"Kay" wrote in message
...
snip

Should we regard the earth as our habitat, and whatever we do to make it
better for us is therefore good, even if it is bad for other species?

Sounds like a good idea to me*. I'm presuming for example, that if you had
lice you wouldn't leave them on your body, even though that is 'good for
you' and 'bad for lice'? Or that if slugs were eating your food, you
wouldn't either kill the ones eating your food or restrict their access to
your food (both the same thing in the long run). [the third possibility, to
relocate them, would damage some other species food supply of course, not to
mention the plants themselves]


Or is the earth something that should be preserved even if it means
curing our instincts to dominate?

The earth cant be "preserved". But even if it could, then that would be
gross interference in itself, if for example you 'preserved' every species
that was going extinct, even if that extinction was nothing to do with us.
That would definitely be a bad thing, from the POV of letting nature operate
unhindered by us.


And neither of those questions is relevant to global warming etc because
if we mess up the earth it will mess us up too. So whether our motives
are to look after it for its own sake or to further our success as a
species, it's still a sensible thing to do.


*Well that should obviously be taken into account when deciding what to do
with our habitat as per the first point. But eradicating, for example the
malaria parasite ,I'm betting you'd regard as a good thing even though its a
'very bad thing' for the malaria parasite. So really, all you would disagree
with, is in what degree and way you'd interfere, rather than setting
yourself up as some special case who doesn't change the planet and everyone
else who does is evil.

--
Tumbleweed

email replies not necessary but to contact use;
tumbleweednews at hotmail dot com

In article , Tumbleweed thisaccountneverr
writes

"Kay" wrote in message
...
snip

Should we regard the earth as our habitat, and whatever we do to make it
better for us is therefore good, even if it is bad for other species?

Sounds like a good idea to me*. I'm presuming for example, that if you had
lice you wouldn't leave them on your body, even though that is 'good for
you' and 'bad for lice'?

But would I, if I had the opportunity, eradicate them entirely from the
earth?
Bad for an individual louse is not the same as bad for lice as a species


Or is the earth something that should be preserved even if it means
curing our instincts to dominate?

The earth cant be "preserved".

OK - bad choice of word. What I'm trying to get at is the concept of
'treading lightly' - not having a disproportionate effect. Atm we are so
numerous and so technologically capable that simply going about our
business can have a hugely harmful effect on the world - we have to
consciously think about the effect we are having and take measures to
reduce it if we are to balance our effect to be at a similar level to
that of other species.

But even if it could, then that would be
gross interference in itself, if for example you 'preserved' every species
that was going extinct, even if that extinction was nothing to do with us.
That would definitely be a bad thing, from the POV of letting nature operate
unhindered by us.

But I wasn't advocating that, as I hope is now clear.


And neither of those questions is relevant to global warming etc because
if we mess up the earth it will mess us up too. So whether our motives
are to look after it for its own sake or to further our success as a
species, it's still a sensible thing to do.


*Well that should obviously be taken into account when deciding what to do
with our habitat as per the first point. But eradicating, for example the
malaria parasite ,I'm betting you'd regard as a good thing even though its a
'very bad thing' for the malaria parasite.

That's not a question I could answer without knowing where the malaria
parasite fits in with the rest of the world. Do we know enough to know
we could eradicate it without unexpected effects elsewhere?

Malaria is a bad thing for the individual human. There may be ways to
control its ill effects without targeting the parasite itself (OK we
haven't found any yet). But on the global scale, part of the problem is
that we have struggled to the top of the heap so successfully, so that
as a species we have a huge effect on the world. We are now actively
trying to curb global warming - if we don't bother, what might the
scenario be? Does earth heat up to the extent of being home only to a
few specialised bacteria, or do increasing floods etc take their toll on
the human species and put a natural limit to the process?

So really, all you would disagree
with, is in what degree and way you'd interfere, rather than setting
yourself up as some special case who doesn't change the planet and everyone
else who does is evil.

Eh? Are you suggesting I am
setting
yourself up as some special case who doesn't change the planet and everyone
else who does is evil.

That doesn't follow from what I said, so I guess I must have got up your
nose on some previous occasion. Ah well.
--
Kay
"Do not insult the crocodile until you have crossed the river"

In article , Franz Heymann notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong, and 5 and 6 are not primarily 'for the sake of humans or
domesticated animals' - indeed, it was the *introduction* of hedgehogs
that was 'for the sake of humans'.

And no 2 is an interesting one ... where do we draw the line .. how do
we regard viruses, compared with plants, animals, fungi, bacteria ...


--
Kay
"Do not insult the crocodile until you have crossed the river"

"Kay" wrote in message
...
In article , Franz Heymann notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong,

What do you mean by 'places where they don't belong'? Pretty obviously, they
are well suited to those places, or they wouldn't be thriving to the extent
they are thought to be interfering with some humans' preferences for those
places. Mind you, much conservation seems to be about trying to control
organisms which are successful to preserve and encourage less successful
organisms which we prefer, a concept with which all gardeners will be
familiar.

and 5 and 6 are not primarily 'for the sake of humans or
domesticated animals' - indeed, it was the *introduction* of hedgehogs
that was 'for the sake of humans'.

The extermination of the hedgehogs is for the sake of humans, too. It is for
the sake of those humans who consider the continued presence on the islands
of large breeding populations of certain species of birds to be important,
and who believe that management of the hedgehog population is therefore a
necessary expedient. If the presence of the hedgehogs merely threatened the
survival on the islands of something to which humans assigned little
importance (like the slugs they were reputedly imported to control), I
doubt whether the RSPB or the local tourist industry would have lobbied SNH
for their removal.


And no 2 is an interesting one ... where do we draw the line .. how do
we regard viruses, compared with plants, animals, fungi, bacteria ...



I suggest that similar principles apply - if a virus or any other organism
is perceived as a threat/nuisance, countermeasures are likely to be taken up
to the point where the cost/effort/hassle involved starts to outweigh the
anticipated benefits.

"Kay" wrote in message
...
In article , Franz Heymann
notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to
such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they
don't
belong, and 5 and 6 are not primarily 'for the sake of humans or
domesticated animals' - indeed, it was the *introduction* of
hedgehogs
that was 'for the sake of humans'.

And no 2 is an interesting one ... where do we draw the line .. how
do
we regard viruses, compared with plants, animals, fungi, bacteria
....

That's a good question. I tnd to tink of anything which replicates
itself as being in some sense alive, but that may well be wrong.

Franz

In article ,
"Franz Heymann" writes:
|
| That's a good question. I tnd to tink of anything which replicates
| itself as being in some sense alive, but that may well be wrong.

Prions.


Regards,
Nick Maclaren.

In article , BAC
writes

"Kay" wrote in message
...
In article , Franz Heymann notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong,

What do you mean by 'places where they don't belong'?

They didn't get there without human intervention.

Pretty obviously, they
are well suited to those places,

I can think of many places where I would thrive, but where I don't
belong ;-)

and 5 and 6 are not primarily 'for the sake of humans or
domesticated animals' - indeed, it was the *introduction* of hedgehogs
that was 'for the sake of humans'.

The extermination of the hedgehogs is for the sake of humans, too. It is for
the sake of those humans who consider the continued presence on the islands
of large breeding populations of certain species of birds to be important,
and who believe that management of the hedgehog population is therefore a
necessary expedient. If the presence of the hedgehogs merely threatened the
survival on the islands of something to which humans assigned little
importance (like the slugs they were reputedly imported to control), I
doubt whether the RSPB or the local tourist industry would have lobbied SNH
for their removal.

OK, a fair point.


And no 2 is an interesting one ... where do we draw the line .. how do
we regard viruses, compared with plants, animals, fungi, bacteria ...



I suggest that similar principles apply - if a virus or any other organism
is perceived as a threat/nuisance, countermeasures are likely to be taken up
to the point where the cost/effort/hassle involved starts to outweigh the
anticipated benefits.

That leaves questions about what are the benefits. Will removal of one
species (whatever it is) have a knock on effect on others? Is it good to
maintain as large a number of species as possible for its own sake? ..
or for potential future uses we don't yet know about? And how much
importance should we place on the furry cuddly factor?



--
Kay
"Do not insult the crocodile until you have crossed the river"

In article , Franz Heymann
writes

"Kay" wrote in message
...

And no 2 is an interesting one ... where do we draw the line .. how
do
we regard viruses, compared with plants, animals, fungi, bacteria
...

That's a good question. I tnd to tink of anything which replicates
itself as being in some sense alive, but that may well be wrong.

Computer worm?


--
Kay
"Do not insult the crocodile until you have crossed the river"

In article ,
Kay writes:
|
| What do you mean by 'places where they don't belong'?
|
| They didn't get there without human intervention.

Grrk. That accounts for most of our ecologies, including such ones
as chalk downland. The UK has very few ecologies that are even
semi-natural.

| Pretty obviously, they
| are well suited to those places,
|
| I can think of many places where I would thrive, but where I don't
| belong ;-)

I can think of a few, too :-)


Regards,
Nick Maclaren.

"Kay" wrote in message
...
In article , BAC
writes

"Kay" wrote in message
...
In article , Franz Heymann
notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong,

What do you mean by 'places where they don't belong'?

They didn't get there without human intervention.

Whether it "didnt belong there' is a human value judgement. Had, in
pre-human times, a chance event carried prickly pear seed to Oz, and it had
become established, presumably you'd now be saying it did 'belong there'?


--
Tumbleweed

email replies not necessary but to contact use;
tumbleweednews at hotmail dot com

"Kay" wrote in message
...
In article , Tumbleweed thisaccountneverr
writes

"Kay" wrote in message
...
snip

Should we regard the earth as our habitat, and whatever we do to make
it
better for us is therefore good, even if it is bad for other species?

Sounds like a good idea to me*. I'm presuming for example, that if you
had
lice you wouldn't leave them on your body, even though that is 'good for
you' and 'bad for lice'?

But would I, if I had the opportunity, eradicate them entirely from the
earth?
Bad for an individual louse is not the same as bad for lice as a species

Its the start. Logically, if you would eradicate them from yourself, that is
equivalent to saying you believe they should be eradicated totally. How
would you propose to not eradicate human lice? Would you mandate that some
people should keep them for the benefit of the lice species?



Or is the earth something that should be preserved even if it means
curing our instincts to dominate?

The earth cant be "preserved".

OK - bad choice of word. What I'm trying to get at is the concept of
'treading lightly' - not having a disproportionate effect. Atm we are so
numerous and so technologically capable that simply going about our
business can have a hugely harmful effect on the world - we have to

I think you''ll have to define 'harmful' and I suspect it will boil down to
what is good for us, rather than what is good for 'the world' (whatever
'good' and 'the world' means*). For example, you might say 'if we change
the ecosystem too much in direction X, that will cause us problems, so we
shouldnt do it'. Or 'if we eradicate species Y, future generations wont gain
enjoyment from them, or, that will cause a knock-on effect on the
ecosystems which will damage us. Unless you'd say something else?


consciously think about the effect we are having and take measures to
reduce it if we are to balance our effect to be at a similar level to
that of other species.

Why should we do that? And how would you measure it? How would you define
the level? Whats the number of seagull equivalents to people? Or hedgehogs?
Or nematodes?


But even if it could, then that would be
gross interference in itself, if for example you 'preserved' every
species
that was going extinct, even if that extinction was nothing to do with
us.
That would definitely be a bad thing, from the POV of letting nature
operate
unhindered by us.

But I wasn't advocating that, as I hope is now clear.

Nope, I'm not quite sure what you are advocating.



And neither of those questions is relevant to global warming etc
because
if we mess up the earth it will mess us up too. So whether our motives
are to look after it for its own sake or to further our success as a
species, it's still a sensible thing to do.


*Well that should obviously be taken into account when deciding what to
do
with our habitat as per the first point. But eradicating, for example the
malaria parasite ,I'm betting you'd regard as a good thing even though
its a
'very bad thing' for the malaria parasite.

That's not a question I could answer without knowing where the malaria
parasite fits in with the rest of the world. Do we know enough to know
we could eradicate it without unexpected effects elsewhere?

Ah, the good old 'precautionary principle'. If we operated by that,we would
never do anything. Besides which, *not* doing something is also making a
choice that has repercussions. Perhaps if we didnt eradicate the malaria
parasite, it would in 500 years evolve into a new strain that was far more
virulent and killed billions of people and perhaps also infected pandas and
made them extinct? There are too many 'what ifs' to use the PP as an excuse.

And malaria is the same issue as lice. Thought experiment.....**you** have
the last colonies of several hundred each of human lice, fleas, ticks etc.
Do you kill them? **you** are the last person with malaria. Should you take
the drug that will cure you?


Malaria is a bad thing for the individual human. There may be ways to
control its ill effects without targeting the parasite itself (OK we
haven't found any yet). But on the global scale, part of the problem is
that we have struggled to the top of the heap so successfully, so that
as a species we have a huge effect on the world.

I see nothing wrong with having a huge effect on the world. It also depends
how you measure it, as to what 'huge' is.


We are now actively
trying to curb global warming - if we don't bother, what might the
scenario be?

FWIW, even if we did bother (and I see few signs we are) it would have
little effect on GW, that train left the station some considerable time ago.
By little effect, I mean that, for example, if Kyoto was established *now*,
it would make the difference that instead of the temp being 'X' in one
hundred years time, it would be 'X' in 104 years time. Perhaps better to
spend the money on whatever the effects of GW would be, or on clean water or
something else?

Does earth heat up to the extent of being home only to a
few specialised bacteria, or do increasing floods etc take their toll on
the human species and put a natural limit to the process?

What increasing floods?

--
Tumbleweed

*wooly phrases that everyone uses and means something different by.

email replies not necessary but to contact use;
tumbleweednews at hotmail dot com

In article , Tumbleweed thisaccountneverr
writes

"Kay" wrote in message
...
In article , BAC
writes

"Kay" wrote in message
...
In article , Franz Heymann
notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong,

What do you mean by 'places where they don't belong'?

They didn't get there without human intervention.

Whether it "didnt belong there' is a human value judgement. Had, in
pre-human times, a chance event carried prickly pear seed to Oz, and it had
become established, presumably you'd now be saying it did 'belong there'?


It wouldn't have arrived there as a result of human activity. OK, you
can say that it's irrelevant which species brought it there - whether it
came on a duck's foot or in a human's hand baggage, for example, but
what this discussion is leading me to believe is that there is a
quantitative difference between us and other species - we do things more
purposefully and on a larger scale, and therefore have a larger effect.

Had Opuntia arrived in Oz as chance seeds in pre-human times, they would
have established more slowly, other things would have evolved around
them. They would not have become the problem that they did.

--
Kay
"Do not insult the crocodile until you have crossed the river"

"Kay" wrote in message
...
In article , BAC
writes

"Kay" wrote in message
...
In article , Franz Heymann
notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they don't
belong,

What do you mean by 'places where they don't belong'?

They didn't get there without human intervention.

Right, so we're back to the 'non-native' judgement again.


Pretty obviously, they
are well suited to those places,

I can think of many places where I would thrive, but where I don't
belong ;-)

LOL, if you would thrive in them, you would seem suited to them.


and 5 and 6 are not primarily 'for the sake of humans or
domesticated animals' - indeed, it was the *introduction* of hedgehogs
that was 'for the sake of humans'.

The extermination of the hedgehogs is for the sake of humans, too. It is
for
the sake of those humans who consider the continued presence on the
islands
of large breeding populations of certain species of birds to be
important,
and who believe that management of the hedgehog population is therefore a
necessary expedient. If the presence of the hedgehogs merely threatened
the
survival on the islands of something to which humans assigned little
importance (like the slugs they were reputedly imported to control), I
doubt whether the RSPB or the local tourist industry would have lobbied
SNH
for their removal.

OK, a fair point.


And no 2 is an interesting one ... where do we draw the line .. how do
we regard viruses, compared with plants, animals, fungi, bacteria ...



I suggest that similar principles apply - if a virus or any other
organism
is perceived as a threat/nuisance, countermeasures are likely to be taken
up
to the point where the cost/effort/hassle involved starts to outweigh the
anticipated benefits.

That leaves questions about what are the benefits.

Will removal of one
species (whatever it is) have a knock on effect on others?

Removal of a species may or may not have a significant knock on effect,
adverse or beneficial, we do not know. Extinction is a fact of nature,
however.

Is it good to
maintain as large a number of species as possible for its own sake?

Depends what you mean by 'good', I suppose. Expressing belief in the supreme
merit of the maximisation of biodiversity seems to be a tenet of faith
amongst people engaged in conservation these days.

or for potential future uses we don't yet know about?

One way I have seen suggested for putting a value on a species is to
estimate the total monetary worth of anything and everything which might be
done with it in the future. As we have no way of knowing what might be done
in the future, virtually every species can be argued to have an infinite
value on that approach. Like every premium bond might hit the jackpot, one
day, although that doesn't stop us from cashing them in for short term gain
when we feel like it :-)


And how much
importance should we place on the furry cuddly factor?

That and aesthetics? As much as we each consider appropriate, surely? After
all, it seems to be in our species' nature to modify our surroundings to
suit our own preferences. As gardeners, we do it all the time, don't we? Are
you suggesting that instead of growing things we like, we should cultivate
things we are told are 'worthy'? That'd be the day I gave up gardening.

In article , Tumbleweed thisaccountneverr
writes


"Kay" wrote in message
...
In article , Tumbleweed thisaccountneverr
writes

"Kay" wrote in message
...
snip

Should we regard the earth as our habitat, and whatever we do to make
it
better for us is therefore good, even if it is bad for other species?

Sounds like a good idea to me*. I'm presuming for example, that if you
had
lice you wouldn't leave them on your body, even though that is 'good for
you' and 'bad for lice'?

But would I, if I had the opportunity, eradicate them entirely from the
earth?
Bad for an individual louse is not the same as bad for lice as a species

Its the start. Logically, if you would eradicate them from yourself, that is
equivalent to saying you believe they should be eradicated totally.

No - but I do realise it's a bit selfish to ask other people to put up
with them if I won't ;-)

How
would you propose to not eradicate human lice?

We haven't done it yet, despite throwing all sorts of chemicals at them!
And no, I can't work up a lot of enthusiasm for them.

OK - bad choice of word. What I'm trying to get at is the concept of
'treading lightly' - not having a disproportionate effect. Atm we are so
numerous and so technologically capable that simply going about our
business can have a hugely harmful effect on the world - we have to

I think you''ll have to define 'harmful'

Not a definition, but I think I mean 'causing a large change'. And I'm
not about to try to pind down 'large'.

and I suspect it will boil down to
what is good for us, rather than what is good for 'the world' (whatever
'good' and 'the world' means*).

Undoubtedly that is the definition some people would use.

For example, you might say 'if we change
the ecosystem too much in direction X, that will cause us problems, so we
shouldnt do it'. Or 'if we eradicate species Y, future generations wont gain
enjoyment from them, or, that will cause a knock-on effect on the
ecosystems which will damage us. Unless you'd say something else?

Yes, in my contemplative moments, I would look on it as not causing too
much change to the world, and that is incompatible with the success of
the human species. I don't feel particularly wedded to the need for the
human race to continue successfully. Which is not to say that I can view
human suffering with equanimity.


consciously think about the effect we are having and take measures to
reduce it if we are to balance our effect to be at a similar level to
that of other species.

Why should we do that?

For the good of the world? Because we consider ourselves to better than
animals? But why is 'the world' more worthy of care than the human
species? I don't know. Perhaps the 'devil takes the hindmost' approach
is the only sensible one.


And how would you measure it? How would you define
the level? Whats the number of seagull equivalents to people? Or hedgehogs?
Or nematodes?

You'd look at the changes in species abundances and at the changes in
physical conditions.


Nope, I'm not quite sure what you are advocating.

Ah well, that's life.


And malaria is the same issue as lice. Thought experiment.....**you** have
the last colonies of several hundred each of human lice, fleas, ticks etc.
Do you kill them? **you** are the last person with malaria. Should you take
the drug that will cure you?

Quite possibly not. But what I should do and what I do do are frequently
two entirely different things.


Does earth heat up to the extent of being home only to a
few specialised bacteria, or do increasing floods etc take their toll on
the human species and put a natural limit to the process?

What increasing floods?

The various things I've read which suggest rise in sea levels, and also
increasing extremes of weather - though I am quite likely out of date on
this. But I did say 'etc' - or are you saying GW isn't going to be a
problem to humans in any way?


--
Kay
"Do not insult the crocodile until you have crossed the river"

"Kay" wrote in message
...
In article , Tumbleweed thisaccountneverr
writes

"Kay" wrote in message
...
In article , BAC
writes

"Kay" wrote in message
...
In article , Franz Heymann
notfranz.
writes


It would be unwise for a pragmatist like me to say yes or no to
such a
possible false generalisation.
There are circumstances where I would be prepared to participate in
the eradication of some species in certain places for the sake of
humans, or domesticated animals, for example

Prickly pears for the sake of grazing field
The common cold virus
Malaria-carrying mosquitoes
Bracken in the Lake District
Hedgehogs in N Uist and Benbecula
Cats on Marion Island

Well, out of that lot, nos 1, 5 and 6 could be regarded as putting
things right after introduction of species to places where they
don't
belong,

What do you mean by 'places where they don't belong'?

They didn't get there without human intervention.

Whether it "didnt belong there' is a human value judgement. Had, in
pre-human times, a chance event carried prickly pear seed to Oz, and it
had
become established, presumably you'd now be saying it did 'belong there'?


It wouldn't have arrived there as a result of human activity. OK, you
can say that it's irrelevant which species brought it there - whether it
came on a duck's foot or in a human's hand baggage, for example, but
what this discussion is leading me to believe is that there is a
quantitative difference between us and other species - we do things more
purposefully and on a larger scale, and therefore have a larger effect.

Had Opuntia arrived in Oz as chance seeds in pre-human times, they would
have established more slowly, other things would have evolved around
them. They would not have become the problem that they did.


Had Opuntia arrived in Oz as chance seeds in prehuman times, and
proliferated exponentially, you are right to say they would not have become
a problem, because there would not have been anyone on hand to perceive
their presence and their effect on that ecosystem as problems.