Competition among invasive and endemic carrion fly species in the Galapagos Islands with implications for biological control risk assessment

The composition of the necrobiome community in the Galapagos Islands is poorly understood, and nothing is known about the dynamics between endemic species and those introduced through human activity. To determine the composition of the carrion fly community, specifically members of the families Muscidae, Calliphoridae and Sarcophagidae, we deployed four kinds of carrion bait traps during the cool and hot seasons at two lowland and two highland sites on Santa Cruz Island within the Galapagos archipelago. We also conducted a laboratory experiment to assess resource competition between fly species encountered in the baiting study. Of the eight fly species found in our baited traps, all were introduced except for the endemic sarcophagid, Sarothromyiops dasycnemis. Four endemic and one native carrion‐feeding species that had been previously recorded on this island were not found. The introduced sarcophagid, Peckia chrysostoma, was the most abundant fly species, comprising over half of the collected specimens, and it was highly dominant at the lowland sites. The endemic species, S. dasycnemis, was only recorded at the lowland sites during the hot season. On the other hand, the calliphorid species were dominant at the highland sites. Experiments demonstrated that P. chrysostoma is a strong competitor against other carrion fly species in the Galapagos necrobiome, including the endemic S. dasycnemis. A comparison of our data with historical records, combined with the results of our laboratory study, leads to the conclusion that introduced carrion fly species, such as P. chrysostoma, represent a threat to endemic carrion fly species, such as S. dasycnemis. Three parasitoid species were reared from 19% of the collected fly puparia. Two of these species attacked fly larvae (Brachymeria podagrica and Aphaereta sp.), whereas one species attacked fly puparia (Exoristobia sp.) We discuss our results in light of the possibility of the purposeful introduction of a parasitoid as a biological control agent against the avian vampire fly (Philornis downsi; Diptera: Muscidae) in Galapagos.

of carrion bait traps during the cool and hot seasons at two lowland and two highland sites on Santa Cruz Island within the Galapagos archipelago.We also conducted a laboratory experiment to assess resource competition between fly species encountered in the baiting study.
3. Of the eight fly species found in our baited traps, all were introduced except for the endemic sarcophagid, Sarothromyiops dasycnemis.Four endemic and one native carrion-feeding species that had been previously recorded on this island were not found.The introduced sarcophagid, Peckia chrysostoma, was the most abundant fly species, comprising over half of the collected specimens, and it was highly dominant at the lowland sites.The endemic species, S. dasycnemis, was only recorded at the lowland sites during the hot season.On the other hand, the calliphorid species were dominant at the highland sites.
4. Experiments demonstrated that P. chrysostoma is a strong competitor against other carrion fly species in the Galapagos necrobiome, including the endemic S. dasycnemis.

5.
A comparison of our data with historical records, combined with the results of our laboratory study, leads to the conclusion that introduced carrion fly species, such as P. chrysostoma, represent a threat to endemic carrion fly species, such as S. dasycnemis.
6. Three parasitoid species were reared from 19% of the collected fly puparia.Two of these species attacked fly larvae (Brachymeria podagrica and Aphaereta sp.), whereas one species attacked fly puparia (Exoristobia sp.)

INTRODUCTION
Competition among insect species is frequent and can be particularly intense on short-lived, limited and unreliable resources.Decomposing dead animals, or carrion, represent a transient natural resource that is associated with intense competition within and among consumer species (Carmo et al., 2018;Weatherbee et al., 2017).The biota that depends on carrion, or the 'necrobiome' (Benbow et al., 2013), includes a number of invertebrate taxa that can interact as competitors and/or predators during the larval stages (Benbow et al., 2019;Komo et al., 2021;Prinkkilá & Hanski, 1995).Carrion flies are crucial decomposers in the necrobiome, especially flies in the families Calliphoridae, Sarcophagidae and Muscidae as they are consistently the most commonly encountered necrophagous taxa (Kuusela & Hanski, 1982;Merritt et al., 2015;Ren et al., 2018).
These flies play a vital role in breaking down and converting dead organic matter into nutrients, which they then disperse for use by other trophic levels (Benbow et al., 2019;Merritt et al., 2015;Szpila et al., 2015).The loss of these services can lead to adverse effects on the environment or human health (Barton et al., 2013;Carter et al., 2007).
Necrobiome communities are vulnerable to a variety of processes that affect their component species.In particular, biological invasions can lead to the loss or reduction of populations of native species (Brundage et al., 2014;Carmo et al., 2018;Gessner et al., 2010;Spencer et al., 2020).The effects of biological invasions can be especially strong in island ecosystems where invasive species may outcompete resident species (Causton et al., 2006;Simberloff, 2010;Spatz et al., 2017).The Galapagos Archipelago, located 1000 km from mainland Ecuador, supports at least nine endemic and two native species belonging to the most common necrophagous Diptera families Sarcophagidae, Calliphoridae and Muscidae, in addition to 21 introduced, two cryptogenic (i.e., possibly native or introduced) and three taxonomically undetermined species from these same families (Sinclair, 2023).The role of endemic and native fly species as carcass decomposers in Galapagos is understudied, with little information on larval feeding habits, but at least eight species are suspected carrion feeders: Lucilia pionia (Walker), L. setosa (James) (Diptera: Calliphoridae), Blaesoxipha insularis (Townsend), B. isla (Curran), B. violenta (Walker), B. williamsi (Curran), Sarothromyiops dasycnemis (Thomson) and Galopagomyia inoa (Walker) (Diptera: Sarcophagidae).
In addition to these species, at least 12 of the 21 species of flies from these families that have been introduced to Galapagos are known or suspected to be part of the local necrobiome (Sinclair, 2023).Studies are needed to better understand the fly fauna associated with the Galapagos necrobiome and any interspecific relationships that exist between them.
Given the rapid pace of species introductions in the Galapagos Islands over the past decades (Causton et al., 2006;Toral-Granda et al., 2017), a particularly important question involves the potential displacement of endemic species by introduced species.
An additional reason for studying the necrobiome fly composition and the families mentioned above is that information on these families (Muscidae, Sarcophagidae and Calliphoridae) is relevant to the management of an introduced fly of particular importance, the avian vampire fly (Philornis downsi Dodge & Aitken, Diptera: Muscidae).The avian vampire fly is an invasive bird parasite that causes high nestling mortality in at least 20 endemic landbird species in Galapagos (Fessl et al., 2018;Kleindorfer & Dudaniec, 2016;McNew & Clayton, 2018).
Biological control has been deemed the most promising long-term solution for controlling this fly (Fessl et al., 2018) and the parasitoid wasp Conura annulifera (Walker) (Hymenoptera: Chalcididae), a purported specialist of flies in the genus Philornis Meinert (Bulgarella et al., 2017;Ramirez et al., 2022), is considered a promising agent (Boulton et al., 2019;Boulton & Heimpel, 2017).Although the avian vampire fly does not play a direct role in the necrobiome, the introduction of C. annulifera or other parasitoids could pose a threat to endemic and native carrion flies due to their relatedness to the avian vampire fly and could, thus, affect the composition of the local necrobiome and critical ecological services such as carcass decomposition.
Here, we report on the composition and abundance of fly species associated with carrion, including introduced, endemic and native species in Santa Cruz Island, Galapagos.We also use a laboratory experiment to characterise competition between the most abundant introduced carrion fly species, Peckia chrysostoma Wiedemann (Diptera: Sarcophagidae), and other necrophagous fly taxa including the endemic S. dasycnemis.Finally, we report on resident parasitoids of larval and puparial stages of carrion flies.

Locations
Sampling and fly collection were done in four distinct areas of Santa Cruz Island in Galapagos from late June to August and from October to early November 2021 (during the cool season), and from February to early May 2022 during the hot season (Trueman & d'Ozouville, 2010).

Collection and rearing of carrion flies
Four varieties of carrion substrates, raw beef, fish, chicken meat and broken chicken eggs, were used as bait ($500 g) for the sampling.The meat from all animal sources was not ground and contained fat, skin and bone.To deploy the substrates, we used cardboard cylindrical containers, locally known as 'tarrinas' (10 cm diameter and 12 cm height), with a perforated lid (1 cm holes), enveloped in metal chicken wire to prevent access by vertebrate scavengers and a plastic roof for rain protection (see Figure S1).Each of the four substrates was tested once each month at each of the four locations.Only one type of substrate was deployed at a time.The containers were deployed every Monday and left in the field for 72 h as our goal was to obtain fly larvae weekly for the length of our studies.After the allotted time in the field, the containers were placed on top of rectangular foil pans (22 cm Â 30 cm) containing 5 cm of sifted soil, which were placed within mesh cages (30 cm Â 30 cm Â 30 cm).All mesh cages were kept at ambient temperature, humidity and photoperiod inside a wood-frame structure with mesh and chicken wire walls and a galvanised roof.This building was located at the El Barranco site.Fully developed, post-feeding larval dispersal was observed, and third-instar larvae crawled out of their containers, dug and pupated within the soil, with pupation occurring 1-2 days later.On the third day, the soil in each tray was sifted, and the puparia were collected and placed in cardboard cylindrical containers (6 cm diameter and 6 cm height) with a mesh lid secured by a rubber band, to wait for insect eclosion.Adult flies and parasitoids emerged from these puparia, and we considered that any emerging parasitoids had attacked the flies during the larval stage.After eclosion, adult flies

Insect colonies
Single-species colonies initiated with emerged flies were established with the purpose of controlling the stage and age of flies that were used in our other experiments.Previously identified flies (see above) were placed into individual mesh cages similar to those described above, one species per cage, and the cage was furnished with an aluminium tray with sifted soil and a container similar to the ones used to deploy substrates in the field.Beef meat and fat ($350 g) was placed in the containers and replenished weekly.
Adult flies were provided water and granulated sugar at libitum within the cages, and misted with potable water twice a day.All colonies were kept at ambient temperature, humidity and photoperiod in the building described above.The soil was sifted every 4 days to extract puparia and dispersing third-instar larvae.We used the puparia to survey pupal parasitoids (see below) and the third-instar larvae for other experiments and colony growth.

Survey for pupal parasitoids
Thirty puparia of a mix of different fly species taken from the colonies described above were deployed in the field in the same types of containers used to attract flies.These were set alongside the fly baits for 72 h.The species of deployed puparia varied depending on availability, but all containers included puparia of P. chrysostoma, P. lambens, L. eximia and H. aenescens (in both seasons) and S. dasycnemis puparia during the hot season.After 72 h, the puparia were recovered and placed into individual emergence vials to allow for fly or parasitoid emergence.

Competition experiment
This experiment assessed whether the larvae of P. chrysostoma, the most abundant carrion fly species found in bait containers (see Results), would outcompete larvae of the other fly species in a controlled setting using methods adapted from Ferraz (1993).Females from the following species were taken from our colonies and placed into single-species containers with 1-day-old decomposing meat for oviposition: P. chrysostoma, P. lambens, S. dasycnemis, L. eximia and H. aenescens.Oviposition occurred within the first 30 h.Groups of 10 first-instar larvae of a given species were transferred to petri dishes (60 Â 15 mm) containing 10 g of raw ground beef along with 10 first-instar larvae of P. chrysostoma.Petri dishes with 20 first-instar larvae of either P. lambens, L. eximia, S. dasycnemis or H. aenescens served as controls.The petri dishes with the ground beef and the larvae were placed inside a container as described above ('tarrina'), with a 10-cm layer of sifted soil, which served as a pupation medium for post-feeding larval dispersal.The treatments and controls were carried out simultaneously under ambient conditions averaging temperatures of 26.19 C (±2.822 SD) and humidity of 86.55% (±7.732SD).
The larvae were left for 7 days after which puparia were sifted from the soil and counted.The puparia were then transferred to emergence containers similar to the containers mentioned above.

Statistical analyses
All statistical analyses were performed in R-studio (RStudio Team, 2023) including a one-way analysis of variance (ANOVA) to determine if there were bait preferences and a post-hoc Tukey test to compare among them.Species accumulation curves for the different seasons and baits were generated using the R package 'vegan' with Michaelis-Menten asymptotic curves fitted to the data for each graph.To detect the effects of the abundance of introduced flies and parasitoids on the endemic S. dasycnemis in the field sampling study, we used generalised linear models (GLMs) with Quasi-Poisson error structure implemented in the R package 'lme4'.We only used data gathered at the two lowland sites (littoral and arid) during the hot season, as S. dasycnemis was only found at these locations during that period of time.In the first analysis, the number of eclosing S. dasycnemis adults emerging per container was the dependent variable and the numbers of eclosing adults of each of the five introduced fly species were the independent variables.In the second analysis, the effect of the number of fly puparia from which parasitoids emerged (pooled over fly species) on the number of S. dasycnemis adults eclosing per container was estimated for the two parasitoid species that were found in the range of S. dasycnemis.For both analyses, we used variation inflation factors to detect multicollinearity among the species used as independent variables in the R program 'car'.For the competition experiment, we compared the abundance of puparia of P. chrysostoma versus the other fly species using t-tests.The species accumulation curves suggest that our finding of eight fly species was approximately five below the expected asymptote of 13 ± 2.351 (SD) species based on the Michaelis-Menten relationship (Figure 2a).The observed species richness during the hot season reached the expected asymptote of 7 ± 0.938 (SD), whereas the observed species richness of 5 during the cool season underestimated an expected asymptote of 10 ± 1.484 species (SD; Figure 2b,c).All bait types attracted between five and eight fly species, with accumulation curves indicating the maximum number of species for specific substrates: chicken (observed = 8, expected = 14 ± 2.088 SD), eggs (observed = 5, expected = 7 ± 1.184 SD), fish (observed = 6, expected = 10 ± 1.760 SD) and beef (observed = 8, expected = 9 ± 1.750 SD) attracted eight species (Figure 2d-g).

Location and seasonality
The GLM analyses found a significant positive correlation between the abundance of P. lambens and the endemic species S. dasycnemis, but no other significant correlations were observed (Table 2 and Figure 3).

Parasitoid emergence
From the 3337 fly puparia collected from the field, a total of 642 yielded parasitoids, representing three different species (Table 1) pupae attacked by this wasp), followed by P. lambens (21%), and S. dasycnemis (1%).This parasitoid was found parasitizing 26.4% of the P. chrysostoma puparia collected (Table 1).The second most abundant parasitoid, Exoristobia sp., attacked only P. chrysostoma in the Scalesia zone (n = 6; representing 86% of all Exoristobia sp.reared) and P. lambens (n = 1; 14%) in the littoral zone.Both of these host species were attacked as puparia during the cool season.Finally, the parasitoid Aphaereta sp.emerged from a single L. eximia puparium; the fly was exposed to this parasitoid as a larva in the Miconia zone during the cool season.To our knowledge, this is the first published report of a species in the genus Aphaereta in Galapagos.
The GLM analyses found a significant positive correlation between the endemic fly, S. dasycnemis and abundance of the larval parasitoid wasp, B. podagrica (Table 2 and Figure 3).

Experimental competition assays
Larvae of all of the fly species in the interspecific competition experiment experienced significantly greater levels of mortality when paired with P. chrysostoma than when paired with equivalent numbers of F I G U R E 3 Scatterplots of abundance of flies and parasitoids (x-axis) that were found in the habitat of the endemic fly Sarothromyiops dasycnemis (y-axis).Linear regression lines were fitted to the graphs for flies (blue) and parasitoids (green).The Michaelis-Menten relationship models suggest that we captured more than half of the available carrion fly species at our study sites.Among the species that were not collected but that were expected at our field sites are four endemic and one native species that are likely associated with carrion and that have been documented on Santa Cruz Island (Sinclair, 2023).These species are the sarcopha-   and L. deceptor.The absence of these fly species in our traps may be attributed to several factors including temporary absence during our sampling period, the stage of carrion decomposition, bias towards non-natives instead of natives in our baits, non-carrion feeding habits or displacement by introduced species, such as P. chrysostoma.It is also possible that these species are specialised on carrion originating in Galapagos, and that they are reluctant to colonize our baits, three of which were sourced from introduced species (beef, chicken and eggs).Such a scenario is possible for G. inoa, the larvae of which have been reported feeding on eggs of native sea turtles and eggs and carcasses of endemic land tortoises and sea lions (Román et al., 2023;Sinclair, 2023;S. Aguirre, unpublished).However, it should also be noted that the Galapagos Islands have been subjected to multiple introductions of non-native species, including cattle and chickens, over the past 200 years (Hickman, 1985), so that these bait sources should not be completely novel to carrion flies.In addition, a separate study including endemic Galapagos lizards and passerine birds did not yield a higher proportion of endemic versus introduced carrion flies (C.Lehnen, pers. comm.).
Taken together, our results provide support for the displacement hypothesis for at least some endemic species and suggest a shift in the composition of the dipteran community on Santa Cruz Island from historical records.Lopes (1978)  In our studies, P. chrysostoma was the dominant sarcophagid species on this island (55% of the total number of flies reared in bait traps), compared with the endemic S. dasycnemis at 3.9%, and was especially dominant in the baits set out in the littoral and arid zones, making up 68% and 58% of the carrion flies, respectively.
P. chrysostoma is a forensically important flesh fly native to South America and it is commonly found in decaying human corpses.It was first recorded in Galapagos in 1935 (Causton et al., 2006) and its prevalence on Santa Cruz Island is consistent with the findings in its native range, especially in Brazil, where P. chrysostoma was found to be the most common fly species on carrion (d'Almeida, 1984;Dias et al., 1984;Lopes, 1973;Tavares et al., 1988).In addition, Ferraz (1993) demonstrated that P. chrysostoma is a strong competitor under controlled conditions and suggested that its salivary secretions or metabolic waste could aid in creating a toxic environment for competing species.Another hypothesis for the success of P. chrysostoma is that it inhibits oviposition and larviposition by other fly species.(Bradley & Sheppard, 1984).
S. dasycnemis was the only endemic carrion-feeding fly species encountered in our study, and it was found in 12% of our baits during the hot season, but not at all during the cool season.Notably, it was only found at the lowland sampling sites, placing it in direct contact with P. chrysostoma, which was dominant in the traps at these sites.
Both lowland sampling sites were near Puerta Ayora, the most populated town on Santa Cruz Island, with an estimated 12,000 inhabitants (Toral-Granda et al., 2017).The presence of S. dasycnemis near human settlements may reflect the adoption of synanthropic (human-associated) behaviour in this species as well as a broad feeding range.The presence of S. dasycnemis may have been partially enabled by protection through parasitism of its main competitor, P. chrysostoma.The parasitoid, B. podagrica, was the most abundant species attacking carrion flies in our study and emerged mostly from P. chrysostoma.This parasitoid tends to prefer larger larvae as hosts (Delvare & Huchet, 2017;Roberts, 1933) and P. chrysostoma produced the largest larvae of all the carrion flies collected (I.E.R., unpublished).
Our findings that the necrobiome of the Galapagos Islands is dominated by introduced species has implications for understanding potential interactions between the necrobiome community and any biological control agent that might be released against other fly species, such as the avian vampire fly, P. downsi.One proposed biological control agent of P. downsi, the wasp C. annulifera, is an obligate parasitoid of cyclorrhaphan fly puparia that appears to specialise on Philornis species (Bulgarella et al., 2017;Ramirez et al., 2022).All fly species collected in this study were cyclorrhaphans and, thus, potential hosts of C. annulifera (Boulton & Heimpel, 2018).However, our studies suggest that competition with introduced fly species may be a far greater threat to the survival of endemic or native carrion flies than the release of C. annulifera would be.Furthermore, the pupation behaviour of many insects including carrion flies (introduced, native and endemic species) would likely protect them from pupal parasitoids, as it usually takes place underground (Frederickx et al., 2014).Indeed, in this study, we observed that the endemic S. dasycnemis larvae burrow underground to pupate (I.E.R., unpublished).
Carrion-feeding species could be at risk from a parasitoid introduction against P. downsi if they are found in bird nests with dead nestlings.
In its native range of mainland Ecuador, C. annulifera shows a strong association with bird nests, particularly those containing puparia of Philornis spp.(Ramirez et al., 2022).Little is known about the prevalence of carrion flies in bird nests in the Galapagos Islands and directed surveys are required to determine whether nests are frequented by endemic or native species.To date, the only endemic species found in nests with dead chicks is B. insularis, reported in nests of Geospiza fortis and G. fuliginosa at two locations on Santa Cruz Island in 2004 (B. Fessl, pers. comm).On the other hand, reports of introduced carrion flies are more common.For example, Fessl and Tebbich (2002) found the introduced P. lambens (as Sarcodexia lambens) in 34 of 177 wild bird nests surveyed on Santa Cruz Island and in a subsequent study Fessl et al. (2006) were identified as species by A.K.T. and B.J.S., and the parasitoids were identified as genus by Dr. John Luhman from the University of Minnesota, Department of Entomology Insect Collection.Exemplars of reared fly and parasitoid specimens are housed in the Charles Darwin Research Station Terrestrial Invertebrates Collection (ICCDRS).
Figure1]).Seven fly species were recorded in the lowlands, with a greater diversity and abundance of Sarcophagidae than Calliphoridae or Muscidae in the littoral zone (97% of abundance) and the arid zone (92% of abundance).In the highlands, six species were recorded with Calliphoridae being more abundant than Sarcophagidae or Muscidae in the Miconia zone (46%) and the Scalesia zone (64%) (Figure1).Some species were found only in the lowland habitats (S. dasycnemis and H. aenescens) and others were found almost exclusively in the highlands (C.albiceps and C. megacephala).Only a single species was found in roughly equal proportions at all sites (P.lambens).All other species were found in both the lowland and highland habitats but varied in : Brachymeria podagrica (Fabricius) (Hymenoptera: Chalcididae, n = 634 puparia containing B. podagrica, representing 98.8% of all parasitoids reared), Exoristobia sp.(Hymenoptera: Encyrtidae, n = 7 puparia, 1.1%) and Aphaereta sp.(Hymenoptera: Braconidae, n = 1 puparium, 0.2%).B. podagrica was found in both seasons and at all locations and baits, emerging exclusively from puparia that had been collected from the field as larvae.Based on puparium morphology, we determined that B. podagrica attacked only sarcophagid flies with P. chrysostoma being the most common host (78% of all F I G U R E 2 Species accumulation curves for Santa Cruz Island based on the seasonality and bait types.The black line represents the species accumulation, and the grey lines demonstrate the Michaelis-Menten asymptotic curve (y = Vm Â x/(K + x)) where Vm represents the asymptote of the number of species and K represents the number of deployed baits associated with ½ of the value of Vm.
T A B L E 1 The total number of parasitoids eclosing from the puparia of the eight carrion fly species reared in this study with the proportion of fly puparia parasitized in parentheses.their species (Figure4): H. aenescens (t = À6.989,p = < 0.0001, df = 17.015),L. eximia (t = À9.043,p = < 0.0001, df = 9.918), P. lambens (t = À16.2,p = < 0.0001, df = 14.169) and S. dasycnemis (t = À9.774,p = < 0.0001, df = 12.76).DISCUSSIONOf the eight fly species reared in our baited traps on Santa Cruz Island, all are listed as having been introduced to Galapagos through human activity except for the endemic sarcophagid S. dasycnemis.The sarcophagids P. chrysostoma and P. lambens dominated the bait traps in the lowlands, and the calliphorids were the most abundant in the traps in the highlands.The most abundant species overall was P. chrysostoma, which made up over half of the fly individuals collected and was present in almost all baits during both seasons.Furthermore, we experimentally showed that the presence of this species in carrion induced mortality in the larvae of four other fly species, including the endemic S. dasycnemis.Given the information collected in this study, we concluded that P. chrysostoma outcompetes other carrion fly species in the Galapagos necrobiome and recommend that P. chrysostoma be assigned the status of invasive species in the Galapagos Islands per the definition of the International Union for the Conservation of Nature (IUCN, n.d).
gids B. insularis, B. violenta and G. inoa and the calliphorids L. pionia T A B L E 2 Results of generalized linear models with Quasi-Poisson error structure investigating the effect of abundance of fly and parasitoid species on the abundance of the endemic fly, Sarothromyiops dascynemis.
Data were only gathered from lowland sites during hot season.See text for details of the analyses.(*P<0.05,**P<0.01,***P<0.001).F I G U R E 4 Bar plots for the results of the competition experiment in which the percentage of pupae of four fly species is shown for treatment and control exposures.'Treatment' indicates the presence of Peckia chrysostoma larvae while 'Control' indicates the presence of only the indicated species.Gray lines represent the standard error of the mean.[Correction added on 08 January 2024, after first online publication: The y axis has been corrected.] reported that S. dasycnemis (as Sarothromyiops canus Townsend) was the most common sarcophagid species in samples that he identified from the archipelago.He also reported identifying specimens of G. inoa, B. violenta and B. insularis that were collected on Santa Cruz Island in 1964.To our knowledge, In summary, this research contributes novel information on the necrobiome community in Galapagos.In particular, we highlight the prevalence of introduced carrion flies and the notable paucity of endemic or native carrion fly species within the necrobiome on Santa Cruz Island.We suggest that endemic and native carrion flies have been outcompeted and displaced by introduced species, notably P. chrysostoma, which we consider to be invasive in the Galapagos Islands.Joselyn Yar: Investigation; conceptualization; methodology; writingreview and editing.Bradley J. Sinclair: Investigation; validation; writingreview and editing.Ana K. Torres Donoso: Investigation; methodology; writingreview and editing; formal analysis; validation.