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understanding of the field, it is necessary to increase the scale of our knowledge of its spatial, temporal, geographic, and taxonomic components. There is a disproportionate number of studies in taxonomic homogenization, with relatively few in functional homogenization, which could have greater ecological implications. Increased study into functional homogenization could give insight into conservation needs. These gaps in the literature may, however, soon be filled. The study of homogenization is increasingly gaining attention in ecological circles, with the number of studies quantifying its effects increasing exponentially between the years of 2000 and 2015.
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is overlap between these two communities, they are certainly different. However, if community two undergoes drastic change where E becomes extinct while A and B are simultaneously introduced, it now demonstrates higher species richness (greater α diversity), because there are now four species present instead of three. Yet, at the same time, communities one and two have become identical, removing any β diversity: they have homogenized. This particular trend is frequently observed in studies of biotic homogenization.
311:
298:. In urban landscapes, the introduction of non-native species such as rock doves and European starlings has led to increased homogenization of urban avian communities. Many species considered "urban exploiters" also contribute to biotic homogenization in urban environments, in part due to their ability to utilize anthropogenic resources. There have been predictions that avian taxonomic homogenization is occurring on the global scale, which could lead to future mass extinctions of
368:
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391:, the extent to which taxonomic homogenization occurs varies with taxa, country, and spatial scale. In the three European countries that were included in the study, hoverflies had homogenized in all of the countries while bees and butterflies only homogenized in two countries. The scale at which homogenization occurred also varied between taxonomic groups.
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but F and G are introduced at the same time. Community two now has greater richness and therefore greater α diversity. It also only now has one species in common with community one instead of two species. The two communities are now more different from each other than they were initially, indicating greater β diversity and therefore biotic differentiation.
218:
common misconception with taxonomic homogenization is that it represents a loss in α diversity, or that it leads to decreased species richness. However, assemblages under taxonomic homogenization may actually display an increase in α diversity, a phenomenon that has been observed in plant, animal, and microbial groups.
217:
Taxonomic homogenization is perhaps the most well-known and broadly studied component of biotic homogenization, and the two terms are often used interchangeably. It is most strictly defined as a loss in β diversity, meaning that multiple communities are increasing in taxonomic similarity over time. A
166:
can also have profound impacts on biota, leading to changes in assemblages. Natural selection and other evolutionary forces that lead to extinction can also potentially lead to homogenization. Sometimes, previously isolated populations can become exposed to each other naturally. Species interactions
123:
While it may seem counterintuitive, there are times when increased species richness (α diversity) also leads to increased homogenization. If we imagine an example of two communities: community one contains four species (A, B, C, and D). Community two contains three species (C, D, and E). While there
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Alpha diversity refers to diversity within a community: it addresses how many species are present. A community with high α diversity has many species present. Beta diversity compares multiple communities. For there to be high β diversity, two communities would have to have high α diversity but have
136:
In some cases, increased α diversity could theoretically lead to increased β diversity and differentiation. When we return to the previous example, community one still contains four species (A, B, C, and D) and community two contains three (C, D, and E). This time, C goes extinct in community two,
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are still not entirely clear and it is possible that its impacts may not be all negative. Further research is required to determine the extent of its impact on the ecosystem. However, as ecosystems become increasingly similar and simplified, there is concern that the resilience of the assemblages
272:
between North and South
America allowed previously isolated assemblages to homogenize. However, prehistoric rates of homogenization were at a far slower rate than they are currently. Additionally, organisms have been able to move far greater distances due to anthropomorphic impacts than they ever
239:
Measuring biotic homogenization ultimately requires measuring β diversity. Taxonomic homogenization is typically studied by comparing two species pools that may be separated spatially, temporally, or both. Researchers can choose to use extant pools only or pools containing both extant species and
530:
is to be successful, it is necessary to reduce the degree to which people cause invasions and extinctions. Since biotic homogenization is still a relatively new area of study, increased education about both its mechanism and impact could potentially be effective as well. If we are to improve our
441:, has led to selective extinction of certain taxa, which in turn has resulted in homogenization of certain amphibian assemblages. In addition to this more natural example of homogenization, there is evidence that there is amphibian homogenization of human-impacted environments around the world.
294:, communities have been recorded as becoming increasingly functionally similar over the course of two decades. Interestingly, in other French studies, it has been noted that there is not a temporal relationship between functional and taxonomic homogenization, a trend that had been observed in
127:
Sometimes decreased species richness can lead to greater β diversity and differentiation. If, in the example above, community one had lost species D and community two had lost species C, both communities would have lower α diversity because each would have one less species. However, the two
114:
increases (assuming no other species are simultaneously lost). Similarly, when species become extinct, species richness decreases, once again assuming no other alterations to the assemblage. As such, when there is net increase in species richness, a common misconception is to assume that
68:
Homogenization is the process of assemblages becoming increasingly similar: the reverse is the process of assemblages becoming increasingly different over time, a process known as "biotic differentiation". Just as biotic homogenization has genetic, taxonomic, and functional components,
35:. While the term is sometimes used interchangeably with "taxonomic homogenization", "functional homogenization", and "genetic homogenization", biotic homogenization is actually an overarching concept that encompasses the other three. This phenomenon stems primarily from two sources:
226:
Functional homogenization refers to the increase in similarity of function across a community: that is, similarity in the roles filled by the species. In an ecosystem that has undergone functional homogenization, there are increased species that fill the same functional role or
1049:
Carvalheiro LG, Kunin WE, Keil P, Aguirre-Gutiérrez J, Ellis WN, Fox R, Groom Q, Hennekens S, Van
Landuyt W, Maes D, Van de Meutter F, Michez D, Rasmont P, Ode B, Potts SG, Reemer M, Roberts SP, Schaminée J, WallisDeVries MF, Biesmeijer JC (July 2013). Buckley Y (ed.).
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were studied at both a global and local scale over a span of forty years, ending in 2005. On a global scale, it was found that homogenization had increased by 2%, and that introductions contributed more to this change than did extinctions. In a more localized study in
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Decreased richness could also lead to homogenization. If A were to go extinct in community one and E were to go extinct in community two, then both communities would have lower richness, since they both would be out one species. There would also be greater overlap in
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Genetic homogenization refers to the underlying molecular processes involved in biotic homogenization. It typically results from hybridization with non-native species, leading to decreased variation in the gene pool. These hybridization events may be either
161:
Homogenization can result from either anthropomorphic or natural pressures. Many cases of species introductions are the result of either unintentional or intentional introduction of species by humans, be it for the pet trade, recreation, or agriculture.
201:, which is accomplished through a comparison of how common specific genotypes are. If an allele occurs at a similar frequency between two populations, then there is greater homogenization present. Other evolutionary forces such as
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differentiation has occurred. This, however, may or may not be the case. While an increase in species richness does indicate an increase in α diversity, homogenization and differentiation specifically address β diversity.
355:, where freshwater systems support diverse assemblages of endemic fishes. In a comparison of 201 watersheds that analyzed changes in similarities over 200 years, approximately 65% of comparisons demonstrate that the
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Freshwater fishes were among the first taxonomic groups to be used in homogenization studies, and trends have been observed on several continents. Homogenization in freshwater fishes typically stems from
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against stressful events will be limited. Indeed, the more limited an assemblage becomes on functional, taxonomic, and genetic levels, the more constrained that assemblage is in its ability to
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has been connected to an increase in α diversity but a decrease in β diversity of bacteria. This trend is likely due to the loss of endemic species that have limited ranges being replaced by
47:
record, and still occurs due to natural impacts, it has recently been accelerated due anthropogenic pressures. Biotic homogenization has become recognized as a significant component of the
658:
Villéger S, Grenouillet G, Brosse S (December 2014). "Functional homogenization exceeds taxonomic homogenization among
European fish assemblages: Change in functional β-diversity".
290:. Certain island studies have demonstrated that on a small spatial scale, that avian taxonomic homogenization occurs far more rapidly than it does on a larger spatial scale. In
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increasing over the course of human history. Additionally, there have been significantly more introductions on the continental scale than there have been extinction of
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acts on diversity between individuals and species, and if that diversity does not exist, communities are severely limited when it comes to future evolutionary paths.
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Limiting biotic homogenization ultimately relies on limiting its sources: species invasion and extinction. Because these are largely rooted in human activity, if
457:, increasing overall species richness and α diversity. However, β diversity has decreased in some circumstances, resulting in homogenization effects.
737:
Olden JD, Leroy Poff N, Douglas MR, Douglas ME, Fausch KD (January 2004). "Ecological and evolutionary consequences of biotic homogenization".
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Smith KG, Lips KR, Chase JM (October 2009). "Selecting for extinction: nonrandom disease-associated extinction homogenizes amphibian biotas".
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reconstructed historical species. It is not unusual to compare relationships between α diversity and β diversity in a population.
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is an ungulate in South Africa. Ungulates have been homogenizing at a greater rate in South Africa than they have been globally.
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compared to other taxonomic groups, there is evidence that it exists in multiple taxa. According to a 2015 study that examined
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Smith KG (January 2006). "Patterns of nonindigenous herpetofaunal richness and biotic homogenization among
Florida counties".
505:. Due to the fact that the study of biotic homogenization is still relatively new, the implications of homogenization on the
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communities would have no species in common, which would dramatically increase the β diversity, leading to differentiation.
962:"No fry zones: How restaurant distribution and abundance influence avian communities in the Phoenix, AZ metropolitan area"
399:
811:
Spear D, Chown SL (2008). "Taxonomic homogenization in ungulates: patterns and mechanisms at local and global scales".
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865:"Conversion of the Amazon rainforest to agriculture results in biotic homogenization of soil bacterial communities"
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Alpha diversity describes diversity within a population; beta diversity describes diversity between populations.
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406:
1052:"Species richness declines and biotic homogenisation have slowed down for NW-European pollinators and plants"
330:, homogenization increased by 8%. In this example, species richness increased as homogenization increased.
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Urbanization changes species conformation in a habitat, and it can be a driving force in homogenization.
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153:
1124:"Phylogenetic homogenization of amphibian assemblages in human-altered habitats across the globe"
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20:
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Rodrigues JL, Pellizari VH, Mueller R, Baek K, Jesus E, Paula FS, et al. (January 2013).
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Agriculture in the Amazon River Basin (pictured above) has led to homogenization of bacteria.
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1014:, Brooks TM, Mckinney ML (February 2000). "Taxonomic homogenization of the global avifauna".
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Community composition, rather than richness, plays the more crucial role in maintaining the
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Brown JA, Lerman SB, Basile AJ, Bateman HL, Deviche P, Warren PS, Sweazea KL (2022-10-19).
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is parasitic to amphibians, and has led to homogenization of amphibians in
Central America.
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of nonnative species. While this process pre-dates human civilization, as evidenced by the
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between the two communities, indicating lost β diversity and increased homogenization.
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Anthropomorphic impacts on plants have been complex, with overall species richness of
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Understanding homogenization requires an understanding of the difference between
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Proceedings of the
National Academy of Sciences of the United States of America
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Proceedings of the
National Academy of Sciences of the United States of America
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has not led to homogenization of reptilian communities in
Florida. However, in
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1183:"The Homogocene: a research prospectus for the study of biotic homogenisation"
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777:"Evaluating taxonomic homogenization of freshwater fish assemblages in Chile"
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698:"Biotic homogenization: a new research agenda for conservation biogeography"
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Nowakowski AJ, Frishkoff LO, Thompson ME, Smith TM, Todd BD (April 2018).
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Both taxonomic and functional homogenization have been investigated in
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are introduced to a habitat, be it naturally or artificially, overall
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There has been relatively little research on homogenization in the
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differentiation can occur at any of these levels of organization.
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While there have been fewer studies of biotic homogenization in
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Most studies of biotic homogenization have typically focused on
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examples of biotic homogenization. For example, the
Panamanian
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Hoverflies have become taxonomically homogenized in Europe.
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become increasingly similar over time. This process may be
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is the process by which two or more spatially distributed
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Vargas PV, Arismendi I, Gomez-Uchida D (December 2015).
351:. In a more specific example, there was a 2015 study in
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131:
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can also cause local extinctions, be the relationship
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197:. Genetic homogenization can be analyzed in terms of
51:, and as such has become of increasing importance to
627:"On defining and quantifying biotic homogenization"
419:, and according to a 2006 study, introduction of
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577:. John Wiley & Sons, Ltd. pp. 1–8.
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209:can also lead to genetic homogenization.
1181:Olden JD, Comte L, Giam X (2018-06-03).
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64:Homogenization versus differentiation
132:Negative relationships with richness
119:Positive relationships with richness
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583:10.1002/9780470015902.a0020471.pub2
149:Pressures leading to homogenization
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1028:10.1111/j.1469-1795.2000.tb00084.x
625:Olden JD, Rooney TP (March 2006).
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739:Trends in Ecology & Evolution
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264:The fossil record gives multiple
939:10.1111/j.1461-0248.2009.01363.x
825:10.1111/j.1365-2699.2008.01926.x
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359:are undergoing homogenization.
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407:Batrachochytrium dendrobatidis
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73:Alpha and beta diversity
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1103:. 127: 3 (3): 327–335.
1101:Biological Conservation
890:10.1073/pnas.1220608110
813:Journal of Biogeography
702:Journal of Biogeography
437:which is pathogenic to
395:Amphibians and reptiles
53:conservation ecologists
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21:ecological communities
497:Ecology and Evolution
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17:Biotic homogenization
96:species compositions
1140:2018PNAS..115E3454N
1134:(15): E3454–E3462.
1016:Animal Conservation
881:2013PNAS..110..988R
403:The chytrid fungus
199:allelic frequencies
143:species composition
91:beta (β) diversity.
49:biodiversity crisis
478:Amazon river basin
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207:bottleneck effects
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94:different, unique
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33:beta (β) diversity
1068:10.1111/ele.12121
819:(11): 1962–1975.
708:(12): 2027–2039.
672:10.1111/geb.12226
666:(12): 1450–1460.
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347:fishes for
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266:prehistoric
37:extinctions
535:References
486:generalist
439:amphibians
385:hoverflies
357:watersheds
222:Functional
179:Components
173:pathogenic
1209:1314-2488
1193:: 23–36.
503:ecosystem
488:species.
421:nonnative
345:nonnative
323:Ungulates
213:Taxonomic
169:predatory
108:organisms
87:alpha (α)
41:invasions
29:taxonomic
1223:Category
1187:NeoBiota
1168:29555733
1086:23692632
1036:86637245
998:36260638
966:PLOS ONE
947:19694784
909:23271810
843:85768359
759:16701221
724:35763633
482:tolerant
455:endemics
424:reptiles
341:stocking
300:avifauna
244:Examples
235:Analysis
59:Overview
1159:5899437
1136:Bibcode
1077:3738924
989:9581420
900:3549139
877:Bibcode
476:in the
377:insects
363:Insects
316:Gemsbok
306:Mammals
277:Animals
184:Genetic
25:genetic
1207:
1166:
1156:
1084:
1074:
1034:
996:
986:
945:
907:
897:
841:
757:
722:
589:
512:evolve
445:Plants
387:, and
334:Fishes
292:France
250:fishes
45:fossil
1032:S2CID
839:S2CID
787:(1).
720:S2CID
451:flora
353:Chile
288:birds
282:Birds
229:niche
106:When
1205:ISSN
1164:PMID
1082:PMID
994:PMID
943:PMID
905:PMID
755:PMID
587:ISBN
381:bees
314:The
252:and
205:and
89:and
1195:doi
1154:PMC
1144:doi
1132:115
1105:doi
1072:PMC
1064:doi
1024:doi
984:PMC
974:doi
935:doi
895:PMC
885:doi
873:110
829:hdl
821:doi
789:doi
747:doi
710:doi
668:doi
639:doi
579:doi
575:eLS
343:of
193:or
171:or
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