance of types of dispersal other than hydrochory in
the contribution of propagules dispersed and the temporal and spatial
particularities of the hydrochory in mountain rivers.%
\end{abstract}%



\sloppy


\textbf{1. Introduction}

Dispersal is the transport of individuals from their site of origin to
an establishment site (Cousens et al., 2008; Pijl, 1969). In plants this
transport is generally driven by one or several dispersal vectors, for
example, if the transport is by wind it's called anemochory, by an
animal it's called zoochory and if the transport is by water it's called
hydrochory (Boudell, 2016; Matthysen, 2012; Pijl, 1969). Given that for
plants the transport of propagules depends on dispersal vectors, the
dynamics of these vectors has important implications for plant
communities since dispersal has been observed to be important for the
patterns of species richness and composition of communities, the
coexistence of species and the maintenance of metacommunities (Boudell,
2016; Levine \& Murrell, 2003; Nilsson et al., 2010).

Hydrochory is an important source of propagules for riparian plant
communities, since it transports the greatest number of different
species' propagules to the riparian zones (Jansson et al., 2005; Leyer,
2006; Moggridge \& Gurnell, 2010; Neff \& Baldwin, 2005). For this
reason, great efforts have been made to understand this dispersal
mechanism in rivers (Hyslop \& Trowsdale, 2012; Nilsson et al., 2010).
These studies have shown that hydrochory has two important
characteristics that determine the spatial distribution of dispersed
propagules in the riparian zones along rivers: (i) the movement of
propagules is unidirectional and (ii) there is a downstream accumulation
of the propagules (Andersson et al., 2000; Nilsson et al., 2010). This
unidirectional movement and accumulation of species and propagules
transported downstream by the river is related to the increase in
species richness and the nesting of plant communities along rivers
(Kuglerov\selectlanguage{ngerman}á et al., 2015). This has served as a basis to explain the
diversity patterns of plant communities along rivers, synthesized in the
''River Collector Hypothesis'' (hereinafter referred to as RCH). The RCH
suggests that the species richness increases along the river to a
maximum point in the intermediate zones and then decreases towards the
mouth of the rivers, in addition, it supposes the nesting of the
upstream communities in the downstream ones (Nilsson et al., 2010).

In addition to these spatial changes, temporal variations in the
dispersal of propagules by hydrochory have been observed. The most
relevant pattern occurs in the season of greatest streamflow, which is
correlated with a greater number of propagules and species dispersed
along the rivers (Greet et al., 2011; Gurnell et al., 2008; Pettit \&
Froend, 2001). This increase in the number of dispersed propagules
depends on a greater streamflow, but it is also the result of the
synchronization of the reproductive phenology of the riparian species
with the maximum flow peaks of the water, producing a greater number of
propagules that can be dispersed (Pettit \& Froend, 2001).

The plants of the riparian communities, also have other vectors of
dispersal to move their propagules to other watersheds or riparian zones
through anemochory and zoochory (Fraaije et al., 2017). These types of
dispersal are important for the spatial distribution patterns of
propagules in riparian zones because for some species they are the first
dispersal vector that carries propagules from the parental plant to the
riparian zone along the river (Esper-Reyes et al., 2018; Fraaije et al.,
2017; Nilsson et al., 2010). These types of dispersal could be
particularly important for propagule movement in intermittent rivers in
which hydrochory propagule transport only occurs at certain times of the
year (Boland, 2017; Drezner et al., 2001; Schwab et al., 2018) or in
turbulent rivers where the disturbance of the floods limits the
establishment of the propagules deposited by hydrochory (Hasselquist et
al., 2015). However, there is little empirical studies on the patterns
of richness and composition of dispersal types other than hydrochory
along rivers and their temporal variations.

Another of the unknown aspects of dispersal in riparian zones is the
study of variations in the richness, composition and number of
propagules dispersed in rivers with specific geomorphological
characteristics, such as mountain rivers. The geomorphological and
hydrological characteristics of these rivers, such as the altitudinal
gradients, the steep slopes, the large confining sections and the
current velocity, increase their downstream transport capacity and
reduce their deposition of matter towards the riparian zones (Jacobsen,
2008; Meyer et al., 2007; Wohl, 2010) and thus, it is possible that the
deposition patterns of the propagules transported by hydrochory are
different from what has been observed in other sections of the rivers.

In this study, we contrast spatial and temporal changes in the number of
propagules, species, and species composition deposited by hydrochory and
other types of dispersal with increasing distance to the site of origin
of rivers in a mountainous system. For the temporal patterns we expect
that: (i) the abundance and species richness of propagules deposited by
hydrochory is greater in the rainy season than in the dry season, while
no changes are observed for other types of dispersal and (ii)
differences in composition between seasons for hydrochory but not for
other types of dispersal. Regarding spatial patterns, we expect that:
(iii) the number of species and propagules dispersed by hydrochory
increases with distance to the site of origin of rivers while remaining
constant for other types of dispersal, (iv) nesting pattern for
hydrochory but not for other dispersal types and (v) the turnover
remains constant for hydrochory-dispersed propagule communities and
increases for other dispersal types.

\textbf{2. Method}

2.1. Study area

The study area is limited to the upper area of \selectlanguage{english}\selectlanguage{english}the Papaloapan River in
the state of Oaxaca, southern Mexico. In this area the rivers drain from
a maximum altitude of 3,216 m a.s.l. towards a minimum altitude of 1,833
m a.s.l. Strahler order of rivers ranges from 1 at sites in the smallest
rivers (headwaters) to 5 at sites that are located on the largest rivers
(downstream). The flow ranges from 0.01 l/s to 2.5 l/s and has a
negative relationship with altitude (Flores-Galicia et al., 2021). The
climate in the upper part of the watershed corresponds to humid
temperate with summer rains and in the lower and middle part it
corresponds mainly to sub-humid temperate with summer rains. The upland
forests are \emph{Abies hickelii} and \emph{Pinus hartwegii} forests in
the upper areas and mixed forests of \emph{A. hickelli} -\emph{Pinus
patula} and \emph{Pinus pseudostrobus} var.\emph{apulcensis}
-\emph{Quercus crassifolia} towards the middle and low areas of the
watershed (Pina \& Trejo, 2014). The vegetation of the riparian zone
changes along the streams, in the headwaters arboreal elements of
species such as \emph{A} . \emph{hickelli} , \emph{Pinus}spp.,
\emph{Quercus} spp., towards the intermediate parts \emph{Alnus
acuminata} , \emph{Oreopanax xalapensis} and \emph{Meliosma dentata} ,
while in the lower areas \emph{A} . \emph{acuminata} and
\emph{Salixhumboldtiana} are observed (Flores-Galicia et al., 2021).

To evaluate the changes in the communities of propagules, nine sampling
sites were established in two tributary rivers (Yavesia's river and
Lachatao's river) that are part of the same drainage network in the
basin, the location of the sites was determined based on a progressive
criterion of distance with respect to the origin of the rivers (Fig. 1).

2.2. Sampling propagules

To characterize the communities of propagules dispersed by hydrochory
and other types of dispersal in the riparian zone, generative propagules
were collected, that is, those that are the product of the sexual
reproduction of plants such as seeds or fruits (Pijl, 1969) in two types
of traps that were placed in sediment deposition zones adjacent to the
streams: (i) Leyer boxes to collect propagules dispersed by hydrochory
and (ii) mesh traps to collect propagules dispersed by other types of
dispersal. Leyer boxes (\emph{sensu} Leyer, 2006) were boxes open at the
bottom, covered by a 0.15 mm mesh size at the top and fastened by wires.
The construction ensured the free flow of water, sediments, and
propagules into the box, inside an artificial turf mat were placed
(0.5x0.5 m) to retain the propagules. The boxes were tied to 75 cm long
metal rods to prevent them from being dragged by the waterflood (Araujo
et al., 2015). On the other hand, the mesh traps to collect propagules
dispersed by other types of dispersal consisted of extended squares (1.5
x 1.5 m) of shade cloth (1.5 mm mesh) that were placed near the Leyer
boxes. Leyer boxes were placed at the lowest line of perennial
vegetation (greenline) (Fig. 1c).

In each of the nine sampling sites, two Leyer boxes and three mesh traps
were placed to collect propagules dispersed by hydrochory and by other
types of dispersal (Fig. 1b). The traps were visited every two or three
months to collect the propagules trapped in them between January 2017
and January 2018 (they were visited five times: March, June, August, and
November 2017 and January 2018). At each visit the traps were removed
and new traps were placed, so that a total of 90 Leyer boxes and 135
mesh traps were placed throughout the sampling period. Due to river
flooding and other events, 36\% of the Leyer boxes (n=32) and 15\% of
the mesh traps (n=20) were lost. During this period, propagules in the
dry season (March 2017 and January 2018) and in the rainy season (June,
August, and November 2017) were collected.

The propagules were identified (to species level or otherwise assigned
to a morphospecies), counted and removed manually. The propagules were
compared with specimens deposited in the Collection of Fruits and Seeds
of the National Herbarium (MEXU), of the Institute of Biology of the
UNAM.

2.3. Data analysis

2.3.1. Temporal variations

To detect differences between seasons, a database was prepared
differentiating the propagules collected in the dry season (propagules
collected in March 2017 and January 2018) and the rainy season
(propagules collected in June, August and November 2017), with which
performed the following analyses in R ver. 4.0.3 (R Core Team, 2020).

Since differences in the number of propagules between seasons, a
standardization of the sampling effort was first carried out by randomly
selecting 52 traps for hydrochory (dry= 26 traps, rainy=26 traps) and 92
traps for other types of dispersal (dry= 46 traps, rainy= 46 traps).
Subsequently, and because the data were not normal, we performed a
Mann-Whitney test to determine differences in the number of propagules
between seasons.

To contrast species richness, a rarefaction analysis was performed using
the \emph{iNEXT} function (Hsieh et al., 2016) from the iNEXT package.
We calculated the estimated species richness
(\emph{q\textsuperscript{0}} ) and its 95\% confidence intervals for the
dry and rainy seasons considering the lower coverage that we recorded in
the traps (traps for hydrochory in the rainy season=0.995) (Hsieh et
al., 2016). Finally, to determine changes in species composition, a
permutational multivariate analysis of variance (PERMANOVA) was
performed, applying a Hellinger transformation to the abundance data
using the \emph{adonis} function from the vegan package in R (Oksanen et
al., 2013). For the PERMANOVA, a distance matrix was used that was
obtained with the Bray Curtis coefficient. To graphically evaluate the
associations in the composition of the propagules dispersed by
hydrochory and by other types of dispersal in the dry and rainy season,
an NMDS was performed with the \emph{metaMDS} function of the vegan
package (Oksanen et al., 2013).

2.3.2. Longitudinal variations along the streams

To evaluate changes in the abundance and richness of species with the
distance to the origin of the river, a Generalized Linear Mixed Effects
Model (GLMM) with a negative binomial link function was performed using
the \emph{glmer.nb} function of the lme4 package (Bates, 2010). The
number of propagules/m\textsuperscript{2} and the number of species
estimated at each site were used as a fixed effect and the stream in
which the sites were established (Yavesia river or Lachatao river) as a
random effect (Fig. 1).

To determine changes in the turnover and nesting of propagule
communities with increasing distance to the origin of the river, values
were obtained for the Simpson dissimilarity index
(\selectlanguage{greek}\emph{β\textsubscript{Sim}}\selectlanguage{english} ) and nesting between sites near the river
origin (site one: 0.5 km and site two: 0.8 km) and the downstream sites,
in this analysis the sites that were located in the Lachatao stream
(sites six, seven and nine) were excluded because they are located in a
different stream than the rest of the sites. The turnover and nesting
values were obtained using the functions \emph{vegdist}
and\emph{nestednodf} of vegan package (Oksanen et al., 2013).
Subsequently, a Pearson correlation analysis was carried out to
determine if there was a relationship between the distance to the origin
of the river and the turnover and nesting values.

\textbf{3. Results}

3.1. Temporal variations in the propagules

During the study period and considering the traps for hydrochory and for
other types of dispersal, a total of 43,025 propagules belonging to 106
species were collected. In the traps for hydrochory 5,435 propagules
belonging to 46 species were collected and in the traps for other types
of dispersal 37,590 propagules of 66 species were captured. No
differences were observed in the number of propagules collected between
the dry and rainy seasons in the hydrochory traps
(rainy:\(\overset{\overline{}}{x}\) = 152, S.D. = 410, dry:\(\overset{\overline{}}{\text{x\ }}\)=
57.38, S.D.= 102.83, Mann-Whitney\emph{U} = 441, \emph{p} = 0.06) or in
the traps for other types of dispersal (rainy \(\overset{\overline{}}{x}\) =
513.85, S.D.=990.92, dry: \(\overset{\overline{}}{x}\) = 173.39, S.D.= 324.77,
Mann-Whitney\emph{U} = 1157, \emph{p} = 0.44) (Fig. 2a). Regarding
species richness, a higher estimated species richness was observed in
the rainy season than in the dry season in the hydrochory traps (rainy:
\emph{q0} = 37.82, 95\% C.I.: 31.60-44.34; dry: \emph{q0} = 10.12, 95\%
C.I.: 7.93-12.31), while in the traps for other types of dispersal there
is a higher species richness estimated in the dry season than in the
rainy season (rainy: \emph{q0} = 17.79, 95\% C.I.: 16.88-18.72; dry:
\emph{q0}= 27.89, 95\% C.I.: 25.33-30.32) (Fig. 2b).

Regarding the composition, the PERMANOVA shows that in the hydrochory
traps the composition is different between the dry and rainy seasons
(pseudo-F= 2.55, \emph{p} = 0.02). Some of the species that were only
observed in the rainy season were conifers (\emph{Abies hickelli}
y\emph{Pinus} sp.), some composites (Asteraceae, Asteraceae 2 y
Asteraceae 6) and a grass species (Poaceae), in the dry
season\emph{Rumex} sp. was a characteristic species and species such
as\emph{Alnus acuminata} and \emph{Clematis dioica} were observed in
both seasons (Fig. 3, Appendix 1). With respect to the propagules
deposited by other types of dispersion, no differences were observed in
the composition between the seasons (pseudo-F= 0.75, \emph{p} = 0.62)
(Fig. 3).

3.2. Spatial changes of propagule communities along the river

Regarding the number of propagules, no changes were observed with the
increase in the distance to the origin of the river in the traps for
hydrochory, while for other types of dispersal an increase in the number
of propagules deposited in the dry season was observed (Fig. 4, table
1).

Regarding to the changes in species richness, a decrease in estimated
species richness was observed with increasing distance from the river
origin in hydrochory traps in the rainy season but not in the dry
season. While for other types of dispersal, no changes were observed in
the estimated species richness with the distance to the site of origin
of the river in any of the seasons (Fig. 5, table 2).

Finally, nesting values were low and turnover was high in traps for
hydrochory and for other types of dispersion in both seasons. No
relationships of nesting or turnover values with increasing distance to
sites near the river origin were observed in any of the seasons for
propagules deposited by hydrochory. For other types of dispersion, a
positive relationship was observed with the turnover of species in the
dry season (Fig. 6, table 3).

\textbf{4. Discussion}

The temporal variations in the species richness of propagules deposited
by hydrochory show similarities with what has been observed in other
rivers and what we propose in our hypotheses. These temporary changes
are determined by the increase in the level and volume of water in the
rivers during the rainy season (or higher water flow) which in turn
increase the number of species that are dispersed towards the riparian
zones (Boedtelje et al., 2004; Fraaije et al., 2017; Moggridge et al.,
2009). In contrast, the abundance of propagules dispersed by hydrochory
towards the riparian zone did not increase during the rainy season.
Previous work has found that there is a greater number of propagules
during the season of higher water flow in rivers due to the greater
capacity of propagule dispersal through water currents (Boedtelje et
al., 2004; Esper-Reyes et al., 2018; Fraaije et al., 2017; Moggridge \&
Gurnell, 2010; Naiman et al., 2010). However, there is no temporal trend
in the deposition of propagules by hydrochory and it has been suggested
that this may be due to the great production of propagules of one
species (e.g. \emph{Veronica anagallis-aquatica} ) throughout the year
(Gurnell et al., 2008), a similar phenomenon could be occurring in the
study area.

In our case, we observed that the dominant tree species in the riparian
zone (\emph{Alnus acuminata} ) (Flores-Galicia et al., 2021) had a peak
in propagule release that was detected in the traps for other types of
dispersal at the end of the rainy season (November 2017). Subsequently,
the increase was reflected in the hydrochory traps at the beginning of
the dry season (January 2018) (Annex 1). The effect of \emph{A.
acuminata} propagule production on temporal variations in the number of
propagules deposited by hydrochory is confirmed if this species is
eliminated from abundance analyses. By doing this, the number of
propagules deposited by hydrochory in the rainy season is greater than
in the dry season (rainy: \(\overset{\overline{}}{x}\) = 21.8, S.D. = 44.3, dry:
\(\overset{\overline{}}{\text{x\ }}\)= 3.1, S.D.= 6.3,\emph{W} = 502, \emph{d.f} .= 45,
\emph{p} \textless{}0.01). The foregoing indicates that, in this system,
the temporal patterns of abundance of propagules dispersed by hydrochory
are not only determined by the temporal variations in the flow of water
from the rivers, but also that the local production of propagules.

The differences in the composition of the propagules dispersed by
hydrochory between the dry and rainy seasons were consistent with our
hypothesis. These temporary changes in composition are related to
differences throughout the year in the production of propagules of the
species that make up the riparian communities or of the adjacent forests
(Esper-Reyes et al., 2018), the accumulation of these in the riparian
zones and their subsequent remobilization during river floods (Boedtelje
et al., 2004; Fraaije et al., 2017; Gurnell et al., 2008). In our system
we observed that some species with peaks of propagule production during
the rainy season were only observed during the same season in propagules
deposited by hydrochory, such as \emph{A. hickelli} , \emph{Pinus}
sp.,\emph{Solanum} sp and some Asteraceae (Asteraceae 2 y Asteraceae 6).

For the spatial dimension, there are contrasts between what our
hypotheses propose and what we observed in this study, specifically for
the richness patterns, the number of propagules and the composition of
the communities of propagules dispersed by hydrochory along the river.
Contrary to what was expected, a greater number of species dispersed by
hydrochory was not observed with increasing distance from the origin
site of the river. The absence of a positive relationship between the
number of species and the distance to the origin of the river may be the
result of the fact that downstream there was no accumulation of species
from upstream, as has been observed in other rivers (Andersson et al.,
2000; Andersson \& Nilsson, 2002). The nesting analysis supports the
above since the composition of the communities of the sites close to the
origin of the river (sites one and two) is not a subset of the
communities further away from the origin of the river. The low nesting
indicates that the species near the origin of the river were not
transported downstream (sites beyond 7 km) or if they did, the
propagules were not deposited in the downstream riparian zones and
continued their course in the column. of water beyond the study area.

Regarding the number of propagules deposited by hydrochory along the
rivers, our results contrast with what we propose in our hypotheses and
what has been observed in other studies (Andersson \& Nilsson, 2002;
Esper-Reyes et al., 2018). As occurs for the temporal variations in the
number of propagules, the absence of an increase in the propagules
deposited along the river could be related to the local production
of\emph{A. acuminata} . However, when \emph{A. acuminata} is eliminated
from the analyses, an increase in the number of propagules is observed
along the rivers in the hydrochory traps in the dry season (estimated=
0.15, \emph{z} = 2.65, \emph{p} = \textless{}0.01) but not in the rainy
season, where instead a decrease in the deposited propagules is observed
(estimated= -0.14, \emph{z} = -2.46, \emph{p} = 0.01). This same
analysis (exclusion of \emph{A.acuminata} ) in the traps for other types
of dispersal yields similar results (rainy: estimated= -0.20, \emph{z} =
-3.04, \emph{p} = \textless{}0.01; dry: estimated= 0.17, \emph{z} =
2.42, \emph{p} = 0.01). This could indicate that the production of
propagules in the sites near the origin of the river is greater in the
rainy season, which increases the deposition of propagules by hydrochory
in the area, while in the dry season there is a greater production of
propagules in the sites furthest from the origin of the river.

The results that we observed with respect to the spatial dimension
(absence of relationship between the distance to the origin of the river
with the estimated species richness or with the number of propagules,
absence of nesting of the upstream communities in those of downstream),
has important implications for theoretical frameworks such as RHC that
hypothesize regarding longitudinal changes in diversity of riparian
plant communities. The RHC postulate that the number of plant species
increases to a maximum point in the intermediate zone of the rivers from
which it decreases towards its mouth, these changes are associated with:
(i) a linear increase in the disturbance in the riparian zones at along
the river and (ii) a constant increase in the number of species and
propagules dispersed by hydrochory (Nilsson et al., 1994, 2010). As
there is no greater deposition of species and propagules deposited
downstream, the patterns of diversity of the riparian plant communities
that the RHC supposes could not be observed in rivers of mountainous
systems (see for example Flores-Galicia et al., 2021; Pielech, 2021).

Some methodological limitations of this work did not allow us to
conclude whether the contrasts between what we propose in our hypotheses
with respect to the spatial distribution patterns of the propagules
along the river (that is, a greater number of propagules and species
deposited by hydrochory along the river, as well as nesting of the
upstream communities in the downstream communities) and what we observed
(absence of changes in the number of propagules, in the richness and
decrease in the nesting of the communities). This is due to the fact
that in this system: (i) the propagules transported in the water column
travel a shorter distance than has been observed in other studies
(Andersson et al., 2000; Boedeltje et al., 2003) or (ii) the propagules
are effectively transported over long distances but due to the
characteristic erosive capacity of mountain rivers (Wohl, 2010) the
propagules deposited in the riparian zone are quickly remobilized to
downstream and were not detected in our traps. Future studies could
determine which of these hypotheses is correct through controlled
propagule release experiments and the measurement of the distances they
travel (Boland, 2017; da Cunha et al., 2017) or through sampling of
propagules in the water column (Boedeltje et al., 2003).

\textbf{Conclusion}

Hydrochory in tropical mountain systems has characteristic deposition
patterns that do not agree with what has been observed in rivers with
different geomorphological characteristics or in complete rivers
(origin-mouth). In tropical mountain rivers, the contribution of
propagules by other types of dispersal and the spatial and temporal
changes in the local production of propagules by the riparian plant
species have a decisive influence on the spatial and temporal patterns
of deposition of the dispersed propagules by hydrochory. The dynamics of
the transport of propagules in the water column remains unknown, so it
is necessary to increase efforts to understand in depth the process of
dispersion in mountain rivers.

\textbf{References}

Andersson, E., \& Nilsson, C. (2002). Temporal variation in the drift of
plant litter and propagules in a small boreal river. \emph{Freshwater
Biology} , \emph{47} (9), 1674--1684.
https://doi.org/https://doi.org/10.1046/j.1365-2427.2002.00925.x

Andersson, E., Nilsson, C., \& Johansson, M. E. (2000). Plant dispersal
in boreal rivers and its relation to the diversity of riparian
flora.\emph{Journal of Biogeography} , \emph{27} (5), 1095--1106.
https://doi.org/10.1046/j.1365-2699.2000.00481.x

Bates, D. M. (2010). \emph{lme4: Mixed-effects modeling with R} .
Springer New York.

Boedeltje, G., Bakker, J. P., Bekker, R. M., Van Groenendael, J. M., \&
Soesbergen, M. (2003). Plant dispersal in a lowland stream in relation
to occurrence and three specific life-history traits of the species in
the species pool. \emph{Journal of Ecology} , \emph{91} (5), 855--866.
https://doi.org/https://doi.org/10.1046/j.1365-2745.2003.00820.x

Boedtelje, G., Bakker, J., Ten, A., Van Groenendael, J. M., \&
Soesbergen, M. (2004). Dispersal phenology of hydrochorous plants in
relation to discharge, seed release time and buoyancy of seeds: the
flood pulse concept supported. \emph{Journal of Ecology} , \emph{92}
(5), 786--796. https://doi.org/10.1111/j.0022-0477.2004.00906.x

Boland, J. M. (2017). Linking seedling spatial patterns to seed
dispersal processes in an intermittent stream. \selectlanguage{ngerman}\emph{Madroño} ,\emph{64}
(2), 10, 61--70. https://doi.org/10.3120/0024-9637-64.2.61

Boudell, J. A. (2016). Metacommunity Dynamics of Riparian Ecosystems. In
C. M. Finlayson, M. Everard, K. Irvine, R. J. McInnes, B. A. Middleton,
A. A. van Dam, \& N. C. Davidson (Eds.), \emph{The Wetland Book: I:
Structure and Function, Management and Methods} (pp. 1--8). Springer
Netherlands. https://doi.org/10.1007/978-94-007-6172-8\_48-5

Cousens, R., Dytham, C., \& Law, R. (2008). \selectlanguage{english}\emph{Dispersal in Plants :
A Population Perspective} (O. U. Press (ed.)).
https://doi.org/10.1093/acprof:oso/9780199299126.001.0001

da Cunha, A. C., Mustin, K., dos Santos, E. S., dos Santos, E. W. G.,
Guedes, M. C., Cunha, H. F. A., Rosman, P. C. C., \& Sternberg, L. da S.
L. (2017). Hydrodynamics and seed dispersal in the lower
Amazon.\emph{Freshwater Biology} , \emph{62} (10), 1721--1729.
https://doi.org/https://doi.org/10.1111/fwb.12982

Drezner, T. D., Fall, P. L., \& Stromberg, J. C. (2001). Plant
distribution and dispersal mechanisms at the Hassayampa River Preserve,
Arizona, USA. \emph{Global Ecology and Biogeography} , \emph{10} (2),
205--217.
https://doi.org/https://doi.org/10.1046/j.1466-822x.2001.00216.x

Esper-Reyes, K. A., Mariano, N. A., Alcala, R. E., Bonilla-Barbosa, J.
R., Flores-Franco, G., \& Wehncke, E. V. (2018). Seed dispersal by
rivers in tropical dry forests: An overlooked process in tropical
central Mexico. \emph{Journal of Vegetation Science} , \emph{29} (1),
62--73. https://doi.org/https://doi.org/10.1111/jvs.12595

Flores-Galicia, N., Trejo, I., \& Ramirez-Marcial, N. (2021).
Environment-driven changes in diversity of riparian plant communities
along a mountain river. \emph{Ecology and Evolution} , \emph{11} (10),
5690--5701. https://doi.org/https://doi.org/10.1002/ece3.7472

Fraaije, R. G. A., Moinier, S., van Gogh, I., Timmers, R., van Deelen,
J. J., Verhoeven, J. T. A., \& Soons, M. B. (2017). Spatial patterns of
water-dispersed seed deposition along stream riparian
gradients.\emph{PLOS ONE} , \emph{12} (9), e0185247-.
https://doi.org/10.1371/journal.pone.0185247

Greet, J., Aangus Webb, J., \& Cousens, R. D. (2011). The importance of
seasonal flow timing for riparian vegetation dynamics: a systematic
review using causal criteria analysis. \emph{Freshwater Biology}
,\emph{56} (7), 1231--1247.
https://doi.org/https://doi.org/10.1111/j.1365-2427.2011.02564.x

Gurnell, A., Thompson, K., Goodson, J., \& Moggridge, H. (2008).
Propagule deposition along river margins: linking hydrology and
ecology.\emph{Journal of Ecology} , \emph{96} (3), 553--565.
https://doi.org/https://doi.org/10.1111/j.1365-2745.2008.01358.x

Hasselquist, E. M., Nilsson, C., Hjalten, J., Jorgensen, D., Lind, L.,
\& Polvi, L. E. (2015). Time for recovery of riparian plants in restored
northern Swedish streams: a chronosequence study. \emph{Ecological
Applications} , \emph{25} (5), 1373--1389.
https://doi.org/https://doi.org/10.1890/14-1102.1

Hsieh, T. C., Ma, K. H., \& Chao, A. (2016). iNEXT: an R package for
rarefaction and extrapolation of species diversity (Hill
numbers).\emph{Methods in Ecology and Evolution} , \emph{7} (12),
1451--1456. https://doi.org/https://doi.org/10.1111/2041-210X.12613

Hyslop, J., \& Trowsdale, S. (2012). A review of hydrochory (seed
dispersal by water) with implications for riparian
rehabilitation.\emph{Journal of Hydrology (New Zealand)} , \emph{51}
(2), 137--152. www.jstor.org/stable/43945038

Jacobsen, D. (2008). Tropical High-Altitude Streams. In D. B. T.-T. S.
E. Dudgeon (Ed.), \emph{Aquatic Ecology} (pp. 219--VIII). Academic
Press. https://doi.org/https://doi.org/10.1016/B978-012088449-0.50010-8

Jansson, R., Zinko, U., Merritt, D. M., \& Nilsson, C. (2005).
Hydrochory increases riparian plant species richness: a comparison
between a free-flowing and a regulated river. \emph{Journal of Ecology}
,\emph{93} (6), 1094--1103.
https://doi.org/https://doi.org/10.1111/j.1365-2745.2005.01057.x

Kuglerova, L., Jansson, R., Sponseller, R. A., Laudon, H., \&
Malm-Renofalt, B. (2015). Local and regional processes determine plant
species richness in a river-network metacommunity. \emph{Ecology}
,\emph{96} (2), 381--391.
https://doi.org/https://doi.org/10.1890/14-0552.1

Levine, J. M., \& Murrell, D. J. (2003). The community-level
consequences of seed dispersal patterns. \emph{Annual Review of Ecology,
Evolution, and Systematics} , \emph{34} (1), 549--574.
https://doi.org/10.1146/annurev.ecolsys.34.011802.132400

Leyer, I. (2006). Dispersal, diversity and distribution patterns in
pioneer vegetation: The role of river-floodplain
connectivity.\emph{Journal of Vegetation Science} , \emph{17} (4),
407--416.
https://doi.org/10.1658/1100-9233(2006)17{[}407:DDADPI{]}2.0.CO;2

Matthysen, E. (2012). Multicausality of dispersal: a review. In J.
Clobert, M. Baguette, T. G. Benton, \& J. M. Bullock
(Eds.),\emph{Dispersal ecology and evolution} . Oxford University Press
Oxford, UK.

Meyer, J. L., Strayer, D. L., Wallace, J. B., Eggert, S. L., Helfman, G.
S., \& Leonard, N. E. (2007). The contribution of headwater streams to
biodiversity in river networks. \emph{Journal of the American Water
Resources Association} , \emph{43} (1), 86--103.
https://doi.org/https://doi.org/10.1111/j.1752-1688.2007.00008.x

Moggridge, H. L., \& Gurnell, A. M. (2010). Hydrological controls on the
transport and deposition of plant propagules within riparian
zones.\emph{River Research and Applications} , \emph{26} (4), 512--527.
https://doi.org/https://doi.org/10.1002/rra.1273

Moggridge, H. L., Gurnell, A. M., \& Mountford, J. O. (2009). Propagule
input, transport and deposition in riparian environments: the importance
of connectivity for diversity. \emph{Journal of Vegetation Science}
,\emph{20} (3), 465--474.
https://doi.org/https://doi.org/10.1111/j.1654-1103.2009.05498.x

Naiman, R. J., Decamps, H., \& McClain, M. E. (2010). \emph{Riparia:
ecology, conservation, and management of streamside communities} .
Elsevier.

Neff, K. P., \& Baldwin, A. H. (2005). Seed dispersal into wetlands:
Techniques and results for a restored tidal freshwater
marsh.\emph{Wetlands} , \emph{25} (2), 392--404.
https://doi.org/10.1672/14

Nilsson, C., Brown, R. L., Jansson, R., \& Merritt, D. M. (2010). The
role of hydrochory in structuring riparian and wetland
vegetation.\emph{Biological Reviews} , \emph{85} (4), 837--858.
https://doi.org/https://doi.org/10.1111/j.1469-185X.2010.00129.x

Nilsson, C., Ekblad, A., Dynesius, M., Backe, S., Gardfjell, M.,
Carlberg, B., Hellqviist, S., \& Jansson, R. (1994). A Comparison of
Species Richness and Traits of Riparian Plants between a Main River
Channel and Its Tributaries. \emph{Journal of Ecology} , \emph{82} (2),
281--295. https://doi.org/10.2307/2261296

Oksanen, J., Simspson, G. L., Blanchet, F. G., Kindt, R., Legendre, P.,
Minchin, P. R., O'Hara, R., Solymos, P., Stevens, M. H. H., Szoecs, E.,
Wagner, H., Barbour, M., Bedward, M., Bolker, B., Borcard, D., Carvalho,
G., Chirico, M., Caceres, M. De, Durand, S., \ldots{} Weedon, J.
(2013).\emph{Package `Vegan'. Community Ecology Package} .
https://cran.r-project.org/package=vegan

Pettit, N. E., \& Froend, R. H. (2001). Availability of seed for
recruitment of riparian vegetation: a comparison of a tropical and a
temperate river ecosystem in Australia. \emph{Australian Journal of
Botany} , \emph{49} (4), 515--528. https://doi.org/10.1071/BT00059

Pielech, R. (2021). Plant species richness in riparian forests:
comparison to other forest ecosystems, longitudinal patterns, role of
rare species and topographic factors. \emph{Forest Ecology and
Management} , \emph{496} , 119400.
https://doi.org/https://doi.org/10.1016/j.foreco.2021.119400

Pijl, L. Van der. (1969). \emph{Principles of dispersal in higher
plants} . Springer. https://doi.org/978-3-662-00799-0

Pina, E., \& Trejo, I. (2014). Densidad poblacional y caracterizacion de
habitat del venado cola blanca en un bosque templado de Oaxaca,
Mexico.\emph{Acta Zoologica Mexicana} , \emph{30} , 114--134.

R Core Team. (2020). \emph{R: A language and environment for statistical
computing} . Vienna, Austria.

Schwab, A., Stammel, B., \& Kiehl, K. (2018). Seed dispersal via a new
watercourse in a reconnected floodplain: differences in species groups
and seasonality. \emph{Restoration Ecology} , \emph{26} (S2),
S103--S113. https://doi.org/https://doi.org/10.1111/rec.12677

Wohl, E. (2010). Mountain Drainage Basins. In E. Wohl
(Ed.),\emph{Mountain Rivers Revisited} (pp. 13--102). American
Geophysical Union.
https://doi.org/https://doi.org/10.1002/9781118665572.ch2

\textbf{Data availability}

Propagule sampling data will be accessible via Figshare data repository.

\textbf{Tables}

\textbf{Table 1. Generalized mixed effects linear models to the
association between the distance to the origin site of the river and the
number of propagules collected in the traps for hydrochory and other
types of dispersal.} (*) Denotes significant effects. Var. = variance of
the random effect (river), S.D. = standard deviation, Est. = estimate of
the fixed effect (distance to the origin of the river), S.E. = standard
error.\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
\textbf{Type of trap} & \textbf{Season} & \textbf{Random effect} &
\textbf{Random effect} & \textbf{Fixed effect} & \textbf{Fixed effect} &
\textbf{Fixed effect} & \textbf{Fixed effect}\tabularnewline
\midrule
\endhead
& & \textbf{Var.} & \textbf{S. D.} & \textbf{Est.} & \textbf{S. E.} & z
& p\tabularnewline
\textbf{Hydrochory} & Rainy & \textless{}0.01 & \textless{}0.01 & 0.01 &
0.11 & 0.12 & 0.9\tabularnewline
& Dry & \textless{}0.01 & \textless{}0.01 & 0.27 & 0.14 & 1.87 &
0.06\tabularnewline
\textbf{Other type of dispersion} & Rainy & \textless{}0.01 &
\textless{}0.01 & 0.07 & 0.06 & 1.10 & 0.27\tabularnewline
& Dry & \textless{}0.01 & \textless{}0.01 & 0.16 & 0.07 & 2.42 &
0.01*\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 2. Linear generalized mixed effects models to the
association between the distance to the origin site of the river and the
richness of species in the traps for hydrochory and other types of
dispersal.} (*) Denotes significant effects. Var. = variance of the
random effect (river), S.D. = standard deviation, Est. = estimate of the
fixed effect (distance to the origin of the river), S.E. = standard
error.\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
\textbf{Type of trap} & \textbf{Season} & \textbf{Random effect} &
\textbf{Random effect} & \textbf{Fixed effect} & \textbf{Fixed effect} &
\textbf{Fixed effect} & \textbf{Fixed effect}\tabularnewline
\midrule
\endhead
& & \textbf{Var.} & \textbf{S. D.} & \textbf{Est.} & \textbf{S. E.} & z
& p\tabularnewline
\textbf{Hydrochory} & Rainy & \textless{}0.01 & \textless{}0.01 & 0.01 &
-0.04 & -1.96 & 0.05*\tabularnewline
& Dry & \textless{}0.01 & 0.01 & 0.09 & \textless{}-0.01 & -0.13 &
0.89\tabularnewline
\textbf{Other type of dispersion} & Rainy & \textless{}0.01 &
\textless{}0.01 & 0.01 & \textless{}0.01 & 0.03 & 0.97\tabularnewline
& Dry & \textless{}0.01 & 0.03 & 0.05 & \textless{}0.01 & 0.14 &
0.87\tabularnewline
\bottomrule
\end{longtable}

\selectlanguage{greek}\textbf{Table 3. Relationship between the increase in the distance to
the sites closest to the origin of the river, the turnover
(\emph{β\textsubscript{Sim}}) and nesting (NODF) (\emph{β} diversity)}\selectlanguage{english} .
(*) Denotes significant relationships. \emph{r\textsubscript{P}} =
Pearson correlation.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\textbf{Type of trap} & \textbf{Season} & \selectlanguage{greek}\textbf{Measure of \emph{β}
diversity}\selectlanguage{english} & r\textsubscript{P} & p\tabularnewline
\midrule
\endhead
\textbf{Hydrochory} & Rainy & Nestedness & -0.62 & 0.14\tabularnewline
& & Turnover & 0.64 & 0.12\tabularnewline
& Dry & Nestedness & -0.74 & 0.57\tabularnewline
& & Turnover & 0.74 & 0.57\tabularnewline
\textbf{Other type of dispersion} & Rainy & Nestedness & -0.65 &
0.11\tabularnewline
& & Turnover & 0.56 & 0.19\tabularnewline
& Dry & Nestedness & -0.69 & 0.06\tabularnewline
& & Turnover & 0.79 & 0.03*\tabularnewline
\bottomrule
\end{longtable}

\textbf{Figures}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1. Location of the sampling sites in two rivers of the
upper area of the Papaloapan River.} (a) Nine sampling sites were
established based on a progressive criterion of distance from the origin
of the river. (b and c) At each site, traps were established to collect
propagules dispersed by hydrochory (Leyer boxes) and for propagules
dispersed by other types of dispersal (mesh traps).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2. Mean number of propagules and species richness of
propagules in the traps for hydrochory and the traps for other types of
dispersal} . (a) No differences were observed between the rainy and dry
seasons in the number of propagules for any of the traps. (b) For
species richness, it was higher in the wet season than in the dry season
in hydrochory traps, while for other types of dispersal it was higher in
the dry season than in the rainy season. Shading indicates the rainy
season.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3. Ordination of seed traps collections during two
seasons (rainy: June-2017, August-2017 and November-2017; dry:
March-2017 and January-2018) in the hydrochory traps (a) and for other
types of dispersion (b).} Species with \textgreater{} 10 registered
individuals are shown with a black dot (the names of the species are
found in Appendix 1).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4. Changes in the number of propagules
(propagules/m\textsuperscript{2}) with increasing distance to the origin
site of the river in the dry and rainy seasons.} (A) propagules
collected in traps for hydrochory, (B) propagules collected in traps for
other types of dispersal.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 5. Changes in species richness with increasing distance
to the origin site of the river in the dry and rainy seasons.} (A)
species richness in traps for hydrochory, (B) species richness in traps
for other types of dispersal. Trend lines are shown for those
significant relationships (\emph{p} \textless{}0.05).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 6. Changes in the turnover and nesting of the communities
with the increase in the distance to the sites near the origin of the
river.} (a) Traps for hydrochory in the dry season, (b) traps for
hydrochory in the rainy season, (c) traps for other types of dispersion
in the dry season, (d) traps for other types of dispersion in the rainy
season. Filled bullets correspond to nesting values, unfilled bullets
correspond to replacement values. Trend lines are shown for significant
relationships.

\textbf{Appendices}

Appendix 1. Abundance of propagules (log of number of
propagules/m\textsuperscript{2}) by species collected in traps for
hydrochory and in traps for other types of dispersal. Species that had
more than 10 individuals are show. In parentheses, the code name of the
species. The gray shade indicates the collections corresponding to the
rainy season (July, August, and November 2017).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

