TY  - GEN
A1  - Bergholz, Kolja
A1  - Sittel, Lara-Pauline
A1  - Ristow, Michael
A1  - Jeltsch, Florian
A1  - Weiß, Lina
T1  - Pollinator guilds respond contrastingly at different scales to landscape parameters of land-use intensity
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Land-use intensification is the main factor for the catastrophic decline of insect pollinators. However, land-use intensification includes multiple processes that act across various scales and should affect pollinator guilds differently depending on their ecology. We aimed to reveal how two main pollinator guilds, wild bees and hoverflies, respond to different land-use intensification measures, that is, arable field cover (AFC), landscape heterogeneity (LH), and functional flower composition of local plant communities as a measure of habitat quality. We sampled wild bees and hoverflies on 22 dry grassland sites within a highly intensified landscape (NE Germany) within three campaigns using pan traps. We estimated AFC and LH on consecutive radii (60–3000 m) around the dry grassland sites and estimated the local functional flower composition. Wild bee species richness and abundance was positively affected by LH and negatively by AFC at small scales (140–400 m). In contrast, hoverflies were positively affected by AFC and negatively by LH at larger scales (500–3000 m), where both landscape parameters were negatively correlated to each other. At small spatial scales, though, LH had a positive effect on hoverfly abundance. Functional flower diversity had no positive effect on pollinators, but conspicuous flowers seem to attract abundance of hoverflies. In conclusion, landscape parameters contrarily affect two pollinator guilds at different scales. The correlation of landscape parameters may influence the observed relationships between landscape parameters and pollinators. Hence, effects of land-use intensification seem to be highly landscape-specific.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1298 
KW  - hoverflies
KW  - landscape homogenization
KW  - plant functional trait
KW  - syrphids
KW  - wild bees
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-577307
SN  - 1866-8372
IS  - 1298
ER  - 
TY  - GEN
A1  - Bergholz, Kolja
A1  - Kober, Klarissa
A1  - Jeltsch, Florian
A1  - Schmidt, Kristina
A1  - Weiß, Lina
T1  - Trait means or variance
BT  - What determines plant species' local and regional occurrence in fragmented dry grasslands?
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - One of the few laws in ecology is that communities consist of few common and many rare taxa. Functional traits may help to identify the underlying mechanisms of this community pattern, since they correlate with different niche dimensions. However, comprehensive studies are missing that investigate the effects of species mean traits (niche position) and intraspecific trait variability (ITV, niche width) on species abundance. In this study, we investigated fragmented dry grasslands to reveal trait-occurrence relationships in plants at local and regional scales. We predicted that (a) at the local scale, species occurrence is highest for species with intermediate traits, (b) at the regional scale, habitat specialists have a lower species occurrence than generalists, and thus, traits associated with stress-tolerance have a negative effect on species occurrence, and (c) ITV increases species occurrence irrespective of the scale. We measured three plant functional traits (SLA = specific leaf area, LDMC = leaf dry matter content, plant height) at 21 local dry grassland communities (10 m × 10 m) and analyzed the effect of these traits and their variation on species occurrence. At the local scale, mean LDMC had a positive effect on species occurrence, indicating that stress-tolerant species are the most abundant rather than species with intermediate traits (hypothesis 1). We found limited support for lower specialist occurrence at the regional scale (hypothesis 2). Further, ITV of LDMC and plant height had a positive effect on local occurrence supporting hypothesis 3. In contrast, at the regional scale, plants with a higher ITV of plant height were less frequent. We found no evidence that the consideration of phylogenetic relationships in our analyses influenced our findings. In conclusion, both species mean traits (in particular LDMC) and ITV were differently related to species occurrence with respect to spatial scale. Therefore, our study underlines the strong scale-dependency of trait-abundance relationships.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1151 
KW  - LMA
KW  - niche width
KW  - plant functional trait
KW  - scale-dependency
KW  - species abundance
KW  - trait-environment relationship
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-519905
SN  - 1866-8372
SP  - 3357
EP  - 3365
ER  - 
TY  - THES
A1  - Bergholz, Kolja
T1  - Trait-based understanding of plant species distributions along environmental gradients
T1  - Zum Verständnis der Verbreitung von Pflanzen entlang von umweltgradienten auf der Basis von funktionellen Eigenschaften
N2  - For more than two centuries, plant ecologists have aimed to understand how environmental gradients and biotic interactions shape the distribution and co-occurrence of plant species. In recent years, functional trait–based approaches have been increasingly used to predict patterns of species co-occurrence and species distributions along environmental gradients (trait–environment relationships). Functional traits are measurable properties at the individual level that correlate well with important processes. Thus, they allow us to identify general patterns by synthesizing studies across specific taxonomic compositions, thereby fostering our understanding of the underlying processes of species assembly. However, the importance of specific processes have been shown to be highly dependent on the spatial scale under consideration. In particular, it remains uncertain which mechanisms drive species assembly and allow for plant species coexistence at smaller, more local spatial scales. Furthermore, there is still no consensus on how particular environmental gradients affect the trait composition of plant communities. For example, increasing drought because of climate change is predicted to be a main threat to plant diversity, although it remains unclear which traits of species respond to increasing aridity. Similarly, there is conflicting evidence of how soil fertilization affects the traits related to establishment ability (e.g., seed mass). In this cumulative dissertation, I present three empirical trait-based studies that investigate specific research questions in order to improve our understanding of species distributions along environmental gradients. 
In the first case study, I analyze how annual species assemble at the local scale and how environmental heterogeneity affects different facets of biodiversity—i.e. taxonomic, functional, and phylogenetic diversity—at different spatial scales. The study was conducted in a semi-arid environment at the transition zone between desert and Mediterranean ecosystems that features a sharp precipitation gradient (Israel). Different null model analyses revealed strong support for environmentally driven species assembly at the local scale, since species with similar traits tended to co-occur and shared high abundances within microsites (trait convergence). A phylogenetic approach, which assumes that closely related species are functionally more similar to each other than distantly related ones, partly supported these results. However, I observed that species abundances within microsites were, surprisingly, more evenly distributed across the phylogenetic tree than expected (phylogenetic overdispersion). Furthermore, I showed that environmental heterogeneity has a positive effect on diversity, which was higher on functional than on taxonomic diversity and increased with spatial scale. The results of this case study indicate that environmental heterogeneity may act as a stabilizing factor to maintain species diversity at local scales, since it influenced species distribution according to their traits and positively influenced diversity. All results were constant along the precipitation gradient.
In the second case study (same study system as case study one), I explore the trait responses of two Mediterranean annuals (Geropogon hybridus and Crupina crupinastrum) along a precipitation gradient that is comparable to the maximum changes in precipitation predicted to occur by the end of this century (i.e., −30%). The heterocarpic G. hybridus showed strong trends in seed traits, suggesting that dispersal ability increased with aridity. By contrast, the homocarpic C. crupinastrum showed only a decrease in plant height as aridity increased, while leaf traits of both species showed no consistent pattern along the precipitation gradient. Furthermore, variance decomposition of traits revealed that most of the trait variation observed in the study system was actually found within populations. I conclude that trait responses towards aridity are highly species-specific and that the amount of precipitation is not the most striking environmental factor at this particular scale.
In the third case study, I assess how soil fertilization mediates—directly by increased nutrient addition and indirectly by increased competition—the effect of seed mass on establishment ability. For this experiment, I used 22 species differing in seed mass from dry grasslands in northeastern Germany and analyzed the interacting effects of seed mass with nutrient availability and competition on four key components of seedling establishment: seedling emergence, time of seedling emergence, seedling survival, and seedling growth. (Time of) seedling emergence was not affected by seed mass. However, I observed that the positive effect of seed mass on seedling survival is lowered under conditions of high nutrient availability, whereas the positive effect of seed mass on seedling growth was only reduced by competition. Based on these findings, I developed a conceptual model of how seed mass should change along a soil fertility gradient in order to reconcile conflicting findings from the literature. In this model, seed mass shows a U-shaped pattern along the soil fertility gradient as a result of changing nutrient availability and competition. 
Overall, the three case studies highlight the role of environmental factors on species distribution and co-occurrence. Moreover, the findings of this thesis indicate that spatial heterogeneity at local scales may act as a stabilizing factor that allows species with different traits to coexist. In the concluding discussion, I critically debate intraspecific trait variability in plant community ecology, the use of phylogenetic relationships and easily measured key functional traits as a proxy for species’ niches. Finally, I offer my outlook for the future of functional plant community research.
N2  - Seit über 200 Jahre erforschen Ökologen den Einfluss von Umweltgradienten, biotischen Interaktionen und neutralen Prozessen auf die Artenzusammensetzung von Pflanzengemeinschaften. Um generelle Muster und die zugrundeliegenden Mechanismen unabhängig von der gegeben Artenzusammensetzung besser zu verstehen, wurden in den letzten Jahren vermehrt funktionellen Eigenschaften (‚functional traits‘) als methodischen Ansatz genutzt. Es wurde deutlich, dass die bestimmenden Prozesse abhängig von der betrachteten räumlichen Skala sind. Vor allem ist unklar, in wieweit Umweltheterogenität auf kleiner, lokaler Skala die Artenzusammensetzung beeinflusst. Des Weiteren ist Skalenabhängigkeit wichtig um den Einfluss von spezifischen Umweltgradienten, wie Trockenheit oder Bodenfertilität,  auf die funktionelle Eigenschaften von Pflanzengemeinschaften zu ermitteln. 
In der vorliegenden Dissertation untersuche ich in drei unabhängigen, empirischen Studien den Einfluss von Umweltgradienten bzw. Umweltheterogenität auf die funktionellen Eigenschaften von Pflanzengemeinschaften unter besonderer Berücksichtigung der Skalenabhängigkeit. In der ersten Fallstudie prüfe ich welche Faktoren die Artenzusammensetzung in einem semi-ariden Ökosystem (Israel), das von einjährigen Pflanzen dominiert wird, auf lokaler Skala bestimmen. Ich kann zeigen, dass vor allem Arten mit ähnlichen funktionellen Eigenschaften in Mikrohabitaten auftreten, das auf eine Selektion durch Umweltfaktoren hindeutet. Des Weiteren kann ich zeigen, dass mit Zunahme der Umweltheterogenität des Habitats die Diversität der funktionellen Eigenschaften sowie die Artendiversität in den Pflanzengemeinschaften zunehmen. Aus diesen Ergebnissen folgere ich, dass lokale Umweltheterogenität ein wichtiger Faktor für die Koexistenz der Pflanzenarten ist. Im selben Untersuchungsgebiet, untersuche ich in der zweiten Studie die Anpassung von mediterranen Pflanzen entlang eines Niederschlagsgradienten, der den vorausgesagten Niederschlagsveränderungen bis zum Ende dieses Jahrhunderts entspricht. Dafür wurden die funktionellen Eigenschaften von zwei typischen mediterranen Arten in 16 Populationen gemessen. Überraschenderweise zeigten die Arten unterschiedliche Anpassungen entlang des Gradienten, dass auf eine artspezifische Anpassung an Trockenheit hinweist. Des Weiteren wird in der Studie deutlich, dass der Regengradient zwar ein wichtiger, aber kein bestimmender Faktor auf der entsprechenden Skala ist, da ein großer Anteil der intraspezifischen Merkmalsvariation innerhalb der Populationen gefunden wird. In der dritten Studie untersuche ich inwieweit Bodenfertilität die Etablierungswahrscheinlichkeit von Pflanzen mit unterschiedlichen Samenmassen direkt (durch erhöhte Nährstoffverfügbarkeit) und indirekt (durch erhöhte Konkurrenz) beeinflusst. Das Experiment wurde mit 22 Trockenrasenarten aus Nordost Brandenburg durchgeführt. Es zeigte sich, dass der positive Effekt von Samenmasse auf die Etablierungsfähigkeit abhängig von den jeweiligen Bedingungen ist und verschiedene Prozesse während der Etablierungsphase beeinflusst werden. Auf der Basis dieser Ergebnisse und Literatur, stelle ich ein konzeptionelles Model vor, dass widersprüchliche Ergebnisse aus der Literatur synthetisiert. 
Zusammengenommen zeigen die Ergebnisse meiner Dissertation, dass funktionelle Eigenschaften wichtige Erkenntnisse über die Prozesse liefern, die das Auftreten von Pflanzen und deren Anpassung entlang von Umweltgradienten bestimmen. In der abschließenden Diskussion hinterfrage ich kritisch die Verwendung von intraspezifischer Variabilität funktioneller Eigenschaften in der Gemeinschaftsökologie, Phylogenie als Surrogat für die Nische einer Art und die Standardisierung funktioneller Eigenschaften als methodische Aspekte. Abschließend gebe ich einen Ausblick über zukünftige Pflanzenökologie-Forschung mit funktionellen Eigenschaften.
KW  - functional ecology
KW  - plant community
KW  - species coexistence
KW  - biodiversity
KW  - funktionelle Ökologie
KW  - Pflanzengemeinschaften
KW  - Koexistenz von Arten
KW  - Biodiversität
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-426341
ER  -