Literature review: Impact of Chilean needle grass ... - Weeds Australia

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The suitability of a new habitat for a particular invader is known as the ‘invasibility’ of the habitat: “the properties of the region of introduction that facilitate the survival of non-indigenous species” (Gassó et al. 2009 p. 51). Enemy release and biotic resistance ‘Enemy release’ theory postulates that an exotic plant becomes a successful invader because it lacks co-evolved natural enemies and plant competitors in its introduced range: it is ‘released’ from the effects of specialist predators, parasites and plant antagonists of its native environment, and is much less subject to herbivory in the introduced range, the native generalist predators being better adapted to, and preferentially consuming native plants (Keane and Crawley 2002, Levine et al. 2004, Parker et al. 2006a). Reduced control by natural enemies in the invaded areas is believed to enable the plant to be more productive and more reproductively successful, and for its populations to expand. ‘Biotic resistance’ or ‘diversity-resistance’ theory posits that some combination of biological effects of the native organisms regulate the success of the exotic plant, although they seldom prevent invasions (Levine et al. 2004). The original idea is attributed to Elton (1958) who proposed that the greater the species-richness of a community, the more resistant to invasion it should be. More intense competion for resources and consequent fuller resource sequestration in more diverse communities is the explanation usually invoked, either due to a combined effect of all the species, or the greater likelihood that a species or functional group competitive with the invader is present in diverse communities (Symstad 2000, Dukes 2002, Stohlgren 2007). Early attempts to test the theory through analysis of plant diversity at a mix of spatial scales (e.g. the meta-analysis by Lonsdale 1999) provided a confused picture and mostly showed correlations of high native plant species richness with high exotic richness. But recent consensus is that biotic resistance functions very differently at different spatial scales. A majority of plant diversity studies and experiments at small spatial scales (patch, plant association) and some modelling support the theory (Prieur- Richard and Lavorel 2000, Symstad 2000, Dunstan and Johnson 2006) but at larger spatial scales there is generally a marked positive correlation between plant species richness and invasibility that corresponds to increased environmental (landscape, regional, continental) heterogeneity (Knight and Reich 2005, Dunstan and Johnson 2006). However Stohlgren (2007) argued that even at the small scale (1 m 2 ) contradictory results have been found, suggesting that environmental factors other than the plant diversity of an invaded area may frequently be of greater importance in determining invasibility. Enemy release theory is focused on plant diseases and the invertebrate consumers of plants, more or less ignoring the possibility that native plants in the invader’s area of origin may have similar negative impacts. In that context, to explain a particular successful plant invasion, the enemy release hypothesis requires that the plant’s specialist natural enemies in the native range are absent from the introduced range, that specialist enemies in the introduced range do not shift onto the potential new host, and that the generalist enemies in the introduced range have less impact on the plant than on native plants in the introduced range (Keane and Crawley 2002). The hypothesis is supported by numerous studies comparing the invertebrate predators and diseases of plants in their native and exotic ranges (e.g. Memmott et al. 2000). Such studies have often been undertaken preparatory to classical biological control programs. Enemy release theory has been the “conceptual underpinning” of classical biological control since its inception (Callaway and Maron 2006 p. 371).The numerous examples of pest suppression resulting from practical biological control (Julien and Griffiths 1998) and the very limited non-target impacts of these programs (Waterhouse 1998, Wajnberg et al. 2001) provide strong evidence that enemy release is an important cause of plant invasions: deliberately introduced parasites and predators directly control population growth of some invaders and may have indirect effects on their performance (Prieur-Richard and Lavorel 2000). However, to prevent damage to non-target species, classical biological control is constrained to concentrate on specialist enemies with narrow host ranges. The full trophic complexity of the system in the plant’s native range is extremely difficult to assess and highly variable. Furthermore, succesful biological control of a weed does not necessarily demonstrate that the weed became a problem because of natural enemy release, since the biological control agent itself has been released from its natural enemies. A meta-analysis of 13 studies that quantified the impact of native natural enemies on invasive exotic plants (Keane and Crawley 2002) partially supported the enemy release hypothesis, finding that in every case where native specialist insects were differentiated, they attacked the exotic, however their impact was usually negligible. Native generalist enemies were found to have greater impact on the exotic in only two cases. More recent and comprehensive meta-analyses contradict the suppositions of the enemy release hypothesis (Cox 2004): native generalist predators or “evolutionarily novel enemies” (Parker et al. 2006a) preferentially attack exotic prey, which are poorly adapted to resist them or “defensively naive” (Parker and Hay 2005 p. 965), having had limited coevolutionary history of association with the predators. The“evolutionary naïveté” of the invasive species in the invaded system places it at greater risk of attack by newly encountered generalist herbivores (Parker et al. 2006b). Furthermore, generalist herbivores commonly have greater impact on plant community structure in terrestrial ecosystems than specialists (Parker and Hay 2005 citing Crawley 1989). Parker and Hay (2005) found that native generalist herbivores offered food choices of congeneric or confamilial exotic and native species, significantly preferred, with some exceptions, the exotic plants. Following on from this work, Parker et al. (2006a) reviewed a large number of manipulative field studies involving over 100 exotic plant species and found that native generalist herbivores suppress exotic plants more than native plants, and that exotic herbivores facilitate the abundance and species diversity of exotic plants by preferentially consuming native plants. Invertebrate herbivores were found to have only one third to one fifth the impact of vertebrate herbivores on survival of exotic plants (Parker et al. 2006a). However in the studies examined, the native range of a high proportion of the exotic plants was the same region as that of the exotic herbivore (Parker et al. 2006a), suggesting that exotic plants without a common evolutionary history with the exotic predator, and therefore lacking defenses against them, may be as susceptible to predation as native plants. The effect of native generalist predators on exotic plants is reduced if the plant is closely related (in the same genus) to plants in the introduced range, and six times as strong on genera new to the invaded region (Ricciardi and Ward 2006, Parker et al. 2006b). Invertebrate herbivores are usually specialised to feed on particular plant parts and to particular plant species, groups of related species, or wide ranges of species, whereas vertebrate herbivores are generally adapted to consume plants of a particular life form or plant product (Cox 2004). Closely 10
elated plants have similar defences against herbivores (see references in Ricciardi and Ward 2006) and are likely to share traits that confer resistance to attack, or have similar physiological adaptations that lessen stress and better enable the operation of their defences (Parker et al. 2006b). Exotic predators which share little evolutionary history with either the native or exotic plants show no feeding preference for native species (Parker and Hay 2005). Most studies framed within biotic resistance and/or enemy release hypotheses have largely ignored the role of plant interactions with soil microbes and the acceleration of knowledge of soil microecology. There is good evidence that invasive plants in North America have escaped from the host-specific soil microbes of their homelands and also formed new relationships with nonspecific microbial mutualists in the invaded territory (Callaway and Maron 2006). Mack’s (1989) generalisations about the role of exotic livestock in destruction of native caespitose grasslands in western USA, the South American pampas and Australia, their facilitation of invasion by exotic grasses with which they coevolved and the history of native grassland degradation in Australia (Moore 1973 1993, Groves and Whalley 2002) mesh neatly with the biotic resistance hypothesis. In a sense “exotic plants may thrive not by escaping their native enemies, but by following them” (Parker et al. 1996a p. 1460). N. neesiana may possess pre-adaptations that minimise predation by Australian native herbivores (suggested perhaps by the general presence of native Stipeae in invaded areas in Australia), or the native ecosystems invaded now lack their natural herbivore assemblage (e.g. kangaroos generally absent, extinct macropods and marsupial megafauna). The exotic herbivore assemblage that has invaded native grassland (including an array of invertebrates as well as mammals) may differentially attack the native plants (Parker et al. 2006a), or the ecosystem has been otherwise anthropogenically disturbed, or N. neesiana has other attributes (fecundity, high growth rate etc.) that enable it to overcome the effects of native generalist herbivores (Parker and Hay 2005). The biotic resistance hypothesis,as it relates to plants, is not challenged by evidence that landscape scale areas with high plant species diversity also tend to have higher numbers of exotic plant species. Lonsdale (1999) compared exotic and native plant species richness at 184 landscape-scale sites of wide variation in size and found that the number of exotic plant species, but not their proportion of the flora, increased with native plant species richness. Similar analyses at large landscape scales show similar trends, however the areas invaded are not plant communities - the ecological units that are expected to show biotic resistance - and such trends are at best weak in small areas (Cox 2004). The biotic resistance hypothesis has been further elaborated under the moniker of functional group theory: the idea that the diversity of functional groups rather than species enables resistance (Prieur-Richard and Lavorel 2000). Absence of a particular functional group (e.g. grass seed predators) eases constraints on an invasive plant. The presence of a larger number of functional groups of plants suggests that a larger proportion of available resources are already efficiently captured, so there should be greater resistance to invasion. If there is reduced predator pressure in the new environment, a plant has a lesser requirement for defence and an evolutionary trade-off may occur in which the ‘freed up’ resources are allocated to other purposes, inclduing reproduction. Trade-offs resulting in growth increases and higher investment in reproduction are believed to be common in invasive plants (Cox 2004). The rate at which invasive plants acquire new natural enemies is highly variable, but is generally rapid at first, the diversity of generalist herbivores reaching a maximum in as little as 100 years, then slows, with host shifting by and evolution of specialist herbivores gradually occurring over longer periods, up to 10,000 years (Cox 2004). Major factors influencing these rates are the diversity of the native herbivore and pathogen pools and the extent of their adaptation to phylogenetically related native plants, the phenological availabilityof the invasive plant to the potential native utilisers, and the innate defences of the plant (Cox 2004). The abundance or total area occupied by the invasive plant also appears to be important, e.g. as found in a global study of the arthropod pests of Saccharum officinale, which found that the number of pest species had a linear relationship to the area of sugar cane under cultivation (Cox 2004 citing Strong et al. 1977). It can therefore be hypothesised that N. neesiana is preferentially consumed by native generalist species compared with dominant native grasses, and that exotic generalist plant predators will preferentially consume the dominant native grasses. If this is the case, grasslands with diverse and abundant populations of exotic plant predators should be more susceptible to invasion and more highly invaded by N. neesiana. Grasslands that have inherent biotic resistance should be occupied by native generalist mammalian herbivores including kangaroos, and have a greater diversity of native generalist phytophagous invertebrates. Grasslands without biotic resistance should lack large native mammal herbivores, have a depauperate guild of native generalist grass-feeding invertebrates, and an increased complement of exotic grass-feeding mammals Manipulative field experiments involving predator removal or paired feeding assays (e.g. Parker and Hay 2005) are needed to demonstrate such effects. Resource-enrichment and fluctuating resources A successful invasive plant may simply be a superior competitor for basic resources such as light, water and nutrients. Many biological attributes that engender such superior ability have been identified, for example plants with C 3 and C 4 photosynthetic pathways are superior convertors of sunlight to sugars in different environments, and any one plant may have higher fecundity or a faster growth rate than another. But because resources are ‘locked up’ variably in space and time by the plants in the preexisting community, disturbance that kills or inhibits them and frees up resources is generally required for a successful invasion, or their must be extrinsic addition of resources at a rate faster than the native plants can use (Herbold and Moyle 1986, Hobbs 1991, Burke and Grime 1996, Cox 2004). The tenet that disturbance is a prerequisite for invasion is implicity based on the notion that in undisturbed, successionally mature vegetation, surplus resources are absent (Carr 1993) or minimised or unobtainable by the existing flora. The fluctuating resources theory posits that a “plant community becomes more susceptible to invasion whenever there is an increase in the amount of unused resources” (Davis et al. 2000). The community becomes more susceptible to invasion by a particular exotic plant if the particular resource was previously limiting the growth or survival of that plant (Hobbs 1991). Continuity of the invasion requires that gains the invader makes are not lost when resource supply contracts (Melbourne et al. 2007). 11
Page 1 and 2: Literature review: Impact of Chilea
Page 3 and 4: Fire 49 Other disturbances 50 Shade
Page 5 and 6: Conventions and standards Botanical
Page 7 and 8: neesiana appears to be a habitat ge
Page 9: population densities of existing sp
Page 13 and 14: For invasion to occur there must be
Page 15 and 16: As yet there appears to be no evide
Page 17 and 18: experimental manipulation of specie
Page 19 and 20: species tend to be those which tran
Page 21 and 22: Taxonomy and nomenclature Stipeae N
Page 23 and 24: Vernacular names ‘Needlegrass’
Page 25 and 26: to Bouchenak-Khelladi et al. 2009).
Page 27 and 28: 1 m (Walsh 1994), ca. 90 cm (Verloo
Page 29 and 30: Figure 2. Anatomy of the seed of N.
Page 31 and 32: are the seeds larger/smaller, longe
Page 33 and 34: also based on a misunderstanding of
Page 35 and 36: Table 2. Modified Feekes Scale for
Page 37 and 38: Argentina, in the provinces of Chac
Page 39 and 40: Figure 3. Recorded distribution of
Page 41 and 42: 1994). Only 3 of 186 exotic grasses
Page 43 and 44: According to Morfe et al. (2003) th
Page 45 and 46: populations have been found in the
Page 47 and 48: (Honaine et al. 2006). The flechill
Page 49 and 50: In Australia the altitudinal range
Page 51 and 52: Proximity to urban development appe
Page 53 and 54: In the southern Brazilian campos of
Page 55 and 56: arundinacea (Gardener et al. 2005).
Page 57 and 58: al. 2008). Cues for masting may be
Page 59 and 60: Approximately 200 alien grass speci
Page 61 and 62:
Dispersal of seed in contaminated s
Page 63 and 64:
In New Zealand, Hurrell et al. (199
Page 65 and 66:
No emergence was observed in undist
Page 67 and 68:
and high impact (“ability to caus
Page 69 and 70:
also noted that despite a wide rang
Page 71 and 72:
a small reduction in seedhead produ
Page 73 and 74:
Slashing and mowing Slashing can re
Page 75 and 76:
Themeda re-establishment McDougall
Page 77 and 78:
species (Lawton and Schroder 1977 p
Page 79 and 80:
y increased importance of ant grani
Page 81 and 82:
BIODIVERSITY “Biodiversity ... on
Page 83 and 84:
According to Woods (1997 p. 61) “
Page 85 and 86:
2004, Richardson and van Wilgen 200
Page 87 and 88:
negative depending on the particula
Page 89 and 90:
Competition with native plants Comp
Page 91 and 92:
asexual seed production, so local f
Page 93 and 94:
GRASSLANDS Grasses: “... the most
Page 95 and 96:
susceptible to N. neesiana invasion
Page 97 and 98:
Floristic composition, vegetation s
Page 99 and 100:
proportion of the flora then presen
Page 101 and 102:
tussock space (Stuwe and Parsons 19
Page 103 and 104:
Like vascular plant diversity, comm
Page 105 and 106:
Opinions differ on the nature and i
Page 107 and 108:
Species Common Name Family Aust ACT
Page 109 and 110:
in shifting the distribution, exten
Page 111 and 112:
of these systems is largely explain
Page 113 and 114:
pasture. The least understood trans
Page 115 and 116:
tend to benefit more from relaxed c
Page 117 and 118:
Bovids crop their food between the
Page 119 and 120:
are therefore less likely to distur
Page 121 and 122:
esult in a “short-term flush” o
Page 123 and 124:
Fire effects on weeds Moore (1993 p
Page 125 and 126:
Table 8. Typical nutrient levels in
Page 127 and 128:
grasses produced sigificantly more
Page 129 and 130:
Fossorial vertebrates are or were o
Page 131 and 132:
(Rosengren 1999). Approximately one
Page 133 and 134:
Table 12. Areal extent and conserva
Page 135 and 136:
Foreman (1997) investigated the eff
Page 137 and 138:
Willis (1964) considered that the f
Page 139 and 140:
Austrostipa-Enneapogon) from around
Page 141 and 142:
Woodlands and New England Grassy Wo
Page 143 and 144:
Thylogale billardierii), Peramelida
Page 145 and 146:
Its original habitat on the mainlan
Page 147 and 148:
Table 17. Endangered reptile specie
Page 149 and 150:
equirement, but unlike plants and v
Page 151 and 152:
e assigned the same biodiversity sc
Page 153 and 154:
Nematodes are mostly minute animals
Page 155 and 156:
found in all mainland states, O. co
Page 157 and 158:
Keyacris scurra, Melbourne (1993) o
Page 159 and 160:
was once widespread in south- easte
Page 161 and 162:
eing sluggish and wingless, and exi
Page 163 and 164:
estoration and, if Australia follow
Page 165 and 166:
close to the plant are able to bury
Page 167 and 168:
Species *Chirothrips mexicanus Craw
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Table A2.1 (continued) Species Life
Page 171 and 172:
Table A2.1 (continued) Species *Het
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Nematodes of grasses and grasslands
Page 179 and 180:
REFERENCES Aceñolaza, F.G. (2004)
Page 181 and 182:
Benson, D. and McDougall, L. (2005)
Page 183 and 184:
Chan, C.W. (1980) Natural grassland
Page 185 and 186:
DNRE (Department of Natural Resourc
Page 187 and 188:
Fuhrer, B. (1993) A Field Companion
Page 189 and 190:
Groves, R.H. and Whalley, R.D.B. (2
Page 191 and 192:
Iaconis, L. (2004) Chilean needle g
Page 193 and 194:
Levine, J.M., Adler, P.B. and Yelen
Page 195 and 196:
McDougall, K.L. (1987) Sites of Bot
Page 197 and 198:
Morfe, T.A., McLaren, D.A. and Weis
Page 199 and 200:
Perelman, S.B., León, R.J.C. and O
Page 201 and 202:
Saunders, D.A. (1999) Biodiversity
Page 203 and 204:
Thellung, A. (1912) La flore advent
Page 205 and 206:
Weiss, J. and McLaren, D. (2002) Vi
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